Gamma Panel is a tool that will allow you to adjust in real time the brightness, the contrast and the gamma of your computer´s screen. To obtain the desired configuration, the user only have to slide the adjustment bars to the left or to the right.
Gamma Control is an easy to use software designed to let you adjust the gamma on your computer, by just pressing a combination of keys on your keyboard, and/or mouse. Or you can adjust the gamma levels by using a trackbar. Control DLC The Foundation - The Nail - Research Site Gamma - Complete the Ritual in the Deep Cavern.
UNDERSTANDING GAMMA CORRECTION. Gamma is an important but seldom understood characteristic of virtually all digital imaging systems. It defines the relationship between a pixel's numerical value and its actual luminance. Without gamma, shades captured by digital cameras wouldn't appear as they did to our eyes (on a standard monitor). Oct 16, 2016 Gamma Panel is a little & handy application that lets you adjust brightness, contrast and gamma settings in real-time. Thanks to its hot-key feature, you don't even have to leave the game you're playing!
Gamma is an important but seldom understood characteristic of virtually all digital imaging systems. It defines the relationship between a pixel's numerical value and its actual luminance. Without gamma, shades captured by digital cameras wouldn't appear as they did to our eyes (on a standard monitor). It's also referred to as gamma correction, gamma encoding or gamma compression, but these all refer to a similar concept. Understanding how gamma works can improve one's exposure technique, in addition to helping one make the most of image editing.
WHY GAMMA IS USEFUL
1. Our eyes do not perceive light the way cameras do. With a digital camera, when twice the number of photons hit the sensor, it receives twice the signal (a 'linear' relationship). Pretty logical, right? That's not how our eyes work. Instead, we perceive twice the light as being only a fraction brighter — and increasingly so for higher light intensities (a 'nonlinear' relationship).
Reference Tone
Select:| Perceived as 50% as Bright by Our Eyes |
| Detected as 50% as Bright by the Camera |
Refer to the tutorial on the photoshop curves tool if you're having trouble interpreting the graph.
Accuracy of comparison depends on having a well-calibrated monitor set to a display gamma of 2.2.
Actual perception will depend on viewing conditions, and may be affected by other nearby tones.
For extremely dim scenes, such as under starlight, our eyes begin to see linearly like cameras do.
Compared to a camera, we are much more sensitive to changes in dark tones than we are to similar changes in bright tones. There's a biological reason for this peculiarity: 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.
But how does all of this relate to gamma? In this case, gamma is what translates between our eye's light sensitivity and that of the camera. When a digital image is saved, it's therefore 'gamma encoded' — so that twice the value in a file more closely corresponds to what we would perceive as being twice as bright.
Technical Note: Gamma is defined by Vout = Vingamma , where Vout is the output luminance value and Vin is the input/actual luminance value. This formula causes the blue line above to curve. When gamma<1, the line arches upward, whereas the opposite occurs with gamma>1.
2. 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. Otherwise, an excess of bits would be devoted to describe the brighter tones (where the camera is relatively more sensitive), and a shortage of bits would be left to describe the darker tones (where the camera is relatively less sensitive):
Note: Above gamma encoded gradient shown using a standard value of 1/2.2
See the tutorial on bit depth for a background on the relationship between levels and bits.
Notice how the linear encoding uses insufficient levels to describe the dark tones — even though this leads to an excess of levels to describe the bright tones. On the other hand, the gamma encoded gradient distributes the tones roughly evenly across the entire range ('perceptually uniform'). This also ensures that subsequent image editing, color and histograms are all based on natural, perceptually uniform tones.
However, real-world images typically have at least 256 levels (8 bits), which is enough to make tones appear smooth and continuous in a print. If linear encoding were used instead, 8X as many levels (11 bits) would've been required to avoid image posterization.
GAMMA WORKFLOW: ENCODING & CORRECTION
Despite all of these benefits, gamma encoding adds a layer of complexity to the whole process of recording and displaying images. The next step is where most people get confused, so take this part slowly. A gamma encoded image has to have 'gamma correction' applied when it is viewed — which effectively converts it back into light from the original scene. In other words, the purpose of gamma encoding is for recording the image — not for displaying the image. Fortunately this second step (the 'display gamma') is automatically performed by your monitor and video card. The following diagram illustrates how all of this fits together:
is Saved as a JPEG File1. Image File Gamma
on a Computer Monitor2. Display Gamma
1. Depicts an image in the sRGB color space (which encodes using a gamma of approx. 1/2.2).
2. Depicts a display gamma equal to the standard of 2.2
1. Image Gamma. This is applied either by your camera or RAW development software whenever a captured image is converted into a standard JPEG or TIFF file. It redistributes native camera tonal levels into ones which are more perceptually uniform, thereby making the most efficient use of a given bit depth.
2. Display Gamma. This refers to the net influence of your video card and display device, so it may in fact be comprised of several gammas. The main purpose of the display gamma is to compensate for a file's gamma — thereby ensuring that the image isn't unrealistically brightened when displayed on your screen. A higher display gamma results in a darker image with greater contrast.
3. System Gamma. This represents the net effect of all gamma values that have been applied to an image, and is also referred to as the 'viewing 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 (the original scene) is the same as the output (the light displayed on your screen or in a print). However, the system gamma is sometimes set slightly greater than 1.0 in order to improve contrast. This can help compensate for limitations due to the dynamic range of a display device, or due to non-ideal viewing conditions and image flare.
IMAGE FILE GAMMA
The precise image gamma is usually specified by a color profile that is embedded within the file. Most image files use an encoding gamma of 1/2.2 (such as those using sRGB and Adobe RGB 1998 color), but the big exception is with RAW files, which use a linear gamma. However, RAW image viewers typically show these presuming a standard encoding gamma of 1/2.2, since they would otherwise appear too dark:
If no color profile is embedded, then a standard gamma of 1/2.2 is usually assumed. Files without an embedded color profile typically include many PNG and GIF files, in addition to some JPEG images that were created using a 'save for the web' setting.
Technical Note on Camera Gamma. Most digital cameras record light linearly, so their gamma is assumed to be 1.0, but near the extreme shadows and highlights this may not hold true. In that case, the file gamma may represent a combination of the encoding gamma and the camera's gamma. However, the camera's gamma is usually negligible by comparison. Camera manufacturers might also apply subtle tonal curves, which can also impact a file's gamma.
DISPLAY GAMMA
This is the gamma that you are controlling when you perform monitor calibration and adjust your contrast setting. Fortunately, the industry has converged on a standard display gamma of 2.2, so one doesn't need to worry about the pros/cons of different values. Older macintosh computers used a display gamma of 1.8, which made non-mac images appear brighter relative to a typical PC, but this is no longer the case.
Recall that the display gamma compensates for the image file's gamma, and that the net result of this compensation is the system/overall gamma. For a standard gamma encoded image file (—), changing the display gamma (—) will therefore have the following overall impact (—) on an image:
Diagrams assume that your display has been calibrated to a standard gamma of 2.2.
Recall from before that the image file gamma (—) plus the display gamma (—) equals the overall system gamma (—). Also note how higher gamma values cause the red curve to bend downward.
If you're having trouble following the above charts, don't despair! It's a good idea to first have an understanding of how tonal curves impact image brightness and contrast. Otherwise you can just look at the portrait images for a qualitative understanding.
How to interpret the charts. The first picture (far left) gets brightened substantially because the image gamma (—) is uncorrected by the display gamma (—), resulting in an overall system gamma (—) that curves upward. In the second picture, the display gamma doesn't fully correct for the image file gamma, resulting in an overall system gamma that still curves upward a little (and therefore still brightens the image slightly). In the third picture, the display gamma exactly corrects the image gamma, resulting in an overall linear system gamma. Finally, in the fourth picture the display gamma over-compensates for the image gamma, resulting in an overall system gamma that curves downward (thereby darkening the image).
The overall display gamma is actually comprised of (i) the native monitor/LCD gamma and (ii) any gamma corrections applied within the display itself or by the video card. However, the effect of each is highly dependent on the type of display device.
CRT Monitors. Due to an odd bit of engineering luck, the native gamma of a CRT is 2.5 — almost the inverse of our eyes. Values from a gamma-encoded file could therefore be sent straight to the screen and they would automatically be corrected and appear nearly OK. However, a small gamma correction of ~1/1.1 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 weren't so fortunate; ensuring an overall display gamma of 2.2 often requires substantial corrections, and they are also much less consistent than CRT's. LCDs therefore require something called a look-up table (LUT) in order to ensure that input values are depicted using the intended display gamma (amongst other things). See the tutorial on monitor calibration: look-up tables for more on this topic.
Technical Note: The display gamma can be a little confusing because this term is often used interchangeably with gamma correction, since it corrects for the file gamma. However, the values given for each are not always equivalent. Gamma correction is sometimes specified in terms of the encoding gamma that it aims to compensate for — not the actual gamma that is applied. For example, the actual gamma applied with a 'gamma correction of 1.5' is often equal to 1/1.5, since a gamma of 1/1.5 cancels a gamma of 1.5 (1.5 * 1/1.5 = 1.0). A higher gamma correction value might therefore brighten the image (the opposite of a higher display gamma).
OTHER NOTES & FURTHER READING
Other important points and clarifications are listed below.
- Dynamic Range. In addition to ensuring the efficient use of image data, gamma encoding also actually increases the recordable dynamic range for a given bit depth. Gamma can sometimes also help a display/printer manage its limited dynamic range (compared to the original scene) by improving image contrast.
- Gamma Correction. The term 'gamma correction' is really just a catch-all phrase for when gamma is applied to offset some other earlier gamma. One should therefore probably avoid using this term if the specific gamma type can be referred to instead.
- Gamma Compression & Expansion. These terms refer to situations where the gamma being applied is less than or greater than one, respectively. A file gamma could therefore be considered gamma compression, whereas a display gamma could be considered gamma expansion.
- Applicability. Strictly speaking, gamma refers to a tonal curve which follows a simple power law (where Vout = Vingamma), but it's often used to describe other tonal curves. For example, the sRGB color space is actually linear at very low luminosity, but then follows a curve at higher luminosity values. Neither the curve nor the linear region follow a standard gamma power law, but the overall gamma is approximated as 2.2.
- Is Gamma Required? No, linear gamma (RAW) images would still appear as our eyes saw them — but only if these images were shown on a linear gamma display. However, this would negate gamma's ability to efficiently record tonal levels.
For more on this topic, also visit the following tutorials:
- Digital Exposure Techniques: Expose to the Right, Clipping & Noise
Learn why gamma and linear RAW files influence a photo's optimal exposure. - How to Calibrate Your Monitor Calibration for Photography
Learn how to accurately set your computer's display gamma.
Gamma correction, or gamma for short, is the name of a nonlinear operation that systems use to code and decode pixel values in images.
What is gamma and what is it for?
At the end of the graphics pipeline, just where the image leaves the computer to make its journey along the monitor cable, there is a small piece of hardware that can transform pixel values on the fly. This hardware typically uses a lookup table to transform the pixels. This hardware uses the red, green and blue values that come from the surface to be displayed to look up gamma-corrected values in the table and then sends the corrected values to the monitor instead of the actual surface values. So, this lookup table is an opportunity to replace any color with any other color. While the table has that level of power, the typical usage is to tweak images subtly to compensate for differences in the monitor’s response. The monitor’s response is the function that relates the numerical value of the red, green and blue components of a pixel with that pixel’s displayed brightness.
That’s what this table was intended for, but game developers found creative uses for it, such as flashing the whole screen red for psychological effect. In modern game apps, as part of the post-processing of each frame, we typically provide other ways to do such things. In fact, we recommend that you leave the gamma table alone because it might be in use to calibrate the monitor’s response, and wholesale changes to the gamma ramp will destroy this careful calibration.
The science of determining gamma correction is complex, and is not presented here, other than to illuminate where the name “gamma” came from. A CRT (that is, an old-fashioned glass) monitor’s response is a complex function, but the physics of these monitors mean that they exhibit a response that can be crudely represented by this power function:
brightness( input ) = inputgamma
The gamma value is typically close to a value of 2.0. LCD monitors and all other newer technologies are specifically engineered to exhibit a similar response so all our software and images don’t have to be recalibrated for those new technologies. The sRGB standard declares that this gamma value is exactly 2.2, and this value has become a widely implemented standard.
The human eye also has a response function which approximately inverts the CRT power function. This means that the perceived brightness of a pixel goes up very roughly linearly with the RGB values in that pixel.
Because a gamma value of 2.2 has become a de-facto standard, we typically don’t need to worry too much about the gamma curve encoded in this table, and can leave it as a linear, one-to-one mapping. Proper color matching does of course require exquisite care with this function, but that discussion is beyond the scope of this topic. Windows includes a tool that lets users calibrate their displays to gamma 2.2, and this tool uses the lookup table hardware to derive a carefully-chosen subtle tweak for their computers. Users can run this tool by searching for 'calibrate color'. There are also well-defined color profiles for particular monitors that automate this process. The 'calibrate color' tool can detect these newer monitors, and inform users that calibration is already in place.
This notion of encoding a power law into color values is useful elsewhere in the graphics pipeline too, especially in textures. For textures, you want more precision on darker colors because of the logarithmic human eye response we just talked about. Careful handling of gamma in this part of the pipeline is important. For more info, see Converting data for the color space.
The remainder of this topic focuses only on gamma correction in this last part of the pipeline, between the frame buffer data and the monitor. If you want to write a calibration wizard or to create special effects in a full-screen app where a post-processing step is not practical, here is the info you need.
Background of gamma on Windows
Windows computers typically have a gamma table that is a lookup table that takes a triplet of bytes and outputs a triplet of bytes. These triplets are 768 (256 x 3) bytes of RAM. This is fine when your display format contains a triplet of RGB BYTE values but isn't expressive enough to describe the transformations that you might want when the display format has a greater range than [0,1], such as floating point values. The APIs in Windows that control gamma have followed an evolution as display formats have become more complex.
The first Windows APIs to offer gamma control are Windows Graphics Device Interface (GDI)’s SetDeviceGammaRamp and GetDeviceGammaRamp. These APIs work with three 256-entry arrays of WORDs, with each WORD encoding zero up to one, represented by WORD values 0 and 65535. The extra precision of a WORD typically isn’t available in actual hardware lookup tables, but these APIs were intended to be flexible. These APIs, in contrast to the others described later in this section, allow only a small deviation from an identity function. In fact, any entry in the ramp must be within 32768 of the identity value. This restriction means that no app can turn the display completely black or to some other unreadable color.
The next API is Microsoft Direct3D 9’s SetGammaRamp, which follows the same pattern and data format as SetDeviceGammaRamp. The default value of the Direct3D 9 gamma ramp is not particularly useful; it is a ramp of WORDs initialized to 0-255, not 0-65535, even though the API is defined in terms of 0-65535.
The latest API is IDXGIOutput::SetGammaControl. This API has a more flexible scheme to express gamma control, as befits DXGI’s increased set of display formats, including ten integer bits-per-channel, 16-bit float formats and the XR_BIAS extended range format.
All of these APIs operate on the same hardware, and change the same values. The Direct3D 9 and DXGI APIs are “write only”. You can't read the value of the hardware, modify it, and then set it. You can only set the ramp. Furthermore, you can only set gamma when the app is full screen. This restriction is another way to guarantee that the desktop is always readable. That is, the app can disturb its own display, but Windows will restore the previous gamma ramp when the app loses full screen (for example, via alt-tab or ctrl-alt-del).
Evolution of display hardware
Some newer monitors can display a wide range of intensities. But, when the display format can represent only values between zero and one, the display must map zero to its darkest value and one to its brightest value. This brightest value might be far too bright for comfortable viewing of Web pages with black text on a white background but is wonderful for over-bright special effects, such as viewing sunlight glittering off of a lake or lightning forking the sky. So, we need a way to express these wider ranges. DXGI 1.1 and later contains display format values that let 1.0 represent a comfortable white value and reserves wider display format values for over-bright special effects. DXGI 1.1 supports two display formats that can express these wider values: DXGI_FORMAT_R10G10B10_XR_BIAS_A2_UNORM and 16-bit floating point. For a full discussion of these formats, see Details of the Extended Format. Next, we look at why DXGI’s IDXGIOutput::SetGammaControl gamma API needs pixel values greater than 1.0.
Gamma control capabilities in DXGI
DXGI lets the display driver express its gamma controls as a step-wise linear function. This step-wise linear function is defined by the control points of this function, the range of values the function can convert to, and an additional optional scale-and-offset operation that can be applied after conversion. An app can call the IDXGIOutput::GetGammaControlCapabilities method to retrieve all of these control capabilities in the DXGI_GAMMA_CONTROL_CAPABILITIES structure.
This graph shows a linear function with just four control points.
DXGI defines control points by their location along the surface color axis. In the preceding graph, the locations of the control points are 0, 0.5, 0.75 and 1.0. These control points indicate that the hardware can convert values in the range 0 through 1.0. DXGI lists these control points in the ControlPointPositions array member of DXGI_GAMMA_CONTROL_CAPABILITIES and always declares them in increasing order. DXGI fills only the first elements of the ControlPointPositions array and indicates the number of elements with the NumGammaControlPoints member of DXGI_GAMMA_CONTROL_CAPABILITIES. If NumGammaControlPoints is less than 1025, DXGI leaves the rest of the ControlPointPositions elements undefined.
The hardware represented by this graph can convert values to a range of 0 through 1.25. So, DXGI sets the MinConvertedValue and MaxConvertedValue members to 0.0f and 1.25f respectively.
DXGI sets the ScaleAndOffsetSupported member of DXGI_GAMMA_CONTROL_CAPABILITIES to indicate whether the hardware supports the scale-and-offset capability. If hardware supports scale-and-offset, it keeps a simple one-to-one lookup table but then adjusts the output of the table to stretch the output to a range greater than [0,1]. The hardware first scales the values that come out of the lookup table and then offsets them.
Note
Different monitors connected to the same computer might have different gamma control capabilities. Moreover, the gamma control capabilities can in fact change depending on the display mode of the output. Consequently, we recommend that you always call IDXGIOutput::GetGammaControlCapabilities to query gamma control capabilities after your app enters full-screen mode.
You can use these gamma control capability values to derive control values that you can then set by using the IDXGIOutput::SetGammaControl API.
Setting gamma control with DXGI
To set gamma controls, you pass a pointer to a DXGI_GAMMA_CONTROL structure when you call the IDXGIOutput::SetGammaControl API.
You set the Scale and Offset members of DXGI_GAMMA_CONTROL to specify the scale and offset values that you want the hardware to apply to the values that you get from the lookup table. You can safely set Scale to 1 and Offset to zero (that is, a scale by one has no effect and an offset of zero has no effect) if you don't want to use the scale-and-offset capability or if the hardware doesn't have that capability.
You set the GammaCurve array member of DXGI_GAMMA_CONTROL to a list of DXGI_RGB structures for the points on the gamma curve. Each DXGI_RGB element specifies the float values that represent the red, green, and blue components for that point. The gamma curve doesn't use alpha values. You use the number that you obtained from NumGammaControlPoints of DXGI_GAMMA_CONTROL_CAPABILITIES to fill that number of elements in the GammaCurve array. Each element that you place in the GammaCurve array is the height for each control point.
Notice in the preceding graph that you now have control over the vertical placement of each control point, and you have separate control for red, green and blue. For example, you can set all of the green and blue values to zero and set the red values to an ascending staircase from zero to one. In this scenario, the displayed image shows only its red parts, with the blue and green appearing as black. You can also set a descending staircase for all colors, which results in an inverted display. Any value you place in the GammaCurve array must be inclusively within the values you obtained from the MinConvertedValue and MaxConvertedValue members of DXGI_GAMMA_CONTROL_CAPABILITIES.
Gamma control practicalities
DXGI’s gamma controls apply only as long as the app is full screen. Windows restores the previous state of the display when the app exits or returns to windowed mode. But Windows doesn’t restore your app’s gamma state if the app re-enters full-screen mode. Your app must explicitly restore its gamma state when it re-enters full-screen mode.
Not all adapters support gamma control. If an adapter doesn't support gamma control, it ignores calls to set a gamma ramp.
Apps that run under remote desktop can't control gamma at all.
Gamma Control Rust
The mouse cursor, if it is implemented in hardware (as most are), typically doesn't respond to the gamma setting.
Gamma Control 4
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