[Openexr-devel] Saving EXR file one channel at time

[Pavel Hradský]

 Hi!

I need to save an EXR file with several channels (for example 
RGBA+Depth+AmbientOcclusion) in a kind of strange way. I'd like to save 
the RGBA channels first and then, after some time, add a Depth channel 
and then the other channel (layer, whatever) into the same file. I tried 
this by first setting the header to have all necessary channel (names) 
and then filling a framebuffer first with RGBA channels only, writing 
pixels, then creating another framebuffer with depth channel (and same 
header), writing pixels and so on. This is obviously not the right 
approach, since I ended up with a file containing only the last channel 
:-) (I first tried R, then GBA for example).

The reason for wanting to create the single file in several passes is 
memory constraints (the images will be rather big, generated in Direct3D 
and I don't want to hold all of them in memory at once). Is it even 
possible?

I'm using Imf::OutputFile (scan-lines).

Many thanks! (my first post, hopefully correctly sent)

--
Pavel Hradsky
Faculty of Electrical Engineering, Czech Technical University in Prague