Introduction


  • This lecture will discuss Linear Workflow, what it means, and how to implement it in V-Ray
  • This lecture-only topic is approximately 10 minutes in length

 


 

Contents



Overview
Available Materials
Lecture                                       


Overview


You will learn about the Linear Workflow theory, what it means, and how to implement it in V-Ray    


Available materials


To set up the lesson follow the links below and download all available materials.

Lesson plan download
Presentation (Lecture) download
Demonstration tutorial download 
Scenes & Assets download

 

Lecture



1. Terminology

How the computer creates images and how we see them are not always in the same setup. Here’s some terms to be aware of when thinking about Linear Workflow:

a) Linear Workflow

  • A method of working in rendering where the light and color calculations from texture image input to render output are accurate and take into account gamma corrections

b) Gamma

  • A value that controls the luminance, or brightness, of an image

c) Color Space

  • A way to reproduce accurate colors digitally on physical displays that organizes the colors that are to be reproduced by the system

d) sRGB

  • The color space for most monitors and computer displays; this is the color space we are exposed to the most

e) Image Bit Depth

  • The color information for an image is stored in numerical values under RGB channels. Bit depth defines how much color value an image file can hold
  • 8 bit – most “normal” images we view are in 8 bit
  • 16bit and 32bit float images allow for a much wider range of color values, though file sizes are larger

 

2. Viewing and Color Space


  • Monitors and displays usually present color information in sRGB color space
  • Depending on what color space in which you view an image, you may get a different look
  • Image on the left is properly corrected to display on an sRGB display, while the same image is shown with no color correction as it was rendered directly in Linear Workflow
    • Improper viewing may lead to the artist assuming their scene is not lit properly

 

 

Gamma = 2.2

Gamma = 1.0

 


 



 

 

3. Linear Workflow Viewing in VFB


Linear Workflow requires:
a) making sure to properly view renders with a gamma correction of 2.2
  • Renders are corrected to view in sRGB automatically in the VFB by default
  • You can toggle sRGB On and Off easily
  • Saving an 8 bit image out to a file from the VFB will respect the sRGB toggle and save the image as seen in the VFB

 

 


b) any texture images imported into the scene be properly gamma corrected
  • Texture files are “reverse gamma corrected” to linearize them to calculate properly in the render
  • Gamma value of  2.2 (specifies the original gamma baked into the image)
  • All 8bit and 16bit color images to be used as textures on color attributes will need to have Texture Input Gamma attribute added to them
  • Bump and Normal maps and other grayscale images do not need the Texture Input Gamma node
  • When both the input images and the output renders are gamma corrected properly, the image view will be accurate

 

 

 


c) Linear Workflow Method 1

  • Simply check on the Linear Workflow checkbox in the Render Settings under the VRay tab
    • This is the fastest and easiest way
  • Automatically gamma corrects incoming File texture nodes
  • This method may not be 100% accurate in all situations
    • Some images may not receive proper gamma correction when they are mapped to reflections, the color of a light, or the color of a light material
    • Some texture images that are already linear (like EXR files) will receive gamma correction without needing it
  • You still need to view renders with sRGB correction (gamma 2.2) Enabled in the VFB or in compositing

 

 

 


d) Linear Workflow Method 2

  • Leave the Linear Workflow checkbox turned Off in the Render Settings
  • Manually apply gamma correction to each incoming file texture node
    • Most images are sRGB and need to be linearized
    • Some images such as EXR files are already linear and do not need to be gamma corrected to be used as textures
  • You still need to view your renders with sRGB correction

 

 

 


e) Linear Workflow and Texture Images

  • The render on the left is missing the Texture Input Gamma attribute on the guitar’s color texture map and the guitar is incorrect and looks washed out
  • The render on the right has the Texture Input Gamma attribute applied on the guitar’s color texture map and the guitar is correct
  • Textures that are not gamma corrected will appear light and washed out

 

Guitar Diffuse Color Texture File Node



 



 


f) Linear Workflow in Compositing

  • Images rendered through Maya Batch Render need to be gamma corrected in compositing
    • For example, this is done automatically in Adobe After Effects CC when rendering 32bit EXR files, as shown below
    • 16bit and 8bit image renders will need an extra step to gamma correct them in composite, as shown on the right, which uses the Exposure Effect using a Gamma value of 2.2
  • Renders not gamma corrected will look dark and contrasty

 

32bit EXR render



 

8bit JPG render



Conclusion



a) Color Space

  • Linear on an sRGB display

b) Quick way to enable Linear Workflow

  • Automatically gamma corrects all file texture nodes
  • May not be accurate for all situations

c) Preferred method for Linear Workflow

  • Manually gamma correct incoming color texture file nodes

d) Always need to view renders in sRGB mode in VFB

e) Always need to gamma correct renders in compositing

  • Gamma of 2.2
  • Render 16bit or 32bit files for best color correction range