EXR slow to render?

[Kerro Perro]

This may be a really stupid noob question but why is the .exr format so much slower to render than say a .tiff? (both at full float..)

I want to use them simply because i'm using render channels and the exr's don't have those annoying black lines around the alpha but when it's this much slower it's not really worth it...

EDIT: whoops i just figured out how to get rid of the black lines (straight vs premultiplied alpha ) so no need for exr for that but still curious as to why they render so slow..

[SamHowell]

The file format you save your rendered frames as shouldn't make any difference to your actaul render times at all.

Maybe the time taken to process those frames before actaully saving them as the larger .exr has some kind of effect? This should be negligible anyway.

Please correct me somebody if I'm wrong.

[ActionArt]

It should make very little difference. Now I'm curious, I'll have to test...

[Kerro Perro]

That would be cool - i noticed it several times with the same scene, only thing of note was that it had a lot of seperate framebuffers, maybe that was it? Anyhoo i can't check again right now so would be cool if someone else can confirm or deny this ;)

[grahamef]

My first guess would be that it's not related to the actual rendering time, but that the disk I/O is a bottleneck with the larger files.

[Kerro Perro]

Hey guys i haven't had a chance to check this again yet but i just spoke to Rob Wuijster (Rork) and he said it must've been the many custom framebuffers i was using: writing out to them costs a lot of time.

He's pretty much the most experienced guy i know so i'm pretty sure he's right ;)

Will test some more as soon as i have the time!