Re: [Openexr-devel] Reading Only Specified Channels

[Florian Kainz]

Jeff Higgins wrote:
> I'm just starting to get into openexr and I have a question about what 
> the current version supports.
>
> If I have an exr image that has say 12 channels and I only need to read 
> 3 of them (not necessarily RGB) does the reader support only reading the 
> 3 channels that I'm interested or do I need to read the entire file just 
> to get the 3 channels that I'm interested in.
>
> My inclination is that is very much possible. If so is there example 
> code that I can use as reference.

Yes, this is possible.

Before reading any pixels from the file you
must tell the InputFile object about the
memory layout of your frame buffer using the
setFrameBuffer() method.  If the file contains
channels that are not in the frame buffer, then
those channels are discarded during reading.
If the frame buffer contains channels that are
not in the file, then those channels are filled
with a default value.

For more information about the OpenEXR API see
ReadingAndWritingImageFiles.pdf, available on
the OpenEXR web site.

Florian