February 21, 2008

Quicktime Gamma Stripper

Besides the usual gamma differences and Windows graphics acceleration, gamma tags in QuickTime files can change appearance of files across platforms.

Frantic Films Software explains: "Quicktime has a feature, mostly hidden from users, which is designed to adjust the display gamma of quicktime movies on different machines to compensate for display difference. Deep within the file, there is sometimes a little tag called 'gama' lurking which tells the Quicktime player what gamma correction the file was encoded with. While this is well-intentioned, motivated by the difference in display gamma between PCs and Macs, the Quicktime player offers no way to view this tag and change it.

To work around this issue, we have created a small tool that strips the 'gama' tag out of offending quicktimes. It's a very simple tool which operates on all the file names and folders given to it."

There's more info as well as the
QuicktimeGammaStripper utility at Frantic Films Software. It's for Windows but there appears to be instructions for Mac too.

Adobe has a technote for strictly After Effects-related issues: QuickTime movies exported from After Effects CS3 are darker or lighter than expected.

Update: this utility appears to be missing from Frantic; I'll look around for it.

Update 2: File found on internet; see QuicktimeGammaStripper utility for Windows.

Update 3: Some websites directly copy postings (cf. here & Windows Live) and/or hide their sources, but at least some of them give something if only to keep viewers from leaving their site. In one case, The DV Show follows but at least posts QTGammaStripper.

Update 4: Check out updates
QTGammaStripper for OS X PPC and Win32 (another gamma stripper app) and Brightness Issues with H.264 QuickTime, a survey and x264 solution by Chris & Trish Meyer.


Gene said...

Hey Rich, I would love to get this utility off of you. I can't find your email address on here so please if you don't mind email me at gene crucean at gmail dooot com

No spaces obviously. Cheers

Rich said...

Hi, I'm at aefilter at yahoo but the machine it was on went offsite for a week, and the data disk with the copy is missing. So it'll have to wait til the machine gets back.

Kyle said...

The simple way to kill this lut being applied to the quicktime is to do a literal text replace of 'gama' in the quicktime to 'kama' or something. It can be achieved with Sed too.

Rich said...

Could you be exact so someone can replicate your steps?

In Windows Vista with Notepad, there was no text gama but there was a Gam as part of hex sequence.