Re: SMTPE DPX

On Thu, 14 Apr 2005, Stefan v. Wachter wrote:

> For testing I have put some smaller sample dpx files on
> http://home.mnet-online.de/svwa/pub/images/
> These are linear dpx files with 10 bit and 16 bit depth, RGB and Grayscale 
> colorspace.

Woo! Woo! GraphicsMagick is able to load all of these files.  I can 
not attest to color correctness though.  All of the images look good 
to me except that rgb10sz307.dpx has a yellowish tinge.  Maybe this is 
normal for an old film?

The most interesting file is sample-10bit.dpx.bz2 since it is planar. 
I assume that it is supposed to load as solid gray?

> By the way - is the GraphicsMagick 1.2 branch already available via CVS?
> I tried this:
>> cvs update -r GraphicsMagick-1_2 ChangeLog
> and got:
>> cvs update: warning: cannot open /GraphicsMagick/CVSROOT/val-tags 
> read/write: Permission denied
>> cvs [update aborted]: no such tag GraphicsMagick-1_2

There is no GraphicsMagick-1_2 branch tag.  We establish the branch 
shortly before the first release on that branch.  The code in that 
branch is essentially under "maintenance" from that point on.

The code is all on CVS head.

You can use

   cvs update -A ChangeLog

to obtain ChangeLog on the default (head) branch, or could even use

   cvs update -r HEAD ChangeLog

but then the sticky tag would be set on the file.

I have yet to encounter a DPX file which is clearly log encoded.  Do 
these files really exist?  What are the obvious signs when a log 
encoded file is mistakenly viewed as linear?

Bob

> Bob Friesenhahn wrote:
>
>> I have continued to make good progress with DPX support.  DPX is the only 
>> supported format I am aware of which supports 10 or 12 bits per sample as 
>> part of its standard definition.  Unlike TIFF, GraphicsMagick can support 
>> DPX without an add-on library.  As a result, I have included a few DPX 
>> files as test input "deep" images.
>> 
>> DPX can optionally support log encoding over a 2.048 density range, which 
>> is sufficient to capture the full range of film negatives. Film negatives 
>> have approximately linear gain when plotted on a 2.048 density log scale. 
>> This can be seen as a form of HDR with minimal resolution loss for film 
>> content.  By using a colorspace to postpone the conversion to linear sRGB, 
>> the original data is available at the C API level.  This will allow us to 
>> support lossless conversion to some other HDR format in the future.  For 
>> example, when we add EXR support, then we would be able to convert a log 
>> DPX image into EXR format without losing any dynamic range.
>> 
>> Bob
>> ======================================
>> Bob Friesenhahn
>> [email protected], http://www.simplesystems.org/users/bfriesen/
>> GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
>> 
>> 
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>
>
>
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======================================
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/


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