# Tag Info

## Hot answers tagged gamma

15

Yes, while many screens and OS operations are using a gamma of 2.2 your hardware and computation result still need to be corrected. There are also special mediums such as broadcast TV's that have a different gamma. Sensor equipment like cameras are mostly linear so they need to be adjusted accordingly. Besides this the user can set their system to whatever ...

13

We know that in PNG,BMP,etc... the pixel value stored is not in the linear RGB space. This is not necessarily true. You can store whatever color space you want into an image, it doesn't even need to be colors (such as normal maps). The alpha channel is generally linear. The alpha channel doesn't get displayed, but it is generally a non-color term used for ...

12

What the video is talking about is called gamma correction and it's a very familiar topic for graphics programmers. The first 30 minutes of John Hable's talk on Uncharted 2 rendering is my favorite introduction to "why graphics programmers should care about gamma", as well as being a good introduction to HDR rendering. If you don't want to watch ...

11

The de facto standard color space for digital images these days is sRGB. sRGB is a good default assumption if working with a display whose exact color space is not known (i.e. most random displays someone might run your app on), or images whose color space encoding is not known (i.e. most random image files you might encounter). The sRGB standard defines ...

7

Yes, your theory is correct. A gamma-correct blur entails converting the input pixels to linear color space, performing the blur weighting and accumulation in that space, and then converting back to gamma space at the end. As noted in the comments, the actual transform is not literally squaring and square-rooting, that's just an approximation (and not that ...

7

The short answer is "no", for reasons covered in Alvy Ray Smith's memo, Gamma Correction. Gamma is not about nonlinearity in human perception, it's about nonlinearity in display devices (and, I suppose, acquisition devices too).

6

If I get correctly what you are asking you basically just need to find the G in this equation: $$Image_{out} = Image_{in}^G$$ This could be easily solved as $$G = \frac{\log{Image_{out}}}{\log{Image_{in}}}$$ Because usually gamma is applied in a uniform fashion on the image, you can just pick any two non zero pixel values (one for source and one for ...

6

Short answer, set the precision of the image to a higher value. Long answer, When looking at a gamma correction curve, you can see that the lower values get changed much more, this means that the difference between lower values will get greater and that causes this effect. You have a limited amount of values for a color channel and this means that when it ...

6

Is every image from the internet commonly got gamma corrected? Every image is encoded with a color profile. Most color profiles do have a gamma correction, but not every color profile has that (raw for example). Most images on the internet are encoded in sRGB, which is gamma corrected. If you would download a random image from the internet, you will more ...

5

I think it would be a good idea to get back to the basics. It's a large post, so there's a recap at the end. Colour can be represented in a couple of ways. We can have Red, Green and Blue (RGB). We could have CMYK (used in printing). There's also YCbCr/YUV (one for luminance and two for colour) and similar flavours of that. We have HSV/HSL/HSB (hue, ...

5

The fact that a photo is stored in gamma space doesn't have to do with PNG or JPEG, it has to do with the fact that it's a photo. The camera detects a 50% intensity but is going to save it as a 187 instead of 127, because that is more efficient to keep the color information that matters to the human eye when you have only 256 different possible values. And ...

4

In short: You should not gamma correct your glow map. In fact, you should do everything in a linear color space. At the very end, when doing any color grading (which is the very last step), you convert the final image to the right color space. The color space include that gamma correction. In long: Gamma correction is a step in the encoding of images. It ...

4

I have found the issue. The gamma correction was the correct value, the same as in the book (1/2), but the light source had the brightness of 1.0f. The book had set the light's brightness to 18.0f for all color channels. This would introduce color overflow if left at that, and the very light areas (above 1.0f, and subsequently when converted, outside the ...

3

The actual color of a pixel, outputted on a monitor, does not linearly depend on the applied voltage signal for that pixel. For CRT monitors, the actual color is approximately proportional to the applied voltage raised to the power of a so-called gamma value, which depends on the monitor. This gamma value typically lies between 2.2 and 2.5 for CRT monitors. (...

3

This has to do with gamma correction. If one pixel has red component with value of 1 (where 255 is max), the next pixel has value for red that is 2, there no guarantee that exactly twice as much photons are exiting from the second pixel. Displays have different curves that predict what's the expected brightness. It also has to do with how our eyes work: ...

3

Introduction It depends on how you create the map! Consider the following and let it sink in for a while before you go forward: The image is displayed with a gamma correction for the benefit of your eyes The data is still just data. The gamma correction is for the display part not the data part. Now a bump map is pretty hard to draw with a paint ...

3

JPG, PNG or any other 8 bit image formats do not intrinsically have 1/2.2 gamma associated with it. They just store values from 0-255. How that data is interpreted depends on the software that reads and writes those files. The interesting fact is that most image editing software uses gamma color space by default. All the brushes, effects, filters and even ...

3

Actually, if your bump or displacement map is saved with that 0.45 gamma correction, it's wrong. These maps contain geometrical information rather than colour, and as such, should be simply encoded linearly. For a related issue and a fix for Adobe Photoshop, see this slide deck: https://docs.google.com/presentation/d/1vS5nAAnXbZ8Pt6-dXxy-...

3

Image file formats themselves do not regard the gamma but store pixel values unmodified as the authoring program (e.g. Photoshop) decides to store the values, so RGB and alpha channels have no distinction from image file format point of view (barring potential lossy compression strategies, but that's another topic). However, when you author images in ...

2

You can get fancy with individual weighting on the blur maps if you want to adjust the look, but an equally weighted mix (and yes, it should be additive) will work too. I’m not sure about whether you need to gamma-correct the blurred image before adding it to the source one, but you should definitely get it into linear space before doing the blur; this ...

2

According to Wikipedia (insert standard disclaimer RE accuracy): JPEG does not define which color encoding is to be used for images. JFIF defines the color model to be used: either Y for greyscale, or YCbCr as defined by CCIR 601. YCbCr is a non-linear format. As I mentioned earlier, "Video Demystified" states: "YCbCr is the color space originally ...

2

Almost all image formats store colors gamma-encoded, so if you write out those values to a file then that's what you'll see on opening it. The pixel pickers etc operate on the same values stored in the file. It's much less common to store linear-light color values in a file (one example is digital camera RAW files). When you "see color C1" on the screen, ...

2

the colors are distorted and much brighter corresponding to (186,186,186) color value. If I don't apply gamma encoding then the image file displays the expected color that is (127,127,127). No, the gamma-correct color is not distorted; your expectations are. If your lighting, meshes, textures, and other scene elements were not built to be properly linear ...

1

Welcome to the world of 8-bit graphics! Other answers here are excellent, and most of what you need to know is described well on Wikipedia but let me take you on a human-friendly journey of understanding that I wish someone would have taken me on when I was younger. The first realization that you need to make is that a pixel with RGB values 128, 128, 128 ...

1

Gamma correction originated as a way of correcting the output of a CRT to be a better fit for the human visual system. Modern monitors don't need to do it, but, they followed the CRT and there were millions of CRT's that all had gamma correction and most signals already had gamma correction in them. Today we have a chicken and egg problem...but reversed. ...

1

Yes, I think you're right. The values from a typical color picker would be in a gamma encoding or sRGB encoding and would need to be converted to linear to use as reflectance. This is probably just a mistake in the book. (BTW, in case you're not aware, sRGB isn't actually gamma 2.2 but a more complicated transfer function.)

1

Yes and no. The RGB values are most likely gamma compressed. Consider gamma calibration images like the one below. For a well calibrated monitor the gray value should look the same as the pattern of black and white lines. If you load in the image you will likely find RGB values of $186$. $(186/255)^{2.2} \approx 0.5$, which means that a halftone pattern ...

1

A bump map should not be linearised from sRGB, in theory. A diffuse map or photo contains colour data, which must be encoded in a colour space. Colour spaces consist of two things, a colour gamut (what kind of red is red, what kind of green is green, what kind of blue is blue and what kind of white is white) and a transfer functions (how do you allocate the ...

1

We can not answer this question. This is important, and you need to get this info from the artist (or vice versa you need to give this info to the artist before he begins) It entirely depends on what kind of assumptions were made when the artist was working with the image. Was the artist working by numbers Was the artist working by eye Was the artist ...

1

This is a hard problem since the systems do not in fact tell you how it should operate. The problem is that there are several ways to address this issue: Apply a LUT to all output Let the system color manage Let each application color manage Nearly all of our color management systems are borderline braindead. There is really no sane way to ensure that you ...

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