"DL" wrote in message
Chris,
I agree that my printer can only accept RGB data, and that converting
between
RBG, CMYK, and back again can result in image degradation. That’s what motivated my original question, which was how can I do this with minimal
or no
loss?
Every image has 10 channels as Dan Magulis points out in "Professional Photoshop." (That’s RGB, CMYK, and the 3 Lab channels if that’s not
obvious.)
No, you’re missing the point of what Margulis really meant. What he means is every image can be manipulated using whatever colorspace you want, and in the the case of PS that offers you a total of ten channels. But, and this is point you’re missing, every image *starts out* in one, and only one, color space.
CMYK and LAB are not "hidden" channels in an RGB image. They don’t exist until you actually convert the file. For example, the only way you can get from RGB to CMYK, or back the other way, is by converting. If we assume no gamut clipping, whether or not that conversion will *visually* degrade the image is debatable, but it *will* degrade the image due to rounding errors. Those errors are a fact of conversion, and there is nothing you can do about it. Not even Margulis denies this.
Now, fwiw, I’ve read that the conversion (in PS) from any space to LAB and back causes the least damage since PS apparently uses LAB in the backgound for all images. I’ve never seen anyone like Chris come right out and say that, however, so take it with a grain of salt. In any event, many experts suggest using LAB conversionws, or adjustment layer modifications (eg, fade) to take advantage of the attributes of working in LAB (especially the use of the Luminosity channel) since there is so little "damage." Like I said, though, I’ve got no proof of this.
There are a number of powerful color correction techniques described in
that
book requiring a trip into CMYK. I want to have the CMYK tricks in my bag
, but
not suffer the image loss you might see. The Wide Gamut CMYK profiles
should
one to do that.
There are those who think it (CMYK) can be a valuable tool for RGB images, and Margulis is obviously among them. Then again, there are well known authors and PS experts who think it is totally unnecessary and simply slams the file for no good reason. Thus, I guess it goes without saying that Margulis has his disciples as well as his detractors.
By all means, give it a shot. Try it for yourself, make prints, and be critical.
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