The heart of the problem of dark renders is in that the image and monitor gamma values are different.

Gamma is the degree of nonlinearity of the color gradient from dark to bright values. In mathematical point of view the linear gamma value is 1.0 and this is why software such as Max, V-Ray by default performs calculations in the gamma 1.0. But the gamma 1.0 value is consistent only with the «perfect» monitor, which has a linear dependence of the display from white to black. Because there is no such monitors, the actual gamma of devices is nonlinear.

The gamma value for the video standard NTSC is 2.2. For computer displays the gamma value is typically between 1.5 and 2.0. But for convenience the nonlinearity of the color gradient on all screens is considered as 2.2.

When the monitor with gamma 2.2 shows an image with a gamma 1.0 we get dark gamma 1.0 colors instead of needed gamma 2.2 bright ones. So the middle-range colors (Zone 2) become dark when viewing the gamma 1.0 image with the gamma 2.2 output device. However, in range of dark tones (Zone 1), gamma 1.0 and 2.2 representation is quite similar, what lets to display the shadows and black colors properly.

In the areas of light tones (Zone 3) there also are the great similarities. Therefore, bright gamma 1.0 image is also quite correctly displayed on the gamma 2.2 monitor.

And so, in order to get at the appropriate output in Gamma 2.2 the source image gamma should be modified. Surely this can be done in Photoshop, simply by adjusting gamma there. But each time to change the image settings, saving them to your hard disk, and editing in raster editor can hardly be called convenient. Because of that we will not consider this option, and in addition this method provides an even more significant deficiencies. Modern renderers, such as V-Ray, calculate the image adaptively, so the calculation accuracy depends on many parameters, including the light brightness in the area. Therefore, in the shadow areas image is calculated less accurately and become noisy. And in the bright and visible areas the calculation passes with more accuracy and with minimal artifacts. This allows faster renders due to the saving time on a slightly visible areas. By raising the output image gamma in Photoshop you change the brightness of those parts, which renderer considered as a less significant and reduced the quality of a calculation. Thus, all unwanted artifacts become prominent, and the picture will look awful, but more bright than before :) In addition the gamma of textures also will change and they will look pale and discolored.

The only correct way out of this situation is the changing the gamma value in which the renderer is working. That way you will get an acceptable brightness in the midtones and there will no obvious artifacts, as when changing gamma in raster editor.

We will show you how this is done in V-Ray renderer and 3ds Max.