Didn't Michael Smith comment "is the population growing colorblind?"
Didn't Michael Smith comment "is the population growing colorblind?"
Thanks,
Kirk
at age 73:
"The woods are lovely, dark and deep,
But I have promises to keep,
And miles to go before I sleep,
And miles to go before I sleep"
To clarify my point, LAB any any RGB color space have different gamuts. And both are limited to a finite # of tones by the number of bits. Therefore during conversion from RGB to LAB, a specific tone in the source color space may not exist in LAB; that tone will be shifted to a nearby tone that LAB identifies (similar in some ways to converting from Prophoto RGB or Adobe RGB 1998 to Adobe sRGB; Adobe sRGB does not contain all the tones of the larger color spaces so those tones must be shifted if they exist in an image if it is converted to ADobe sRGB). When converting from LAB back to RGB, the same phenomenon can occur, and the tone can actually be shifted further away from the original tone. So tones can and do shift with every conversion.Originally Posted by Kirk Gittings
I'm sure that I'm not as expert as the other people who have answered this post, however my understanding of the problem in using the Hue/Saturation control in RGB is somewhat different. From my reading about this subject, as well as practical experience, the RGB Hue/Saturation control affects the luminosity of the tones adjusted as well as their saturation. (My understanding is that this is because of the way the RGB colour space is defined but it may be a quirk of Photoshop). In LAB, saturation and luminosity can be adjusted seperately, albeit that you have to manage the A and B channels to adjust the saturation, something I find less than intuitive. Using Joe Holmes Chroma Varients allows the saturation to be adjusted in RGB without affecting luminosity as it is the image profile (i.e. its mapping within the colour space) that is changed rather than individual pixels within the image.
Having said all of that I must confess that I still use the Hue/Saturation control for the usual small, and often local, changes requred during processing of an image. I have used LAB to assist in the separation of similar tones in rocks and very occasionally have used Joe Holmes Chroma Varients when I have wanted to make a major change to saturation (generally incremental desaturation of Velvia 50 in my case!)
If you are interested in using LAB colour then I suggest reading: "Photoshop Lab Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace" by Dan Margulis. It is a surprisingly good read and one of the most useful Photoshop books I have read, although I suspect this all shows I should get out more!
The advantage of using LAB is that by steepening the A and B curves you are increasing contrast along the magenta-neutral-green and yellow-neutral-blue axes. When used in moderation you therefore get separation of subtle tonal gradations.
The saturation slider, does nothing more than drive all colors towards their fully saturated prototype (red, green, blue, cyan, magenta, yellow, black, white). So you're more likely to see posterization and loss of color gradations with saturation, especially with saturated colors near the edge of their gamut.
When shooting RAW images with a digital camera, using the saturation slider in the RAW converter is probably the safest. Otherwise, my preference is LAB but for subtle tweaks it probably makes no difference.
dw,
I just ordered it yesterday. ThanksIf you are interested in using LAB colour then I suggest reading: "Photoshop Lab Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace" by Dan Margulis. It is a surprisingly good read and one of the most useful Photoshop books I have read, although I suspect this all shows I should get out more!
Thanks,
Kirk
at age 73:
"The woods are lovely, dark and deep,
But I have promises to keep,
And miles to go before I sleep,
And miles to go before I sleep"
Option 1:
1) Convert image to LAB (and flatten in the process (Bad))
2) Create curve layer
3) Select A channel
4) create S curve
5) Select B channel
6) Create S curve
7) Convert image to RGB (and flatten in the process (Bad))
8) result = increase in saturation; luminosity not affected; more separation in mid tones; potential shifting of tones due to conversion from RGB to LAB to RGB; no layers left
Option 2:
1) Create curve layer
2) Change blending mode to "Saturation"
3) create S curve
4) result = increase in saturation; luminosity not affected; more separation in mid tones; no shifting of tones due to conversion of RGP to LAB to RGB; All your layers left to tweak or rework if desired
Option 2 yields same result with fewer steps, all your layers intact, and no shifting of tones.
Excellent book. I highly recommend this as well.
As far as Joe Holmes profiles go it's best to get it straight from the horse's mouth:
http://www.josephholmes.com/news.html
A very worthwhile book for color work.
Greg, option one I was familiar with. Option two looks like it is a very useful "go to" kind of tool with allot of control. I will have play with it some more.
Thanks,
Kirk
at age 73:
"The woods are lovely, dark and deep,
But I have promises to keep,
And miles to go before I sleep,
And miles to go before I sleep"
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