Understanding openEXR image compression methods¶

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This document is now available as handy book on books.rxlab.guide!

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The OpenEXR format may seem a bit complicated at first, and a lot of people still claim that “Quicktime Animation has better compression or performance“, that “nothing equals ProRes“, or that “PNG is easier to use“, for example. This is all wrong. Let’s explain!

• Introduction
• Summary
• Luminance/Chroma option
• Formats you don’t know you already know
• Summary by usage and type of image
• Details
• A note about frame sequences

When using the OpenEXR format, it may be hard to determine what is the best data compression to use, and the question is raised very often. This document is an attempt to answer it, depending on what is your need with the file and what type of image you’re storing.

A compression is said to be the best for a specific need when its read or write speeds better fit the application, and the file size is the smallest available.

Many thanks to Dino Muhić for his expertise about DWA

Types of images¶

In this document, we’re distinguishing between the following different types of images:

• Grainy video or animation
  Photographic images (including realistic CGI) or animation with grain

• Video
  Photographic images (including realistic CGI) without grain

• Animation, Graphics
  Highly stylized images such as 2D Animation, Motion Graphics, stylized 3D Animation, or 3D passes such as Z-Depth, Normal…

• Solid colors, large flat areas
  Images mostly consisting of solid colors, such as alpha or id channels

• Texture maps
  Multi-Resolution files