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Michael Perez

How To Up Gamma TUTORIAL Minecraft __FULL__

As soon as we compute the final pixel colors of the scene we will have to display them on a monitor. In the old days of digital imaging most monitors were cathode-ray tube (CRT) monitors. These monitors had the physical property that twice the input voltage did not result in twice the amount of brightness. Doubling the input voltage resulted in a brightness equal to an exponential relationship of roughly 2.2 known as the gamma of a monitor. This happens to (coincidently) also closely match how human beings measure brightness as brightness is also displayed with a similar (inverse) power relationship. To better understand what this all means take a look at the following image:

How to up gamma TUTORIAL Minecraft

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The idea of gamma correction is to apply the inverse of the monitor's gamma to the final output color before displaying to the monitor. Looking back at the gamma curve graph earlier this chapter we see another dashed line that is the inverse of the monitor's gamma curve. We multiply each of the linear output colors by this inverse gamma curve (making them brighter) and as soon as the colors are displayed on the monitor, the monitor's gamma curve is applied and the resulting colors become linear. We effectively brighten the intermediate colors so that as soon as the monitor darkens them, it balances all out.

Let's give another example. Say we again have the dark-red color \((0.5, 0.0, 0.0)\). Before displaying this color to the monitor we first apply the gamma correction curve to the color value. Linear colors displayed by a monitor are roughly scaled to a power of \(2.2\) so the inverse requires scaling the colors by a power of \(1/2.2\). The gamma-corrected dark-red color thus becomes \((0.5, 0.0, 0.0)^1/2.2 = (0.5, 0.0, 0.0)^0.45 = (0.73, 0.0, 0.0)\). The corrected colors are then fed to the monitor and as a result the color is displayed as \((0.73, 0.0, 0.0)^2.2 = (0.5, 0.0, 0.0)\). You can see that by using gamma-correction, the monitor now finally displays the colors as we linearly set them in the application.

The first option is probably the easiest, but also gives you less control. By enabling GL_FRAMEBUFFER_SRGB you tell OpenGL that each subsequent drawing command should first gamma correct colors (from the sRGB color space) before storing them in color buffer(s). The sRGB is a color space that roughly corresponds to a gamma of 2.2 and a standard for most devices. After enabling GL_FRAMEBUFFER_SRGB, OpenGL automatically performs gamma correction after each fragment shader run to all subsequent framebuffers, including the default framebuffer.

From now on your rendered images will be gamma corrected and as this is done by the hardware it is completely free. Something you should keep in mind with this approach (and the other approach) is that gamma correction (also) transforms the colors from linear space to non-linear space so it is very important you only do gamma correction at the last and final step. If you gamma-correct your colors before the final output, all subsequent operations on those colors will operate on incorrect values. For instance, if you use multiple framebuffers you probably want intermediate results passed in between framebuffers to remain in linear-space and only have the last framebuffer apply gamma correction before being sent to the monitor.

The second approach requires a bit more work, but also gives us complete control over the gamma operations. We apply gamma correction at the end of each relevant fragment shader run so the final colors end up gamma corrected before being sent out to the monitor:

An issue with this approach is that in order to be consistent you have to apply gamma correction to each fragment shader that contributes to the final output. If you have a dozen fragment shaders for multiple objects, you have to add the gamma correction code to each of these shaders. An easier solution would be to introduce a post-processing stage in your render loop and apply gamma correction on the post-processed quad as a final step which you'd only have to do once.

Because monitors display colors with gamma applied, whenever you draw, edit, or paint a picture on your computer you are picking colors based on what you see on the monitor. This effectively means all the pictures you create or edit are not in linear space, but in sRGB space e.g. doubling a dark-red color on your screen based on perceived brightness, does not equal double the red component.

As a result, when texture artists create art by eye, all the textures' values are in sRGB space so if we use those textures as they are in our rendering application we have to take this into account. Before we knew about gamma correction this wasn't really an issue, because the textures looked good in sRGB space which is the same space we worked in; the textures were displayed exactly as they are which was fine. However, now that we're displaying everything in linear space, the texture colors will be off as the following image shows:

The texture image is way too bright and this happens because it is actually gamma corrected twice! Think about it, when we create an image based on what we see on the monitor, we effectively gamma correct the color values of an image so that it looks right on the monitor. Because we then again gamma correct in the renderer, the image ends up way too bright.

Something else that's different with gamma correction is lighting attenuation. In the real physical world, lighting attenuates closely inversely proportional to the squared distance from a light source. In normal English it simply means that the light strength is reduced over the distance to the light source squared, like below:

The linear equivalent gives more plausible results compared to its quadratic variant without gamma correction, but when we enable gamma correction the linear attenuation looks too weak and the physically correct quadratic attenuation suddenly gives the better results. The image below shows the differences:

The cause of this difference is that light attenuation functions change brightness, and as we weren't visualizing our scene in linear space we chose the attenuation functions that looked best on our monitor, but weren't physically correct. Think of the squared attenuation function: if we were to use this function without gamma correction, the attenuation function effectively becomes: \((1.0 / distance^2)^2.2\) when displayed on a monitor. This creates a much larger attenuation from what we originally anticipated. This also explains why the linear equivalent makes much more sense without gamma correction as this effectively becomes \((1.0 / distance)^2.2 = 1.0 / distance^2.2\) which resembles its physical equivalent a lot more.

You can find the source code of this simple demo scene here. By pressing the spacebar we switch between a gamma corrected and un-corrected scene with both scenes using their texture and attenuation equivalents. It's not the most impressive demo, but it does show how to actually apply all techniques.

To summarize, gamma correction allows us to do all our shader/lighting calculations in linear space. Because linear space makes sense in the physical world, most physical equations now actually give good results (like real light attenuation). The more advanced your lighting becomes, the easier it is to get good looking (and realistic) results with gamma correction. That is also why it's advised to only really tweak your lighting parameters as soon as you have gamma correction in place.

The Unity Editor offers both linear and gamma workflows. The linear workflow has a color space crossover where TexturesAn image used when rendering a GameObject, Sprite, or UI element. Textures are often applied to the surface of a mesh to give it visual detail. More infoSee in Glossary that were authored in gamma color space can be correctly and precisely rendered in linear color space. See documentation on Linear rendering overview for more information about gamma and linear color space.

Textures tend to be saved in gamma color space, while Shaders expect linear color space. As such, when Textures are sampled in Shaders, the gamma-based values lead to inaccurate results. To overcome this, you can set Unity to use an RGB sampler to cross over from gamma to linear sampling. This ensures a linear workflow with all inputs and outputs of a ShaderA program that runs on the GPU. More infoSee in Glossary in the correct color space, resulting in a correct outcome.

To specify a gamma or linear workflow, go to Edit > Project SettingsA broad collection of settings which allow you to configure how Physics, Audio, Networking, Graphics, Input and many other areas of your project behave. More infoSee in Glossary, then select the Player category, navigate to the Other Settings, open the Rendering section, and change the Color Space to Linear or Gamma, depending on your preference.

Texture Import Settings might show textures as being in linear format, because this avoids shaders recognising the textures as being in gamma color space and automatically removing the gamma correction.

You can work in linear color space if your Textures were created in linear or gamma color space. Gamma color space Texture inputs to the linear color space Shader program are supplied to the Shader with gamma correction removed from them.

For colors, this conversion is applied implicitly, because the Unity Editor already converts the values to floating point before passing them to the GPU as constants. When sampling Textures, the GPU automatically removes the gamma correction, converting the result to linear space.

These inputs are then passed to the Shader, with lighting calculations taking place in linear space as they normally do. When writing the resulting value to a framebuffer, it is either gamma-corrected straight away or left in linear space for later gamma correction - this depends on the current rendering configuration. For example, in high dynamic range (HDR), rendering results are left in linear space and gamma corrected later.


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