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Old May 15th, 2009, 02:15 PM   #1
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How do I gamma correct for H.264 "wash out"?

Hi everyone, I read through many forums, blogs, etc, from around the web and can't find a singular fix for the Mac gamma shift that occurs with the H.264 codec rendered movies. The problem I refer to is the washed out or brightening of the file that doesn't match your FCP canvas image.

I have tried several fixes suggested online;

- The "QT Pro - blend-transparency-straight alpha" option.
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- The x264 codec option.
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- The "tiff trick" option.
START QUOTE.
"by Andrew Stewart January 11th, 2009 @ 11:58 pm

Hi all,

I have a quicktime gamma workaround that works for exporting h264s and other codecs that have the gamma shift issue. We use it at work for sending h264’s of telecine color grading reference to some very fussy clients, and so far no complaints :)

The blend/transparency/alpha trick comes close, but the blacks are still a little bit grey and dosent give the same results on both mac and pc. The trick we use has been coined the ‘tiff trick’ and works by tricking quicktime into using default tiff image gamma before an export.

How to do it:

1) Create a small (32×32 pixels or so) tiff or bitmap - dosent matter what color, just make it 8bit and RGB
2) Open a new player and ‘Open image sequence’ and select the tiff/bitmap. set the frame rate to whatever you’re going to be working in
3) Open your desired quicktime in another player, ’select-all’ and ‘copy’ the clip
4) Back in you ‘tiff/bitmap’ movie hit ‘add to movie’ - this will add the video over the top of the tiff/bitmap on a second video layer
5) Export using your desired codec

All going well the gamma will match your original video very closely"
END QUOTE.


So, I've tried all of these options and none seem to do the job. Someone else mentioned doing a gamma 1.1 or higher shift in Compressor and I would like to know how to do this? I can't see any options for gamma adjustments in my Compressor display. Normally I export from FCP using QT conversion and the H.264 codec. That's where the .mov's look washed out. I tried importing one of those .mov's into Compressor but as I mentioned, I can't see any gamma options.

Can anyone offer any guidance or perhaps other options for fixing the H.264 gamma shift?
Thank you.

p.s. Running FCS 2 on Leopard (non-Intel MBP)
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Old May 15th, 2009, 03:42 PM   #2
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The Gamma adjustment in Compressor is under the Filters tab. (lot of good stuff in there that I used to just ignore)

Sorry, I have no experience with the Gamma adjustment. It should be pretty easy to do some tests though.
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Old May 15th, 2009, 03:45 PM   #3
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Quote:
Originally Posted by Chad Hucal View Post
Someone else mentioned doing a gamma 1.1 or higher shift in Compressor and I would like to know how to do this?
In Compressor, go the the Inspector and click on the icon for "Filters".

Click the "Video" tab and scroll down to the filter called "Gamma Correction" and click it (a check mark will then appear).

At the bottom of the Inspector will be a slider, or you can simply enter a figure in the box (which has a default of 1.00).

Try entering 1.1 for a start and then output and compare to your original in FCP. Keep adjusting the Gamma Correction amount until you feel the output is a good match to your original.
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Old May 15th, 2009, 03:55 PM   #4
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Quote:
Originally Posted by David Knaggs View Post
In Compressor, go the the Inspector and click on the icon for "Filters".

Click the "Video" tab and scroll down to the filter called "Gamma Correction" and click it (a check mark will then appear).

At the bottom of the Inspector will be a slider, or you can simply enter a figure in the box (which has a default of 1.00).

Try entering 1.1 for a start and then output and compare to your original in FCP. Keep adjusting the Gamma Correction amount until you feel the output is a good match to your original.
Hi David, you're actually the person I was referring to when I mentioned the 1.1 gamma option but it appears we are unable to send other members personal messages on this board. I was going to contact you directly but didn't see how it was possible. So I'm glad you read my post, thank you for replying. I'll try this out in the next 24 hours and post my results.

Still open to more options if they're out there also...
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Old May 16th, 2009, 02:10 PM   #5
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Hmm, quick question. I don't have any tabs along the top visible in Compressor's Inspector window. I've looked through the manual and I can see the tabs in the illustration they use but my Inspector window doesn't show these. I just have the basic tabs for "A/V attributes" and "Additional Information".

Is my Compressor missing some content or is there a way to reveal the filter tabs? I can't find anything in any of the drop down menus.
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Old May 16th, 2009, 02:28 PM   #6
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Sorry, never mind, I found the tabs. Trying it now.
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Old May 16th, 2009, 05:50 PM   #7
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Thanks David! That gamma correction worked perfect, looks the way it should now. 1.1 was enough to match my original FCP canvas image.

Thanks again for your input. Greatly appreciated.
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Old May 16th, 2009, 10:22 PM   #8
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Hi,
Yes, I use this same method, although I usually go with a 1.2 increase, but to each his own! Another thing I've noticed is that the color reproduction varies greatly when you view a QT movie on a PC, even if you have the latest version of QT running, the thing I find odd is that even though the PC is a native 2.2 gamma, the colors are always lighter/washy when viewed on the PC (even after doing the 1.2 gamma bump in Compressor) I guess that's an issue I simply have no control over...

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