Convert to profile or image mode?

Discussions and questions about Dan Margulis's LAB Color Book
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Joined: Fri Jan 26, 2007 1:24 pm

Postby derekfountain » Sat Aug 25, 2007 11:15 am

On page 44 of the LAB book, Dan says he goes from RGB to LAB using Edit -> Convert to profile, whereas I've always used Image -> Mode -> Lab Color. He describes his view on dithering, and that he uses the simple option to go to CMYK mode, but not why he doesn't use the simple option for getting between RGB and LAB.

Why is Edit -> Convert to profile preferable to Image -> Mode -> Lab Color for getting to and from LAB mode?

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Postby -default » Tue Aug 28, 2007 8:37 am

On the same page of the book, Dan discusses his  reasoning a bit more.

It's probably more desirable to not add gratuitous noise to the image, particularly when you are doing more than one conversion.  "Convert to Profile" gives you more control.  It allows you to turn off dither, and avoid adding noise multiple times to your image.  This extra noise could be significant if you perform any major sharpening or contrast enhancing curve moves.

The Image Mode commands don't give you this choice, and always add fine noise (dither) with each conversion. 

Dan prefers to add noise when converting to CMYK - so Image Mode is the way to go.  An argument could be made for using dither when converting back from Lab.

Personally, I use Image Mode in both directions, but now that you've asked the question, I will reconsider this.

BTW, Curvemeister never uses dither for its conversions.

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Postby mikemeister_admin » Tue Aug 28, 2007 11:43 am

Thank you Mike for the explanation - it was something I had puzzled over as well as Derek.

I guess the answer is to try both ways and see if one can spot the difference.  I certainly sometimes find a fair bit of noise in the sky after playing around in Lab - which I then have to remove.  So next time I notice that I'll rework the profile way and see if things are better.

Can one ask how v3 is coming on - or have you had a restful summer?

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