gamma correction for lcd monitors made in china

Problems like extremely poor display of shadow areas, blown-out highlights, or images prepared on Macs appearing too dark on Windows computers are often due to gamma characteristics. In this session, we"ll discuss gamma, which has a significant impact on color reproduction on LCD monitors. Understanding gamma is useful in both color management and product selection. Users who value picture quality are advised to check this information.

* Below is the translation from the Japanese of the ITmedia article "Is the Beauty of a Curve Decisive for Color Reproduction? Learning About LCD Monitor Gamma" published July 13, 2009. Copyright 2011 ITmedia Inc. All Rights Reserved.

The term gamma comes from the third letter of the Greek alphabet, written Γ in upper case and γ in lower case. The word gamma occurs often in everyday life, in terms like gamma rays, the star called Gamma Velorum, and gamma-GTP. In computer image processing, the term generally refers to the brightness of intermediate tones (gray).

Let"s discuss gamma in a little more detail. In a PC environment, the hardware used when working with color includes monitors, printers, and scanners. When using these devices connected to a PC, we input and output color information to and from each device. Since each device has its own unique color handling characteristics (or tendencies), color information cannot be output exactly as input. The color handling characteristics that arise in input and output are known as gamma characteristics.

While certain monitors are also compatible with color handling at 10 bits per RGB color (210 = 1024 tones), or 1024 x 3 (approximately 1,064,330,000 colors), operating system and application support for such monitors has lagged. Currently, some 16.77 million colors, with eight bits per RGB color, is the standard color environment for PC monitors.

When a PC and a monitor exchange color information, the ideal is a relationship in which the eight-bit color information per RGB color input from the PC to the monitor can be output accurately—that is, a 1:1 relationship for input:output. However, since gamma characteristics differ between PCs and monitors, color information is not transmitted according to a 1:1 input:output relationship.

How colors ultimately look depends on the relationship resulting from the gamma values (γ) that numerically represent the gamma characteristics of each hardware device. If the color information input is represented as x and output as y, the relationship applying the gamma value can be represented by the equation y = xγ.

Gamma characteristics are represented by the equation y = xγ. At the ideal gamma value of 1.0, y = x; but since each monitor has its own unique gamma characteristics (gamma values), y generally doesn"t equal x. The above graph depicts a curve adjusted to the standard Windows gamma value of 2.2. The standard gamma value for the Mac OS is 1.8.

Ordinarily, the nature of monitor gamma is such that intermediate tones tend to appear dark. Efforts seek to promote accurate exchange of color information by inputting data signals in which the intermediate tones have already been brightened to approach an input:output balance of 1:1. Balancing color information to match device gamma characteristics in this way is called gamma correction.

A simple gamma correction system. If we account for monitor gamma characteristics and input color information with gamma values adjusted accordingly (i.e., color information with intermediate tones brightened), color handling approaches the y = x ideal. Since gamma correction generally occurs automatically, users usually obtain correct color handling on a PC monitor without much effort. However, the precision of gamma correction varies from manufacturer to manufacturer and from product to product (see below for details).

In most cases, if a computer runs the Windows operating system, we can achieve close to ideal colors by using a monitor with a gamma value of 2.2. This is because Windows assumes a monitor with a gamma value of 2.2, the standard gamma value for Windows. Most LCD monitors are designed based on a gamma value of 2.2.

The standard monitor gamma value for the Mac OS is 1.8. The same concept applies as in Windows. We can obtain color reproduction approaching the ideal by connecting a Mac to a monitor configured with a gamma value of 1.8.

An example of the same image displayed at gamma values of 2.2 (photo at left) and 1.8 (photo at right). At a gamma value of 1.8, the overall image appears brighter. The LCD monitor used is EIZO"s 20-inch wide-screen EV2023W FlexScan model (ITmedia site).

To equalize color handling in mixed Windows and Mac environments, it"s a good idea to standardize the gamma values between the two operating systems. Changing the gamma value for the Mac OS is easy; but Windows provides no such standard feature. Since Windows users perform color adjustments through the graphics card driver or separate color-adjustment software, changing the gamma value can be an unexpectedly complex task. If the monitor used in a Windows environment offers a feature for adjusting gamma values, obtaining more accurate results will likely be easier.

If we know that a certain image was created in a Mac OS environment with a gamma value of 1.8, or if an image received from a Mac user appears unnaturally dark, changing the monitor gamma setting to 1.8 should show the image with the colors intended by the creator.

Eizo Nanao"s LCD monitors allow users to configure the gamma value from the OSD menu, making this procedure easy. In addition to the initially configured gamma value of 2.2., one can choose from multiple settings, including the Mac OS standard of 1.8.

To digress slightly, standard gamma values differ between Windows and Mac OS for reasons related to the design concepts and histories of the two operating systems. Windows adopted a gamma value corresponding to television (2.2), while the Mac OS adopted a gamma value corresponding to commercial printers (1.8). The Mac OS has a long history of association with commercial printing and desktop publishing applications, for which 1.8 remains the basic gamma value, even now. On the other hand, a gamma value of 2.2 is standard in the sRGB color space, the standard for the Internet and for digital content generally, and for Adobe RGB, the use of which has expanded for wide-gamut printing,.

Given the proliferating use of color spaces like sRGB and Adobe RGB, plans call for the latest Mac OS scheduled for release by Apple Computer in September 2009, Mac OS X 10.6 Snow Leopard, to switch from a default gamma value of 1.8 to 2.2. A gamma value of 2.2 is expected to become the future mainstream for Macs.

On the preceding page, we mentioned that the standard gamma value in a Windows environment is 2.2 and that many LCD monitors can be adjusted to a gamma value of 2.2. However, due to the individual tendencies of LCD monitors (or the LCD panels installed in them), it"s hard to graph a smooth gamma curve of 2.2.

Traditionally, LCD panels have featured S-shaped gamma curves, with ups and downs here and there and curves that diverge by RGB color. This phenomenon is particularly marked for dark and light tones, often appearing to the eye of the user as tone jumps, color deviations, and color breakdown.

The internal gamma correction feature incorporated into LCD monitors that emphasize picture quality allows such irregularity in the gamma curve to be corrected to approach the ideal of y = x γ. Device specs provide one especially useful figure to help us determine whether a monitor has an internal gamma correction feature: A monitor can be considered compatible with internal gamma correction if the figure for maximum number of colors is approximately 1,064,330,000 or 68 billion or if the specs indicate the look-up table (LUT) is 10- or 12-bit.

An internal gamma correction feature applies multi-gradation to colors and reallocates them. While the input from a PC to an LCD monitor is in the form of color information at eight bits per RGB color, within the LCD monitor, multi-gradation is applied to increase this to 10 bits (approximately 1,064,330,000 colors) or 12 bits (approximately 68 billion colors). The optimal color at eight bits per RGB color (approximately 16.77 million colors) is identified by referring to the LUT and displayed on screen. This corrects irregularity in the gamma curve and deviations in each RGB color, causing the output on screen to approach the ideal of y = x γ.

Let"s look at a little more information on the LUT. The LUT is a table containing the results of certain calculations performed in advance. The results for certain calculations can be obtained simply by referring to the LUT, without actually performing the calculations. This accelerates processing and reduces the load on a system. The LUT in an LCD monitor identifies the optimal eight-bit RGB colors from multi-gradation color data of 10 or more bits.

An overview of an internal gamma correction feature. Eight-bit RGB color information input from the PC is subjected to multi-gradation to 10 or more bits. This is then remapped to the optimal eight-bit RGB tone by referring to the LUT. Following internal gamma correction, the results approach the ideal gamma curve, dramatically improving on screen gradation and color reproduction.

Eizo Nanao"s LCD monitors proactively employ internal gamma correction features. In models designed especially for high picture quality and in some models in the ColorEdge series designed for color management, eight-bit RGB input signals from the PC are subjected to multi-gradation, and calculations are performed at 14 or 16 bits. A key reason for performing calculations at bit counts higher than the LUT bit count is to improve gradation still further, particularly the reproduction of darker tones. Users seeking high-quality color reproduction should probably choose a monitor model like this one.

In conclusion, we"ve prepared image patterns that make it easy to check the gamma values of an LCD monitor, based on this session"s discussion. Looking directly at your LCD monitor, move back slightly from the screen and gaze at the following images with your eyes half-closed. Visually compare the square outlines and the stripes around them, looking for patterns that appear to have the same tone of gray (brightness). The pattern for which the square frame and the striped pattern around it appear closest in brightness represents the rough gamma value to which the monitor is currently configured.

Based on a gamma value of 2.2, if the square frame appears dark, the LCD monitor"s gamma value is low. If the square frame appears bright, the gamma value is high. You can adjust the gamma value by changing the LCD monitor"s brightness settings or by adjusting brightness in the driver menu for the graphics card.

Naturally, it"s even easier to adjust the gamma if you use a model designed for gamma value adjustments, like an EIZO LCD monitor. For even better color reproduction, you can set the gamma value and optimize color reproduction by calibrating your monitor.

Characteristics of the present invention are, the part that differs greatly at the gamma curve of different colours, respectively according to the gamma curve of different colours, the value of the gray scale voltage of decision output gray scale voltage output circuit, and with the corresponding relation of picture element signal.So, when carrying out gamma correction, no matter the color of picture element signal correspondence why, and the value of picture element signal and gray scale voltage all is the linear ratio relation, to improve the image display quality of liquid crystal panel.

Please refer to Fig. 5, it illustrates the circuit diagram of the first kind of gray scale voltage output circuit that proposes according to the preferred embodiments of the present invention.Gray scale voltage output circuit 500 is exported 256 gray scale voltages in order to send out reference pixel voltage according to input.Wherein, each gray scale voltage is corresponding to a picture element signal.Be noted that complete gray scale voltage output circuit need comprise two as the gray scale voltage output circuit 500 that Fig. 5 illustrated, in order to export 256 positive polarity gray scale voltages and 256 negative polarity gray scale voltages respectively.The principle of operation of two gray scale voltage output circuits and method are all closely similar, so after the principle of operation and method of one of them gray scale voltage output circuit 500 of explanation, any those skilled in the art all can push away easily the principle of operation and the method for another gray scale voltage output circuit.

Please refer to Fig. 6 A, it illustrates and is suitable for the gamma curve graph of a relation that gray scale voltage output circuit shown in Figure 5 is carried out gamma correction.In Fig. 6 A, three curves that indicate R, G, B are represented when the pixel demonstration is red, green and blue the gray scale voltage of input pixel and the corresponding relation of pixel intensity respectively.The gamma curve that illustrates by Fig. 6 A as can be known, when pixel voltage hour, for the pixel that shows different colours, the difference of pixel intensity is very little, can ignore.Yet when pixel voltage was big more, the difference of pixel intensity also can increase thereupon.

In the present embodiment, the resistance string of common gray scale voltage output circuit 502 for being in series by 191 resistance.This resistance string has 5 input nodes, in order to input common reference voltage V4, V5, V6, V7 and V8, also has 192 output nodes, respectively in order to export common gray scale voltage VO0～VO191 respectively.According to the law of partial pressure, by the resistance of suitably choosing each resistance, promptly may command is from the value of the gray scale voltage of each output node output.The value of reference voltage V4～V8 is illustrated among Fig. 6 A.In Fig. 6 A, the gamma curve of different colours and the corresponding part of reference voltage V4～V8, difference each other is minimum.Common gray scale voltage output circuit 502 is exported gray scale voltage VO0, VO1 according to reference voltage V4～V8 ... VO191 is corresponding with picture element signal 0～191 (representing with decade) respectively.And for picture element signal 0～191, itself and gray scale voltage VO0, VO1 ... the corresponding relation of VO191, not different along with the Show Color of pixel.

Referring again to Fig. 6 A and Fig. 6 B, in Fig. 6 A, when pixel voltage is big more, the pixel that Show Color is different, the difference of its brightness also can increase thereupon.Fig. 6 B is the enlarged drawing in the zone shown in Fig. 6 A center line.In Fig. 6 B, the gamma curve of different colours difference is to each other showing, and can strengthen along with the increase of gray scale voltage.In order to make the linear ratio relation of picture element signal and pixel intensity, difference to some extent not along with the Show Color of pixel.The present invention is by indivedual gray scale voltage output circuits 504, and according in the gamma curve of red, blue, green three looks, the part that differs greatly (part shown in Fig. 6 B) is exported different gray scale voltages respectively.

In the present embodiment, indivedual gray scale voltage output circuits 504 include red gray scale voltage output circuit 506, green gray scale voltage output circuit 508 and bluish grey rank voltage follower circuit 510 according to the Show Color of pixel on the general color liquid crystal panel.With red gray scale voltage output circuit 506 is example, its resistance string for being in series by 64 resistance.This resistance string has 3 input nodes, in order to input common reference voltage V1R, V2R and V3R, also has 64 output nodes, respectively in order to export red gray scale voltage VO192r～VO255r respectively.Wherein, from the red gray scale voltage VO192r～VO255r of each output node output, its value is according to the gamma curve shown in Fig. 6 B " R " decide.Its mode has two, one, by suitably choosing each resistance (resistance of Rr0～Rr63).Another mode is by the reference voltage that suitably determines the input resistance string (value of V1R～V3R), and each input node position in resistance string.So, according to the law of partial pressure, can determine value from the gray scale voltage of each output node output.Referring again to Fig. 6 B, because reference voltage V1R must be by the input node input topmost of red gray scale voltage output circuit 506, so can only control the value of the gray scale voltage of output by the value of control V1R.But for reference voltage V2R and V3R, can pass through the value of control reference voltage V2R and V3R simultaneously, and on the red gray scale voltage output circuit 506, the position of corresponding input node, decision is from the value of the gray scale voltage of each output node output.By the value of decision, make that the brightness of picture element signal 192～255 and pixel is according to gamma curve from the red gray scale voltage VO192r～VO255r of red gray scale voltage output circuit 506 outputs " R ", be the linear ratio relation.

The circuit of green gray scale voltage output circuit 508 and bluish grey rank voltage follower circuit 510 and operation principles are similar to above-mentioned red gray scale voltage output circuit 506, repeat no more in this.Be noted that green gray scale voltage output circuit 508 and bluish grey rank voltage follower circuit 510 are respectively according to the gamma curve shown in Fig. 6 A～6B " G " reach " B ", decide the value of the gray scale voltage of output.So in green gray scale voltage output circuit 508 and the bluish grey rank voltage follower circuit 510, the resistance of each resistance, the value of each reference voltage, and with the corresponding input node of reference voltage in the position of resistance string, can be not identical with red gray scale voltage output circuit 506.So, make green gray scale voltage VO192g～VO255g from green gray scale voltage output circuit 508 outputs, the brightness of its corresponding picture element signal 192～255 and pixel is according to gamma curve " G " be the linear ratio relation.And from the bluish grey rank voltage VO192b～VO255b of bluish grey rank voltage follower circuit 510 output, the brightness of its corresponding picture element signal 192～255 and pixel is according to gamma curve " B " be the linear ratio relation.

Be noted that though in the present embodiment, common gray scale voltage output circuit 502 and indivedual gray scale voltage output circuit 504 are respectively resistance string, the present invention is not as limit.All any can be according to individual other gamma curve, by the reference voltage output of input and the device of the corresponding gray scale voltage of picture element signal, neitherly take off spirit of the present invention.

Described by preamble, the gamma curve relation of the gray scale voltage of input pixel and the brightness of pixel, meeting changes to some extent along with the difference of the kenel of liquid crystal molecule in the pixel.Gray scale voltage output circuit proposed by the invention also can be made suitable change, has been applicable to multi-form gamma curve.Fig. 7 is the circuit diagram of second kind of gray scale voltage output circuit illustrating according to the preferred embodiments of the present invention.Its gray scale voltage VO64～VO255 is exported by common gray scale voltage output circuit, and is corresponding with picture element signal 64～255 respectively.Red gray scale voltage output circuit, green gray scale voltage output circuit and bluish grey rank voltage follower circuit are then respectively according to gamma curve shown in Figure 8 " R ", " G " reach " B ", export red gray scale voltage VO0r～VO63r, green gray scale voltage VO0g～VO63g and bluish grey rank voltage VO0b～VO63b.These three groups of gray scale voltages are all corresponding with picture element signal 0～63.The gray scale voltage output circuit that Fig. 7 illustrated is applicable to the gamma curve relation that Fig. 8 illustrates.The gray scale voltage output circuit that Fig. 9 illustrated, its indivedual gray scale voltage output circuits are divided into two parts.With red gray scale voltage output circuit is example, it is made up of two resistance string, export red gray scale voltage VO255r～VO191r according to reference voltage V1R～V3R respectively, and export red gray scale voltage VO63r～VO1r, as shown in Figure 9 according to reference voltage V6R～V8R.The gray scale voltage output circuit that Fig. 9 illustrated is applicable to the gamma curve relation that Figure 10 illustrates.In like manner, the gray scale voltage output circuit that illustrates of Figure 11 is applicable to the gamma curve relation that Figure 12 illustrates.And the gray scale voltage output circuit that Figure 13 illustrates is applicable to the gamma curve relation that Figure 14 illustrates.Be noted that, though 5th, the gray scale voltage output circuit shown in 7,9,11 and 13 figure and inequality, and also be applicable to multi-form gamma curve, but its common feature is all the part that the gamma curve at different colours differs greatly, respectively according to the gamma curve of different colours, the value of the gray scale voltage of decision output gray scale voltage output circuit, and with the corresponding relation of picture element signal, make the picture element signal of different colours and pixel intensity connect and be the linear ratio relation.So neither disengaging spirit of the present invention.

The gray scale voltage of gray scale voltage output circuit output can input in the gamma-correction circuit.Wherein, gray scale voltage comprises common gray scale voltage and indivedual gray scale voltage, and indivedual gray scale voltages also comprise red gray scale voltage (VOr), green gray scale voltage (VOg) and bluish grey rank voltages (VOb).Gamma-correction circuit is accepted a picture element signal, carries out gamma correction, output and pixel voltages relevant according to common gray scale voltage and with the corresponding indivedual gray scale voltages of picture element signal.If this picture element signal is in order to control one in order to show the brightness of red pixel, the corresponding relation of this picture element signal and pixel voltage then, according to common gray scale voltage and and the value of red gray scale voltage decide.In like manner, if this picture element signal in order to control the brightness in order to the pixel that shows blueness (green), the corresponding relation of this picture element signal and pixel voltage then decides according to common gray scale voltage and with the value of bluish grey rank voltage (green gray scale voltage).

A kind of gamma correcting device and method that the above embodiment of the present invention disclosed, when carrying out gamma correction, provide the pairing gray scale voltage numeric distribution of the picture element signal of different colours partly identical and other parts are inequality, make the gamma characteristic optimization of RGB three colors, to improve the image display quality of liquid crystal panel.

See also Fig. 1 and Fig. 2, Fig. 1 is the module diagram of liquid crystal indicator first embodiment of the present invention, and Fig. 2 is the look-up table synoptic diagram of liquid crystal indicator shown in Figure 1.This liquid crystal indicator 1 comprises a video signal input terminal 10, a microprocessor (MCU) 11, a control system for screen display 12, a gamma-correction circuit (Gamma Correction Circuit) 13 and one display panels 14.This video signal input terminal 10 is connected to this microprocessor 11, and this control system for screen display 12 is connected to this microprocessor 11, and this microprocessor 11 is connected to this gamma-correction circuit 13, and this gamma-correction circuit 13 is connected to this display panels 14.

This video signal input terminal 10 receives one from the vision signal of external circuit and be transferred to this microprocessor 11.This microprocessor 11 receives this vision signal, and according to this video signal generating one original luma data, should original luma data be transferred to this gamma-correction circuit 13 then.This original luma data is represented the brightness of image of this vision signal.

This gamma-correction circuit 13 comprise a look-up table (Look Up Table, LUT) 130, this look-up table 130 comprises a plurality of basic look-up tables 131.Each basic look-up table 131 corresponding gamma value, and store a plurality of original luma data and a plurality of correction luma data corresponding in each basic look-up table 131 with these a plurality of original luma data.This correction luma data is represented the brightness of image according to the vision signal after the corresponding gamma value correction.These a plurality of basic look-up table 131 stored data all adopt 10 bit compression methods to compress.

This gamma-correction circuit 13 receives the original luma data that this microprocessor 11 is transmitted, and in the basic look-up table that system initialization is set, search the corresponding correction luma data of this original luma data according to this original luma data, export this corrections luma data then and arrive this display panels 14.This display panels 14 shows correspondence image according to the correction luma data that receives.

This control system for screen display 12 comprises an input system (figure does not show) and a screen Control-Menu (figure does not show).The user is by this input system entr screen control command and call this screen Control-Menu.This screen Control-Menu can be presented on this display panels 14, and it is set with one and regulates the gamma option.This adjusting gamma option comprises a gamma range of adjustment.The user calls this screen Control-Menu according to this screen control command, thereby enters this adjusting gamma option, sets or regulate gamma value in this gamma range of adjustment.

When the user reset gamma value by this adjusting gamma option, this control system for screen display 12 sent corresponding control signal according to the gamma value that resets and gives this microprocessor 11.This microprocessor 11 is controlled this gamma-correction circuit 13 according to this control signal the basic look-up table 131 of the gamma value correspondence that resets is set at current look-up table.Simultaneously, this microprocessor 11 receives the current video signal, produces an original luma data and is transferred to this gamma-correction circuit 13.This gamma-correction circuit 13 is searched in this current look-up table correction luma data that should original luma data, and exports this correction luma data to this display panels 14.This display panels 14 is according to the correction luma data display image that receives.

Compared with prior art, because the gamma-correction circuit 13 of liquid crystal indicator 1 of the present invention comprises the basic look-up table 131 of corresponding each gamma value, this control system for screen display 12 is set up one and is regulated the gamma option, make the user reset gamma value by the look-up table function of controlling this gamma-correction circuit 13 according to preference or the selected gamma value of demand.And, because after the user imported gamma value, this gamma-correction circuit 13 only needed the basic look-up table 131 corresponding with the gamma value of user"s input is set at current look-up table, therefore regulates simple fast.Moreover, because it is this gamma-correction circuit 13 carries out gamma correction with the form of basic look-up table 131, therefore accurate to the gamma value adjustment.

The user calls a screen Control-Menu by the input system of this control system for screen display 12, thereby enters the adjusting gamma option of establishing in it, resets a gamma value in this gamma range of adjustment.This control system for screen display 12 correspondingly sends control signal and is transferred to this microprocessor 11.

Step S12 is set at current look-up table and is used for proofreading and correct luma data by the basic look-up table of this gamma-correction circuit 13 with the gamma value correspondence that resets.

This microprocessor 11 is controlled this gamma-correction circuit 13 according to this control signal, and the basic look-up table 131 of the gamma value correspondence that resets is set at current look-up table, is about to the pairing basic look-up table of gamma value that the user sets and is set at current look-up table.This gamma-correction circuit 13 is searched the correction luma data of original luma data correspondence according to the corresponding relation of current look-up table, and outputs to this display panels 14 and come display image, thereby has realized the adjustment of gamma value, and it is more convenient to make the user regulate gamma value.

See also Fig. 4, it is the look-up table synoptic diagram of liquid crystal indicator second embodiment of the present invention.This liquid crystal indicator (figure does not show) is similar to this liquid crystal indicator 1, and its key distinction is: this look-up table 230 comprises a plurality of basic look-up tables 231 and a shared look-up table 232.The corresponding basic look-up table 231 of each gamma value.All gamma values are to sharing look-up table 232.

Because for different gamma values, it is basic identical that the GTG value is not more than 32 pairing a plurality of correction luma data of original luma data, so the GTG value is defined as the first original luma data greater than 32 original luma data, this original luma data that is not more than 32 is defined as the second original luma data.

Each basic look-up table 231 corresponding gamma value, it stores a plurality of first original luma data and a plurality of correction luma data corresponding with this first original luma data under this gamma value.Should share look-up table 232 corresponding each gamma value, it stores a plurality of second original luma data and a plurality of correction luma data corresponding with this second original luma data under this gamma value.The combination of each basic look-up table 231 and shared look-up table 232 stores complete original luma data and the correction luma data corresponding with this original luma data under this gamma value.

After the user reset a gamma value, basic look-up table 231 and shared look-up table 232 that control system for screen display (figure do not show) is controlled the gamma value correspondence that gamma-correction circuit (scheming not show) resets correspondence by microprocessor (figure does not show) were set at current look-up table.Simultaneously, this microprocessor receives the current video signal, produces an original luma data and is transferred to this gamma-correction circuit.This gamma-correction circuit is according to searching in this current look-up table correction luma data that should original luma data, and exports this correction luma data to display panels (scheming not show).This display panels is according to the correction luma data display image that receives.

Compare with first embodiment, because the shared look-up table 232 of this gamma-correction circuit stores the second original luma data of all gamma value correspondences and a plurality of correction luma data of the second original luma data correspondence, therefore save the capacity of storer of store look-up tables of being used for, reduced cost.

The user calls this screen Control-Menu by the input system of this control system for screen display, thereby enters the adjusting gamma option of establishing in it, resets a gamma value in this gamma range of adjustment.This control system for screen display correspondingly sends control signal and is transferred to this microprocessor.

Step S22 is set at current look-up table and is used for proofreading and correct luma data with shared look-up table 232 by the basic look-up table 231 of this gamma-correction circuit with the gamma value correspondence that resets.

This control signal of this microprocessor analysis, and then control this gamma-correction circuit the basic look-up table 231 of the gamma value correspondence that resets is set at current look-up table with shared look-up table 232, be about to the pairing basic look-up table 231 of gamma value that the user sets and be set at current look-up table with shared look-up table 232.This gamma-correction circuit is searched the correction luma data of original luma data correspondence according to the corresponding relation of current look-up table, and outputs to this display panels and come display image.

Liquid crystal indicator of the present invention also can have other numerous variations design, as: this control system for screen display 12 can also be directly connected to this gamma-correction circuit 13, controls this gamma-correction circuit 13 the basic look-up table 131,231 corresponding with the gamma value of input system input is set at current look-up table.

Step back from your monitor and view the above image. The 2.0 patch should appear darker, the 2.4 patch lighter, and the 2.2 patch should blend in with its surroundings. For web use you"ll want a gamma of 2.2, the sRGB standard.

Although the purpose of this image is to verify monitor gamma, it also works well to check display quality at different viewing angles. Step back from your monitor and move up and down. If it"s based on IPS or PLS technology the bars will barely change in color. If it"s based on TN technology the change is quite large. For this reason IPS monitors are recommended for image editing.

QuickGamma is free software based on Norman Koren"s monitor test patterns. Before calibration set monitor color temperature to 6500° and maximum contrast. If you"re calibrating an LCD be sure to read this first.

Have you ever noticed how we tend to miss out on smaller details if the image is really bright? The reason for this is that we are much more sensitive to changes in dark tones than we are to similar changes in bright tones. There’s actually a biological reason for this peculiarity. It happens because it enables our vision to operate over a broader range of luminance. Otherwise, the typical range in brightness we encounter outdoors would be too overwhelming. Our visual system is really smart that way!

We are getting there! The reason we are discussing all this is because we need to understand how we perceive luminance in order to understand why we need gamma correction. Gamma basically establishes a relationship between our eye’s light sensitivity and that of the camera. When a digital image is saved, it’s therefore “gamma encoded”. This way, twice the value in a file more closely corresponds to what we would perceive as being twice as bright.

The reason we do gamma encoding is because gamma encoded images store tones more efficiently. Since gamma encoding redistributes tonal levels closer to how our eyes perceive them, fewer bits are needed to describe a given tonal range. The number of bits you allocate to a particular thing dictates the level of detail you can store about it. Since our visual system doesn’t really care about the details in the brighter regions, we don’t have to waste more number bits to store information about that region. The extra bits that are saved can instead be devoted to describe the darker tones, where the camera is relatively less sensitive.

Image Gamma: This is applied either by your camera or RAW development software. Whenever an image is captured, it is converted into a standard JPEG or TIFF file. So when the camera software does that, it redistributes native camera tonal levels into ones which are more perceptually uniform. This way, we make the most efficient use of a given bit depth. As in, we only have a certain number of bits to represent an image and we need to make the best of it. In order to use it efficiently, our camera software assigns more bits to darker tones and lesser number of bits to the brighter tones.

Display Gamma: This refers to the net influence of your video card and display device. The main purpose of the display gamma is to compensate for a file’s gamma. We need this step because we need to ensure that the image isn’t unrealistically brightened when displayed on your screen. A higher display gamma results in a darker image with greater contrast. You can see this in the image above. The image on the right has a higher gamma, and is therefore brighter.

System Gamma: This represents the net effect of all gamma values that have been applied to an image. The net effect basically refers to the combination of image gamma and display gamma. For faithful reproduction of a scene, this should ideally be close to a straight line (gamma = 1.0). A straight line ensures that the input is same as the output, i.e. the original scene is the same as what’s being displayed on your screen. However, the system gamma is sometimes set slightly greater than 1.0 in order to improve contrast. As we all know, human eye loves contrast!

All the images and videos we view today are viewed on some kind of monitor. So this whole gamma correction thing is an integral part of those monitors.

CRT Monitors: The interesting thing to note is that the native gamma of a CRT is 2.5. This is almost the inverse of our eyes! So technically, values from a gamma-encoded image file could be sent straight to the screen and they would automatically be corrected. The CRT monitors will almost nullify them by default. However, a small gamma correction of 1.1 needs to be applied to achieve an overall display gamma of 2.2. This is usually already set by the manufacturer’s default settings, but can also be set during monitor calibration.

LCD Monitors: LCD monitors have a different gamma value. To achieve an overall display gamma of 2.2, we often need substantial corrections. LCDs therefore require something called a look-up table (LUT) in order to ensure that input values are depicted using the intended display gamma. This is a whole new pandora’s box we cannot afford to open in this blog post!

Basically, gamma correction is yet another piece of puzzle in the world of digital imaging that exists everywhere. Human visual system is a spectacular piece of engineering marvel and every imaging device aspires to replicate it. That’s the reason we dance according to its tune to capture all the subtle nuances and imbibe them in our digital imaging systems!

Your monitor’s gamma tells you its pixels’ luminance at every brightness level, from 0-100%. Lower gamma makes shadows looks brighter and can result in a flatter, washed out image, where it"s harder to see brighter highlights. Higher gamma can make it harder to see details in shadows. Some monitors offer different gamma modes, allowing you to tweak image quality to your preference. The standard for the sRGBcolor space, however, is a value of 2.2.

Gamma is important because it affects the appearance of dark areas, like blacks and shadows and midtones, as well as highlights. Monitors with poor gamma can either crush detail at various points or wash it out, making the entire picture appear flat and dull. Proper gamma leads to more depth and realism and a more three-dimensional image.

The image gallery below (courtesy of BenQ(opens in new tab)) shows an image with the 2.2 gamma standard compared to that same image with low gamma and with high gamma.

Typically, if you are running on the Windows operating system, the most accurate color is achieved with a gamma value of 2.2 (for Mac OS, the ideal gamma value is 1.8). So when testing monitors, we strive for a gamma value of 2.2. A monitor’s range of gamma values indicates how far the lowest and highest values differ from the 2.2 standard (the smaller the difference, the better).

In our monitor reviews, we’ll show you gamma charts like the one above, with the x axis representing different brightness levels. The yellow line represents 2.2 gamma value. The closer the gray line conforms to the yellow line, the better.

Glass substrate with ITO electrodes. The shapes of these electrodes will determine the shapes that will appear when the LCD is switched ON. Vertical ridges etched on the surface are smooth.

A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directlybacklight or reflector to produce images in color or monochrome.seven-segment displays, as in a digital clock, are all good examples of devices with these displays. They use the same basic technology, except that arbitrary images are made from a matrix of small pixels, while other displays have larger elements. LCDs can either be normally on (positive) or off (negative), depending on the polarizer arrangement. For example, a character positive LCD with a backlight will have black lettering on a background that is the color of the backlight, and a character negative LCD will have a black background with the letters being of the same color as the backlight. Optical filters are added to white on blue LCDs to give them their characteristic appearance.

LCDs are used in a wide range of applications, including LCD televisions, computer monitors, instrument panels, aircraft cockpit displays, and indoor and outdoor signage. Small LCD screens are common in LCD projectors and portable consumer devices such as digital cameras, watches, digital clocks, calculators, and mobile telephones, including smartphones. LCD screens are also used on consumer electronics products such as DVD players, video game devices and clocks. LCD screens have replaced heavy, bulky cathode-ray tube (CRT) displays in nearly all applications. LCD screens are available in a wider range of screen sizes than CRT and plasma displays, with LCD screens available in sizes ranging from tiny digital watches to very large television receivers. LCDs are slowly being replaced by OLEDs, which can be easily made into different shapes, and have a lower response time, wider color gamut, virtually infinite color contrast and viewing angles, lower weight for a given display size and a slimmer profile (because OLEDs use a single glass or plastic panel whereas LCDs use two glass panels; the thickness of the panels increases with size but the increase is more noticeable on LCDs) and potentially lower power consumption (as the display is only "on" where needed and there is no backlight). OLEDs, however, are more expensive for a given display size due to the very expensive electroluminescent materials or phosphors that they use. Also due to the use of phosphors, OLEDs suffer from screen burn-in and there is currently no way to recycle OLED displays, whereas LCD panels can be recycled, although the technology required to recycle LCDs is not yet widespread. Attempts to maintain the competitiveness of LCDs are quantum dot displays, marketed as SUHD, QLED or Triluminos, which are displays with blue LED backlighting and a Quantum-dot enhancement film (QDEF) that converts part of the blue light into red and green, offering similar performance to an OLED display at a lower price, but the quantum dot layer that gives these displays their characteristics can not yet be recycled.

Since LCD screens do not use phosphors, they rarely suffer image burn-in when a static image is displayed on a screen for a long time, e.g., the table frame for an airline flight schedule on an indoor sign. LCDs are, however, susceptible to image persistence.battery-powered electronic equipment more efficiently than a CRT can be. By 2008, annual sales of televisions with LCD screens exceeded sales of CRT units worldwide, and the CRT became obsolete for most purposes.

Each pixel of an LCD typically consists of a layer of molecules aligned between two transparent electrodes, often made of Indium-Tin oxide (ITO) and two polarizing filters (parallel and perpendicular polarizers), the axes of transmission of which are (in most of the cases) perpendicular to each other. Without the liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second (crossed) polarizer. Before an electric field is applied, the orientation of the liquid-crystal molecules is determined by the alignment at the surfaces of electrodes. In a twisted nematic (TN) device, the surface alignment directions at the two electrodes are perpendicular to each other, and so the molecules arrange themselves in a helical structure, or twist. This induces the rotation of the polarization of the incident light, and the device appears gray. If the applied voltage is large enough, the liquid crystal molecules in the center of the layer are almost completely untwisted and the polarization of the incident light is not rotated as it passes through the liquid crystal layer. This light will then be mainly polarized perpendicular to the second filter, and thus be blocked and the pixel will appear black. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts thus constituting different levels of gray.

The chemical formula of the liquid crystals used in LCDs may vary. Formulas may be patented.Sharp Corporation. The patent that covered that specific mixture expired.

Most color LCD systems use the same technique, with color filters used to generate red, green, and blue subpixels. The LCD color filters are made with a photolithography process on large glass sheets that are later glued with other glass sheets containing a TFT array, spacers and liquid crystal, creating several color LCDs that are then cut from one another and laminated with polarizer sheets. Red, green, blue and black photoresists (resists) are used. All resists contain a finely ground powdered pigment, with particles being just 40 nanometers across. The black resist is the first to be applied; this will create a black grid (known in the industry as a black matrix) that will separate red, green and blue subpixels from one another, increasing contrast ratios and preventing light from leaking from one subpixel onto other surrounding subpixels.Super-twisted nematic LCD, where the variable twist between tighter-spaced plates causes a varying double refraction birefringence, thus changing the hue.

LCD in a Texas Instruments calculator with top polarizer removed from device and placed on top, such that the top and bottom polarizers are perpendicular. As a result, the colors are inverted.

The optical effect of a TN device in the voltage-on state is far less dependent on variations in the device thickness than that in the voltage-off state. Because of this, TN displays with low information content and no backlighting are usually operated between crossed polarizers such that they appear bright with no voltage (the eye is much more sensitive to variations in the dark state than the bright state). As most of 2010-era LCDs are used in television sets, monitors and smartphones, they have high-resolution matrix arrays of pixels to display arbitrary images using backlighting with a dark background. When no image is displayed, different arrangements are used. For this purpose, TN LCDs are operated between parallel polarizers, whereas IPS LCDs feature crossed polarizers. In many applications IPS LCDs have replaced TN LCDs, particularly in smartphones. Both the liquid crystal material and the alignment layer material contain ionic compounds. If an electric field of one particular polarity is applied for a long period of time, this ionic material is attracted to the surfaces and degrades the device performance. This is avoided either by applying an alternating current or by reversing the polarity of the electric field as the device is addressed (the response of the liquid crystal layer is identical, regardless of the polarity of the applied field).

Displays for a small number of individual digits or fixed symbols (as in digital watches and pocket calculators) can be implemented with independent electrodes for each segment.alphanumeric or variable graphics displays are usually implemented with pixels arranged as a matrix consisting of electrically connected rows on one side of the LC layer and columns on the other side, which makes it possible to address each pixel at the intersections. The general method of matrix addressing consists of sequentially addressing one side of the matrix, for example by selecting the rows one-by-one and applying the picture information on the other side at the columns row-by-row. For details on the various matrix addressing schemes see passive-matrix and active-matrix addressed LCDs.

LCDs, along with OLED displays, are manufactured in cleanrooms borrowing techniques from semiconductor manufacturing and using large sheets of glass whose size has increased over time. Several displays are manufactured at the same time, and then cut from the sheet of glass, also known as the mother glass or LCD glass substrate. The increase in size allows more displays or larger displays to be made, just like with increasing wafer sizes in semiconductor manufacturing. The glass sizes are as follows:

Until Gen 8, manufacturers would not agree on a single mother glass size and as a result, different manufacturers would use slightly different glass sizes for the same generation. Some manufacturers have adopted Gen 8.6 mother glass sheets which are only slightly larger than Gen 8.5, allowing for more 50 and 58 inch LCDs to be made per mother glass, specially 58 inch LCDs, in which case 6 can be produced on a Gen 8.6 mother glass vs only 3 on a Gen 8.5 mother glass, significantly reducing waste.AGC Inc., Corning Inc., and Nippon Electric Glass.

In 1922, Georges Friedel described the structure and properties of liquid crystals and classified them in three types (nematics, smectics and cholesterics). In 1927, Vsevolod Frederiks devised the electrically switched light valve, called the Fréedericksz transition, the essential effect of all LCD technology. In 1936, the Marconi Wireless Telegraph company patented the first practical application of the technology, "The Liquid Crystal Light Valve". In 1962, the first major English language publication Molecular Structure and Properties of Liquid Crystals was published by Dr. George W. Gray.RCA found that liquid crystals had some interesting electro-optic characteristics and he realized an electro-optical effect by generating stripe-patterns in a thin layer of liquid crystal material by the application of a voltage. This effect is based on an electro-hydrodynamic instability forming what are now called "Williams domains" inside the liquid crystal.

In the late 1960s, pioneering work on liquid crystals was undertaken by the UK"s Royal Radar Establishment at Malvern, England. The team at RRE supported ongoing work by George William Gray and his team at the University of Hull who ultimately discovered the cyanobiphenyl liquid crystals, which had correct stability and temperature properties for application in LCDs.

The idea of a TFT-based liquid-crystal display (LCD) was conceived by Bernard Lechner of RCA Laboratories in 1968.dynamic scattering mode (DSM) LCD that used standard discrete MOSFETs.

On December 4, 1970, the twisted nematic field effect (TN) in liquid crystals was filed for patent by Hoffmann-LaRoche in Switzerland, (Swiss patent No. 532 261) with Wolfgang Helfrich and Martin Schadt (then working for the Central Research Laboratories) listed as inventors.Brown, Boveri & Cie, its joint venture partner at that time, which produced TN displays for wristwatches and other applications during the 1970s for the international markets including the Japanese electronics industry, which soon produced the first digital quartz wristwatches with TN-LCDs and numerous other products. James Fergason, while working with Sardari Arora and Alfred Saupe at Kent State University Liquid Crystal Institute, filed an identical patent in the United States on April 22, 1971.ILIXCO (now LXD Incorporated), produced LCDs based on the TN-effect, which soon superseded the poor-quality DSM types due to improvements of lower operating voltages and lower power consumption. Tetsuro Hama and Izuhiko Nishimura of Seiko received a US patent dated February 1971, for an electronic wristwatch incorporating a TN-LCD.

In 1972, the concept of the active-matrix thin-film transistor (TFT) liquid-crystal display panel was prototyped in the United States by T. Peter Brody"s team at Westinghouse, in Pittsburgh, Pennsylvania.Westinghouse Research Laboratories demonstrated the first thin-film-transistor liquid-crystal display (TFT LCD).high-resolution and high-quality electronic visual display devices use TFT-based active matrix displays.active-matrix liquid-crystal display (AM LCD) in 1974, and then Brody coined the term "active matrix" in 1975.

In 1972 North American Rockwell Microelectronics Corp introduced the use of DSM LCDs for calculators for marketing by Lloyds Electronics Inc, though these required an internal light source for illumination.Sharp Corporation followed with DSM LCDs for pocket-sized calculators in 1973Seiko and its first 6-digit TN-LCD quartz wristwatch, and Casio"s "Casiotron". Color LCDs based on Guest-Host interaction were invented by a team at RCA in 1968.TFT LCDs similar to the prototypes developed by a Westinghouse team in 1972 were patented in 1976 by a team at Sharp consisting of Fumiaki Funada, Masataka Matsuura, and Tomio Wada,

In 1983, researchers at Brown, Boveri & Cie (BBC) Research Center, Switzerland, invented the passive matrix-addressed LCDs. H. Amstutz et al. were listed as inventors in the corresponding patent applications filed in Switzerland on July 7, 1983, and October 28, 1983. Patents were granted in Switzerland CH 665491, Europe EP 0131216,

The first color LCD televisions were developed as handheld televisions in Japan. In 1980, Hattori Seiko"s R&D group began development on color LCD pocket televisions.Seiko Epson released the first LCD television, the Epson TV Watch, a wristwatch equipped with a small active-matrix LCD television.dot matrix TN-LCD in 1983.Citizen Watch,TFT LCD.computer monitors and LCD televisions.3LCD projection technology in the 1980s, and licensed it for use in projectors in 1988.compact, full-color LCD projector.

In 1990, under different titles, inventors conceived electro optical effects as alternatives to twisted nematic field effect LCDs (TN- and STN- LCDs). One approach was to use interdigital electrodes on one glass substrate only to produce an electric field essentially parallel to the glass substrates.Germany by Guenter Baur et al. and patented in various countries.Hitachi work out various practical details of the IPS technology to interconnect the thin-film transistor array as a matrix and to avoid undesirable stray fields in between pixels.

Hitachi also improved the viewing angle dependence further by optimizing the shape of the electrodes (Super IPS). NEC and Hitachi become early manufacturers of active-matrix addressed LCDs based on the IPS technology. This is a milestone for implementing large-screen LCDs having acceptable visual performance for flat-panel computer monitors and television screens. In 1996, Samsung developed the optical patterning technique that enables multi-domain LCD. Multi-domain and In Plane Switching subsequently remain the dominant LCD designs through 2006.South Korea and Taiwan,

In 2007 the image quality of LCD televisions surpassed the image quality of cathode-ray-tube-based (CRT) TVs.LCD TVs were projected to account 50% of the 200 million TVs to be shipped globally in 2006, according to Displaybank.Toshiba announced 2560 × 1600 pixels on a 6.1-inch (155 mm) LCD panel, suitable for use in a tablet computer,transparent and flexible, but they cannot emit light without a backlight like OLED and microLED, which are other technologies that can also be made flexible and transparent.

In 2016, Panasonic developed IPS LCDs with a contrast ratio of 1,000,000:1, rivaling OLEDs. This technology was later put into mass production as dual layer, dual panel or LMCL (Light Modulating Cell Layer) LCDs. The technology uses 2 liquid crystal layers instead of one, and may be used along with a mini-LED backlight and quantum dot sheets.

Since LCDs produce no light of their own, they require external light to produce a visible image.backlight. Active-matrix LCDs are almost always backlit.Transflective LCDs combine the features of a backlit transmissive display and a reflective display.

CCFL: The LCD panel is lit either by two cold cathode fluorescent lamps placed at opposite edges of the display or an array of parallel CCFLs behind larger displays. A diffuser (made of PMMA acrylic plastic, also known as a wave or light guide/guiding plateinverter to convert whatever DC voltage the device uses (usually 5 or 12 V) to ≈1000 V needed to light a CCFL.

EL-WLED: The LCD panel is lit by a row of white LEDs placed at one or more edges of the screen. A light diffuser (light guide plate, LGP) is then used to spread the light evenly across the whole display, similarly to edge-lit CCFL LCD backlights. The diffuser is made out of either PMMA plastic or special glass, PMMA is used in most cases because it is rugged, while special glass is used when the thickness of the LCD is of primary concern, because it doesn"t expand as much when heated or exposed to moisture, which allows LCDs to be just 5mm thick. Quantum dots may be placed on top of the diffuser as a quantum dot enhancement film (QDEF, in which case they need a layer to be protected from heat and humidity) or on the color filter of the LCD, replacing the resists that are normally used.

WLED array: The LCD panel is lit by a full array of white LEDs placed behind a diffuser behind the panel. LCDs that use this implementation will usually have the ability to dim or completely turn off the LEDs in the dark areas of the image being displayed, effectively increasing the contrast ratio of the display. The precision with which this can be done will depend on the number of dimming zones of the display. The more dimming zones, the more precise the dimming, with less obvious blooming artifacts which are visible as dark grey patches surrounded by the unlit areas of the LCD. As of 2012, this design gets most of its use from upscale, larger-screen LCD televisions.

RGB-LED array: Similar to the WLED array, except the panel is lit by a full array of RGB LEDs. While displays lit with white LEDs usually have a poorer color gamut than CCFL lit displays, panels lit with RGB LEDs have very wide color gamuts. This implementation is most popular on professional graphics editing LCDs. As of 2012, LCDs in this category usually cost more than $1000. As of 2016 the cost of this category has drastically reduced and such LCD televisions obtained same price levels as the former 28" (71 cm) CRT based categories.

Monochrome LEDs: such as red, green, yellow or blue LEDs are used in the small passive monochrome LCDs typically used in clocks, watches and small appliances.

Today, most LCD screens are being designed with an LED backlight instead of the traditional CCFL backlight, while that backlight is dynamically controlled with the video information (dynamic backlight control). The combination with the dynamic backlight control, invented by Philips researchers Douglas Stanton, Martinus Stroomer and Adrianus de Vaan, simultaneously increases the dynamic range of the display system (also marketed as HDR, high dynamic range television or FLAD, full-area local area dimming).

The LCD backlight systems are made highly efficient by applying optical films such as prismatic structure (prism sheet) to gain the light into the desired viewer directions and reflective polarizing films that recycle the polarized light that was formerly absorbed by the first polarizer of the LCD (invented by Philips researchers Adrianus de Vaan and Paulus Schaareman),

Due to the LCD layer that generates the desired high resolution images at flashing video speeds using very low power electronics in combination with LED based backlight technologies, LCD technology has become the dominant display technology for products such as televisions, desktop monitors, notebooks, tablets, smartphones and mobile phones. Although competing OLED technology is pushed to the market, such OLED displays do not feature the HDR capabilities like LCDs in combination with 2D LED backlight technologies have, reason why the annual market of such LCD-based products is still growing faster (in volume) than OLED-based products while the efficiency of LCDs (and products like portable computers, mobile phones and televisions) may even be further improved by preventing the light to be absorbed in the colour filters of the LCD.

A pink elastomeric connector mating an LCD panel to circuit board traces, shown next to a centimeter-scale ruler. The conductive and insulating layers in the black stripe are very small.

A standard television receiver screen, a modern LCD panel, has over six million pixels, and they are all individually powered by a wire network embedded in the screen. The fine wires, or pathways, form a grid with vertical wires across the whole screen on one side of the screen and horizontal wires across the whole screen on the other side of the screen. To this grid each pixel has a positive connection on one side and a negative connection on the other side. So the total amount of wires needed for a 1080p display is 3 x 1920 going vertically and 1080 going horizontally for a total of 6840 wires horizontally and vertically. That"s three for red, green and blue and 1920 columns of pixels for each color for a total of 5760 wires going vertically and 1080 rows of wires going horizontally. For a panel that is 28.8 inches (73 centimeters) wide, that means a wire density of 200 wires per inch along the horizontal edge.

The LCD panel is powered by LCD drivers that are carefully matched up with the edge of the LCD panel at the factory level. The drivers may be installed using several methods, the most common of which are COG (Chip-On-Glass) and TAB (Tape-automated bonding) These same principles apply also for smartphone screens that are much smaller than TV screens.anisotropic conductive film or, for lower densities, elastomeric connectors.

Monochrome and later color passive-matrix LCDs were standard in most early laptops (although a few used plasma displaysGame Boyactive-matrix became standard on all laptops. The commercially unsuccessful Macintosh Portable (released in 1989) was one of the first to use an ac