I just checked and playing the video in iTunes also looks correct.
Strange that iTunes doesn't take advantage of Core Video like Safari
seems to.
On Apr 8, 2006, at 12:39 AM, M. Robert Spryn wrote:
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.)
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.
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.
------------
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.
------------
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?
------------
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?)
-----------
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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