Posted: Jun 13, 2011
Published by: the area
Homepage: Visit the page
Software: Autodesk 3ds Max
Many of you will have heard the terms “linear workflow” and “gamma correction”. It is a must for 3d rendering, especially interior visualisation because it fixes so many problems with render samples, light falloff and cuts post processing tasks in half. I am not going to go into depth about linear workflow and gamma correction as it can become a complex subject but to put it simply, this workflow will increase the fall off of your lights so that light travels further throughout your scene.
By default, both Autodesk 3ds Max and Vray work in gamma 1.0 (linear space). In Autodesk 3ds Max preferences under enable gamma/lut correction, change the gamma to 2.2. Autodesk 3ds Max will now have an input gamma of 1.0 and an output gamma of 2.2 for standard viewing.
In Vray colour mapping, set it to linear multiply and set gamma to 2.2. It is recommended to work in pure linear space and complete your gamma correcting in post production. Tick don’t affect colours (adaptation only). This will render out a darker version of your image. To see the actual result in gamma 2.2 space, click the sRGB button in the Vray frame buffer during or after rendering.
Do not tick linear workflow, it may seem like a magical linear workflow button but it is not. Instead it is a quick and brutal way of correcting Vray materials to match a linear workflow and the result can be less than desired.
When adding a texture map to the material editor, in the bitmap loader, manually change the gamma to 2.2. Although they work in gamma 1.0 (linear space), digital cameras apply a total curve which adjusts the gamma to 2.2 to make the image appear more pleasing to the eye. Unless you have advanced photography skills and you are working with RAW images, this is a helpful process for the average happy snapper. It means that, as you may have guessed, the texture map JPEG you took with your digital camera is already at gamma 2.2.
When working with linear images and gamma 2.2, the output is mathematically correct as opposed to just looking correct. In post processing, any adjustments will give predictable results and are much easier to manage. Linear images result in a much larger tonal range. To compensate, it is best to save out as a TIF file which is at least 16 bit colour. Saving out an 8bit file format may result in some colour banding because there is not enough tonal range. Never render out JPEGs because this file format is not designed for linear images and you will lose a lot of data when saving in this format initially.
This tutorial is written by James Cutler who is a creative consultant and founder of MintViz. MintViz is a creative consultancy that provides tutorials, tips and resources for the CG industry.
Newest users comments View All 4 Comments