color space of image imported from JPEG

[James Walker]

Some JPEGs include color profile information, but some don't. If I
import a JPEG without color profile information using Image IO
(CGImageSource...), I get an image such that CGColorSpaceCopyName(
CGImageGetColorSpace( img ) ) returns the name "kCGColorSpaceDeviceRGB".
That constant seems to be undocumented, and I'm not too confident of
my understanding of color spaces, but tell me if these guesses sound right:

(1) That "device" in the color space name means that the image is likely
to look different on different machines.

(2) If I took the image and fed it to CGImageCreateCopyWithColorSpace
along with the generic RGB color space, it would do color matching to
convert to generic RGB (as opposed to pretending that the image was
generic RGB all along), and the resulting image would still be
device-dependent.
--
James W. Walker, Innoventive Software LLC
<http://www.frameforge3d.com/>
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[Michael B Johnson]

If there's no color profile, you (theoretically) have no idea what color space it's coming from, so you really know very little about how to map those RGB values.

In practice, I would assume an sRGB gamma 2.2 space and go from there. Your mileage may vary.

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[David Duncan]

On Mar 5, 2012, at 4:09 PM, James Walker wrote:

(2) If I took the image and fed it to CGImageCreateCopyWithColorSpace along with the generic RGB color space, it would do color matching to convert to generic RGB (as opposed to pretending that the image was generic RGB all along), and the resulting image would still be device-dependent.

CGImageCreateCopyWithColorSpace does not do color matching, it just replaces the color space of the given image. Basically its a re-interpret operation.

--

David Duncan

[James Walker]

Thanks, that helps.