Re: DPX Support

On Thu, 7 Apr 2005, Robin Rowe wrote:
>
>> Right.  Supporting log format should as simple as inserting translation 
>> tables based on the Kodak documentation.
>
> You may want to look at how CinePaint handles it. We cheat, use a bit shift 
> instead of a gamma-correct table lookup. Bit-shift is very fast and doesn't 
> have round-trip rounding errors.

Speaking of performance, I found the DPX specification to be complex 
enough that I ended up not worrying about performance and focused on 
functionality instead.  Interestingly, I find that performance on 
Intel Xeon (running FreeBSD) is reasonably good, but there is a 
performance issue on UltraSPARC.

GraphicsMagick has what I call "read/write" tests where the read/write 
process is:

  reference --write--> version 1 --read/write--> version 2 --read

The final image is then compared (mean distance method) with the first 
image written ("version 1").  This is intended to verify that writing 
and reading the image does not corrupt it.  It is not intended to be a 
performance benchmark.

Under UltraSPARC/Solaris I am seeing performance problems when 
writing, so with a 2K frame this test is taking 2.620 seconds on Intel 
Xeon but it takes 6.732 seconds on UltraSPARC.

There is also a "blob" version of the tests were all images are 
resident in memory.  In this case Intel Xeon takes 2.261 seconds and 
UltraSPARC takes 5.450 seconds.

In both cases, time reports that most time consumed is user time.

Normally timings are not much different between these two machines. 
Investigation will likely find that there is some stupidity somewhere 
rather than that the code really does optimize that much better for 
Intel than it does for SPARC.

Here are the current 10-bit packed DPX read and write rates (in 
megapixels per second) for SPARC and Intel Xeon:

        Read   Write
SPARC  3.7    1.5
Xeon   11.1   4.1

Bob
======================================
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/


-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now.
http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click