Re: [Openexr-devel] PIZ-Compression / Multithreading

[Brendan Bolles]

On Nov 24, 2009, at 2:56 AM, David wrote:

> i've got two little questions:
> I'm developping a c++-tool to convert OpenExr-images from Maya to  
> OpenExr-images which are optimized for Nuke (the tool creates a  
> data window and converts the images into scanline-mode with piz  
> compression).


Hey David, I think you'll find that to optimize for Nuke, you'll also  
want to switch to Zip compression.  The main reason is that Nuke's  
scanline renderer can go through and read just the lines it needs.   
Piz and Zip16 lump 16 lines together (right?), so Nuke has to read  
the whole chunk.

Also, since you'll tend to read the files many times more than you  
write them, Zip will decompress faster than Piz and you'll get a  
little speed bump on every read.

Finally, to take advantage of multithreading, you have to call  
writePixels() with a lot of scan lines.  For writing, I usually just  
do one big writePixels() call with all the lines together, but I find  
doing 128-line chunks is almost as fast.


Brendan