Linear Workflow An Introduction Lesson Introduction Orientation This

Linear Workflow: An Introduction

Lesson Introduction – Orientation • This presentation 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

Lecture: 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 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 – Gamma – A value that controls the luminance, or brightness, of an image – Color Space – A way to reproduce accurate colors digitally on physical displays that organizes the colors that are to be reproduced by the system – s. RGB – The color space for most monitors and computer displays; this is the color space we are exposed to the most – 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 – 16 bit and 32 bit float images allow for a much wider range of color values, though file sizes are larger

Lecture: Viewing and Color Space • Monitors and displays usually present color information in s. RGB 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 s. RGB 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

Lecture: 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 s. RGB automatically in the VFB by default • You can toggle s. RGB On and Off easily • Saving an 8 bit image out to a file from the VFB will respect the s. RGB toggle and save the image as seen in the VFB

Lecture: Linear Workflow and Texture Images • Linear Workflow requires: 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 8 bit and 16 bit 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

Lecture: 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 s. RGB correction (gamma 2. 2) Enabled in the VFB or in compositing

Lecture: 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 s. RGB 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 s. RGB correction

Lecture: 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

Lecture: 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 32 bit EXR files, as shown below • 16 bit and 8 bit 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 32 bit EXR render 8 bit JPG render

Lecture Conclusion: Linear Workflow – Color Space – Linear on an s. RGB display – Quick way to enable Linear Workflow – Automatically gamma corrects all file texture nodes – May not be accurate for all situations – Preferred method for Linear Workflow – Manually gamma correct incoming color texture file nodes – Always need to view renders in s. RGB mode in VFB – Always need to gamma correct renders in compositing – Gamma of 2. 2 – Render 16 bit or 32 bit files for best color correction range