Re: [Openexr-devel] EXR B44A Usage

[Peter Hillman]

Hi Chad,

I'm afraid I only have an unhelpful answer for you: it's best to test and work out what works best for you.

I reckon the five important metrics in picking a compression scheme are:

• Write time
• Read time
  
• File size on disk
• Quality (if using a lossy compression scheme)
• Compatibility with other tools

Compatibility could be an issue for the DreamWorks schemes, DWAA and DWAB, as it was introduced in OpenEXR-2.2.0 and may not be supported in all your tools yet. The other metrics depend on the kind of images you are creating, your software, and your system setup. Compression schemes behave differently depending on the image content and the rendering algorithm. Also, how you choose to trade off time against storage space and image quality is really up to you, so it's hard for anyone else to give a definitive answer.

Given that, I'd suggest running your own tests to decide. You might try all the schemes with exactly the same image sequence and compositing setup, measuring the total time it takes to render the images, the compositing time, and the file size. Beware that timing tends to be quite variable for all sorts of incidental reasons that may not be anything to do with the compression scheme. For lossy compression, you could check the final images look OK to you compared to a lossless compression approach (e.g. ZIP).

Personally I'd avoid lossy compression on images that will be further processed unless there's a clear win elsewhere that's important to you. I'm guessing that "Lossy 16-bit float, in blocks of 16 scan lines" is the "B44" scheme. "B44A" may well be a better choice than B44, but it would be worth running tests of all options anyway.

Peter

On 29/09/16 03:00, Chad Ashley wrote:

Hello,

This is my first posting to this list, so good morning everyone! I had a question: When should one use the B44A compression? 

I am a 3D artist rendering primarily out of Arnold and I normally use "Lossy 16-bit float, in blocks of 16 scan lines" compression. Should I look to use the B44A compression instead? What are the upsides and downsides (if any)? Or, should I be using a completely different compression?

3D App: C4D

Renderer: Arnold

Compositor: Fusion, After Effects

Thank You,

-chad

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