It was 9/6/03 11:06 am, when michael shaffer wrote:
I have heard of the occasional task, for which "filtering" one of the Lab
channels was of some help, but I haven't heard of any advantage of using Lab
for tonal or color adjustments.
Dan Margulis devotes over 40 pages in his Professional Photoshop book to the
subject of correcting color in Lab so it obviously has *some* uses. As an
off hand example, if your image has a stubborn colorcast, moves in Lab will
remove them when other color modes will not or only if you spend an
inordinate time and employ workarounds and personal techniques that you may
have developed.
Hi Shangara and Michael,
I've read Dan's book at least three times at present, and would like to mention another method for using the LAB space, batch/droplet processing smaller images (so need for noise reduction in the A+B channels). The tonal moves come from the L channel with an auto contrast command applied, and the A+B channels require linear steeping in both to boost colour. As for sharpening the L channel with all that detail and no colour.
This has got to be a real money earner if you get enough of the work.
Personally, I wouldn't worry about moves to Lab and back, especially if your
image is in RGB mode. If your image needs fixing, there's more advantages to
moving to Lab and back than there are disadvantages. By definition, if you
are going to correct an image, you're going to lose something and gain
something so a move to Lab is not going to be 'detrimental' to the image as
such. Again, there are workarounds which allow you to stay in your image's
color mode and at the same time take advantage of Lab's unique color
mapping.
Dan's methods I mentioned above are mainly for smaller images going to CMYK, as the next step he suggests is to convert from LAB to CMYK. But the issue about changing spaces RGB-LAB-RGB is also stated in the book to cause very little damage, unless ones studying that crutch the histogram and not worried about whether the image looks better. If LAB is needed for larger images, the real advantage is for more extreme edits to poorer originals including colour moves and noise reduction in the A+B channels, the latter is where one can fade back to colour mode in RGB for the same effect.
I have been told recently though for my own benefit, that colour blending in RGB behaves differently with different gamma than the ICC LAB space and is possibly something to watch out for when performing some edits. Especially running actions, like the following, which is what I used to do in LAB. <g>
http://www.2morrow.dk/75ppi/coolpix/actions/
Christian Macey
P.S. I should also mention that it is possible to save out from Linocolor as TIFF LAB which seems a big advantage. And IMHO with the LCH editing mode, it seems Linocolor *HAD* a much better workflow when coming from a scanner for archiving in Photoshop.
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