Using sRGB (Standard RGB) to Correct Images

Use sRGB can be used to evaluate images loaded into the texture channels in sRGB color space.

There are two aspects to Use sRGB; according to the image file you want to load.

• HDR, EXR for the IBL or any image whose Gamma value is set to 1 in any image editor.
  Activating the Use sRGB box can cause the image to brighten or darken. Therefore, if the loaded image is of this type, please DO NOT activate this feature (it is deactivated by default).

  The Use sRBG is OFF.	The Use sRBG is ON.

• The gamma values of the common Jpeg, Jpg, BMP, PNG, TGA, GIF images are mostly non-linear. Therefore, when the image of this kind is loaded, the Use sRGB box MUST BE Activated (by default). Otherwise, the result will be brighter than it is supposed to be in the real world.

  The Use sRBG is OFF.	The Use sRBG is ON.

Theory of Gamma and Images

Basically, the color space of the real world is defined as Linear one. And the parameter for defining it is Gamma. Therefore, the Gamma Value for the color space of the real world is set to 1. Linear gamma curve illustrated below:

Because of the hardware limitation of the monitor and for optimizing the image files (defined by sRGB), the Gamma values of them are non-linear (2.2 and 0.45).

However, the image displayed on the monitor will finally shows a linear color space because the complemented gamma curves of the image and the monitor.

PBR Color Space and sRGB

In PBR Color Space mode, images for the base color or diffuse are demanded to be linear in order to show the most correct result of PBR. It basically assumes that each image loaded into the Base Color or Diffuse channel is of 1 gamma value.

In order to complement the gamma value of the monitor (2.2), the PBR Color Space increases the gamma value of the loaded image to show the shader result as you see in the real world.

However, if the gamma value of the loaded image file is non-linear, then the PBR result of the texture will be brighter than the true color.