The compression attribute will be in a different place within the header
depending on the number of channels in the file (due to the layout of the
EXR header).
Adrian's snippet is simply finding the 'compression' attribute name within
the header, since that is one of the standard EXR attributes. From there,
based on known information about the EXR file layout, he can determine where
the actual compression attribute value is stored.
The read size of 1024 is pretty much an arbitrary value; you may need to
read a larger chunk in order to get far enough into the file to locate the
compression attribute if your file has a lot of channels. If you know the
names of all the channels within the file, you could figure out exactly how
many bytes to read, or even start your read from a predefined offset to keep
your data buffer as small as possible; otherwise, you'll just need to make a
safe estimate.
Check out this doc for a nice simple example of the structure of an EXR
file: http://www.openexr.com/openexrfilelayout.pdf
Hope this helps.
-Nathan
-----Original Message-----
From: Dan Rosen
Sent: Tuesday, May 22, 2012 9:59 AM
To: Nuke user discussion
Subject: Re: [Nuke-users] How to check zip compression type for EXR
images...?
This is great! Can you let us know what index number the datatype is
in? I'm finding it hard to tell.
thx
Dan
On Mon, May 21, 2012 at 7:30 PM, Richard Bobo <[email protected]> wrote:
Adrian,
Brilliant - I'll be making it into a nice little pulldown menu utility
function! And, looking a bit deeper at your code, of course, so I can
learn
some more Python... 8^)
Thanks!
Rich
Rich Bobo
Senior VFX Compositor
Mobile: (248) 840-2665
Web: http://richbobo.com/
"Man has been endowed with reason, with the power to create, so that he
can
add to what he's been given."
- Anton Chekhov
On May 21, 2012, at 6:40 PM, Adrian Baltowski wrote:
Hi
With just few lines of code and totally simplified
**********************************
compList = ['None', 'RLE', 'ZIP', 'ZIP 16 lines', 'PIZ', 'PXR24', 'B44',
'B44A']
n = nuke.selectedNode()
file = nuke.filename(n, nuke.REPLACE)
fd = open(file, 'rb')
header = fd.read(1024)
index = header.find('compression')
comp =ord(header[(index+28):(index+29)])
print compList[comp]
***********************************
Each exr file MUST have compression info in the header and this info is
placed just after channels info. It's simple to get actual size of
channels
list but I quickly set 1024 bytes of a headroom.
Best
Adrian
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