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Re: [Openexr-devel] Color Space Settings
From: |
Florian Kainz |
Subject: |
Re: [Openexr-devel] Color Space Settings |
Date: |
Mon, 22 Mar 2010 10:56:41 -0700 |
User-agent: |
Thunderbird 2.0.0.23 (X11/20090821) |
Hi Jamie,
in OpenEXR files the "chromaticities" attribute defines the color
space of the pixels. The attribute specifies the CIE (x,y) coordinates
of the red, green and blue primaries and the white point. By default
that is, if the chromaticities attribute is not present, the primaries
and white point specified in Rec. 709 (Rec. ITU-R BT.709-3) are used.
OpenEXR images are meant to be "linear" and "scene referred." The
values stored in the pixels are proportional to the amount of light
in the depicted scene. There is no gamma, and the images have not
been color-rendered.
The OpenEXR sample image collection includes a couple of files that
may help you test your code. The Chromaticies subdirectory contains
four versions of the same image, encoded in different ways:
Rec. 709 primaries and white point, RGB
Rec. 709 primaries and white point, luminance/chroma
CIE XYZ primaries, equal-energy white point, RGB
CIE XYZ primaries, equal-energy white point, luminance-chroma
As Lars Borg mentioned, the chromaticities attribute is not enough
to uniquely specify what an image is meant to look like when it is
displayed. One possible solution to this problem is described in
this document: http://www.openexr.com/UsingOpenEXRandCTL.pdf
Regarding some of the other comments in this thread:
- Storing gamma 2.2 encoded pixels in an OpenEXR is a bad idea; image
processing software does not expect this encoding, and there is not
even a generally agreed-upon way to specify that the pixels have
been encoded this way.
- The white point in the chromaticities attribute defines the
"relative strengths" of the RGB primaries.
Florian
Jamie L. Finch wrote:
I am working on loading and saving color space information in several
file formats.
JPEGs and TIFFs contain a tag to know of the image was created as sRGB
or Linear.
What I want to do is identify the color space of the loaded image and be
able to set
the color space when I save the image. Common color spaces are Linear,
sRGB
and rec709.
I would like some sample openexr images with color space setting in them and
any documentation about the color spaces.
Jamie Finch
Senior Programmer
NewTek, Inc.
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- Re: [Openexr-devel] Color Space Settings, (continued)
- Re: [Openexr-devel] Color Space Settings, Michael Wolf, 2010/03/21
- Re: [Openexr-devel] Color Space Settings, Deke Kincaid, 2010/03/21
- Re: [Openexr-devel] Color Space Settings, Michael Wolf, 2010/03/21
- Re: [Openexr-devel] Color Space Settings, Bob Friesenhahn, 2010/03/21
- Re: [Openexr-devel] Color Space Settings, Kai-Uwe Behrmann, 2010/03/21
- Re: [Openexr-devel] Color Space Settings, Lars Borg, 2010/03/21
- Re: [Openexr-devel] Color Space Settings, Michael Wolf, 2010/03/22
- Re: [Openexr-devel] Color Space Settings, Jamie L. Finch, 2010/03/21
Re: [Openexr-devel] Color Space Settings,
Florian Kainz <=