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Date: Fri, 08 Feb 2008 12:44:02 -0800
Subject: Re: [Tiff] 32-bit floating point RGB images (and gamma)
From: Chris Cox <ccox@adobe.com>
To: Edward Lam <edward@sidefx.com>, TIFF <tiff@lists.maptools.org>
Message-ID: <C3D1FF12.675DB%ccox@adobe.com>
Thread-Topic: [Tiff] 32-bit floating point RGB images (and gamma)
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Status: RO

Edward;

Photoshop by default, reads and writes all 32 bit/channel documents as gamma
1.0.  The only way Photoshop would  read it as gamma 2.2 is if you included
an ICC profile in the TIFF file that specified gamma 2.2 (and then Photoshop
would complain because we really want floating point data as gamma 1.0).

Now, Photoshop DOES correct for the display -- your gamma 1.0 image will
look correct on the display because Photoshop converts the data to the
display gamma (and chromaticities) when displaying the image.

You might want to read up on color management.

Chris



On 2/7/08 7:27 AM, "Edward Lam" <edward@sidefx.com> wrote:

> Hi Folks,
> 
> What's the best way to express a TIFF file that has 32-bit floating
> point, *linear* RGB data? If I do the dumb thing, then Photoshop CS3
> Extended interprets the data with a 2.2 gamma. However, ImageMagick
> seems to display the image without the gamma correction.
> 
> Looking at the TIFF 6 spec, the default TransferFunction seems to be 2.2
> gamma correction if unspecified for RGB PhotometricInterpretation?
> However, one can't easily provide a linear TransferFunction for 32 bits
> per sample data.
> 
> Thanks,
> -Edward
> _______________________________________________
> Tiff mailing list: Tiff@lists.maptools.org
> http://lists.maptools.org/mailman/listinfo/tiff
> http://www.remotesensing.org/libtiff/

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