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Core Video/ H.264 Color issues

Hello all,

I've been searching high and low to find the solution to this problem, and baffled at how few people seem to be talking about it.

As far as I can tell, any computer which supports Core Video is displaying many of apple's codecs with incorrect color, including the famous h.264 codec. The problem also appears to extend to some PC's (I believe Direct Draw Acceleration utilizes the video card to play back quicktime files on some machines.)

You can read about my initial assessment and examples of the problem. http://sprynthesis.com/blog/?page_id=51


In this e-mail I'll link to further testing I performed over the past 24 hours that clearly identifies my problem.

To follow along with my e-mail, you can download the sample files. http://sprynthesis.com/qtplayer_issue.zip

First here is my workflow.

I am working in Maya (3D app for those who didn't know) and generating tiff sequences. Those tiff sequences are then put together in a compositing app like Shake or After Effects (I have tested both thoroughly.) I then render those tiff sequences out into a self contained quicktime movie using the (totally lossy) animation codec. No problems through this point. Then I compress the file (either straight through quicktime or using the Compressor application) into an h.264 file. This file then plays back with incorrect colors on my machine, and any other machine that supports core video, but looks fine on those that don't. The colors aren't totally wacky, but they are faded and shifted slightly.

This has been brought up in apple forums, and on macintouch and macfixit.

http://discussions.apple.com/thread.jspa? threadID=210793&start=0&tstart=0
http://www.macintouch.com/readerreports/quicktime7/topic2894.html
http://www.macfixit.com/article.php?story=20060331083618226&query=h.264

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So after reading my web page about this and downloading the sample files, you can test this for yourself here by breaking out the DigitalColor Meter application from your utilities folder (set the pop-up menu to "RGB As Actual Value 8-bit).

1. Inside my folder of sample files, open the first movie called "1.single_tiff.mov". This is simply one of the tiff files saved as a self contained movie in quicktime.
Mousing over the squares (http://www.sprynthesis.com/qt_issue/ likethis.jpg) will give you your base values which all the other files SHOULD match somewhat closely. Use this as a reference file to compare all the other quicktime files to.


The bottom row should be various levels of greys, the next row up should only contain blue values, and so on with the red and green rows. The rows above that are various combinations of RGB values just for further testing.

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2. Now move on to the "2.ae_animation.mov" file. This is the tiff sequence compressed out of after effects using the animation codec. The values of these squares should be identical to that of the first file, and they are.

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3. Now look at the "3.h.264.mov" file. The results you will get for the RGB values of these squares will depend on whether or not your computer supports core video. If it doesn't support core video (like the PowerPC mac mini) then your RGB values will be extremely close to that of the source file. (Hooray! The problem doesn't affect you.)

If your computer does support Core Video, then you will see that all the black levels - except for the pure black and white (its a gamma curve problem?) - are brighter than they should be. When you mouse over the squares that should be solid RGB values, you see anywhere from trace amounts to extreme levels of other colors showing up. This is quite a problem! What's worse? Calibrate your monitor instead to a gamma of 2.2 (like most pc users and a lot of pro mac users do) and the color shift is much worse.

Now is the fun part. Open that same h.264 file with Firefox, or download an application like the "Nice Player" (and disable core video in the Nice Player prefs.) The color problems dissappear and the file looks like its supposed to (like those without core video, the rgb values don't match exactly, but at most they are off by a hair... very acceptable)!! Well crap... what's a guy to do? Use Sorenson 3?

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4. Open the "4.mpeg-4.mp4" file. The RGB values should look pretty good in quicktime no matter what computer you view them on. Although when viewed in Nice Player or Firefox the RGB values actually seem a little low on the color squares. (Maybe this is because no ICC profile is embedded in mp4 files?)

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So you should be able to see my problem pretty clearly as long as your computer supports core video. My question is what is the solution? Whoever encodes the Apple HD trailers seems to know. Those videos look great on computers with and without core video.

Anyway, that's my 2ยข. I am determined to understand what's going on with my color conversions. Anyone who has any ideas for a solution, drop me a line! I really want to be able to trustfully use h.264 instead of falling back to Sorenson 3.

Thanks,
Robert Spryn

(Oh btw file "5.uncompressed.mov" is there to show how the uncompressed codec seems to clamp the RGB values.. something it doesn't seem like the "uncompressed" codec should do. Is this to make it safer for tv broadcast maybe?) _______________________________________________
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