I hate to ask a very open-ended question, but I've been wondering for some time whether it is worthwhile for me (a serious amateur) to learn about using LAB color space. I don't have any aversion to spending the time needed to learn new stuff. What I don't have a good sense of, however, is whether working in LAB will be useful often, occasionally, or ever. Accordingly, I'd be interested to hear from those who have an opinion on this topic. In particular, if you use LAB, I'd like to know what you use it for and how it may be superior to other approaches (such as using a luminosity blend mode, etc.). Many thanks for your responses.
It's always a good idea to pursue deeper knowledge, especially with a program like Photoshop with its myriad of features.
Lab color space separates color and brightness (luminance), making it possible to just make adjustments in color without affecting the tonal balance. It also allows you to sharpen an image in luminance without introducing color noise. The simplest and maybe the most often used adjustment is to steepen the a and b curves in an adjustment layer while in Lab mode to enhance color.
One of the interesting things in Lab is that you are working in a color mode that introduce colors not present in the original capture, but likely present in the original scene. This can be used to correct or enhance an image. The a channel contains red and green color information and the b channel holds blue and yellow. Once you learn how to use Lab, it is often easier to make adjustments to skin tones, deepening color saturation without making it look artificial.
Other approaches are perfectly valid, but some things are just so much easier in Lab once you understand it and get comfortable using it, especially in combination with the other techniques.
You might want to pick up some of the books by Dan Margulis, who goes into rich detail explaining how to maximize the benefits of working in Lab mode.
Posted by Garry Revesz on August 7, 2010 at 11:07 AM
Gene,
That's pretty interesting stuff. I haven't yet gotten to that level of fine colour adjustment in my images, although I have often wondered how I can enrich the colour depth I saw with my eyes but doesn't come through in the same way on screen, so I can see how it can benefit the end result. However..., what affect will that have on the colour space or gamut for printing?? Good question Phil.
From my understanding, most consumer level printers can print sRGB, a few more can print Adobe RGB, as can most printer services. Most analog monitors can display sRGB, some RGB, ditto for flat screens. If your process is color managed - in that you have profiled your monitor, printer and possibly your camera, then you should be able to get a good approximation of what you see on the monitor in your prints. You should think about rendering intent as well. Human vision is not that precise with color wavelengths, but pretty good at understanding relationships between colors, shades and saturation, which means that for the most part, your printing process should use a perceptual rendering intent.
Thanks for the responses. I'm actually surprised there hasn't been a bit more of a reaction to the post, but perhaps that's an indication that folks on this site aren't widely using LAB. Anyway, I will try to pick up a copy of the Margulies book . . . it's discounted pretty steeply on Amazon I notice.
Another advantage of Lab is that you can adjust luminance without affecting color--this is a big advantage, in my opinion. I haven't poked around with Lab much, aside from doing some sharpeniing using the 'Lightness' channel, but based upon some reading, I think I'll delve more deeply into it. I believe Michael Gordon uses Lab as a matter of course for his color work.
Lab is also the connection space that all our printer profiles and many of our monitor profiles use to convert to and convert from for all these different devices. So if you ever deal with the need to match certain colors precisely (graphic artists working with Pantone colors for example), it is really helpful to identify those colors in Lab space and then print from Lab space.
Personally I haven't found a convincing enough reason to use LAB, though I have played around with it and read a few chapters of Dan Margulis' book. The two most cited reasons to use LAB are separation of the luminosity and color channels, and more refined saturation enhancement. Well, I can do both in RGB, so why bother with another colorspace that requires me to flatten my image on conversion, making it very hard to keep a full record of all my edits (which is essential for quickly going back and making changes).
With blend modes it is easy to select color and luminosity channels to get the independent control (I've heard it's 'not quite the same', but if it looks and sounds like a duck...). You can achieve (IMO more pleasing) "saturation" enhancements using the channel mixer in RGB with the color blend mode. I use saturation in quotes, because using the channel mixer it's possible to boost colors without changing the overall saturation.
Thanks for the additional responses on this topic. Floris, your thinking pretty much mirrored my own at the start of the post . . . you can use luminosity and color blend modes to achieve the advertised benefits of LAB color space, or so it would seem, and thus the question arises of whether there's much to gain by switching over to LAB. Anyway, perhaps some experimenting is still in order.
Posted by Gene Lugo on August 13, 2010 at 12:04 AM
Well, unlike CMYK and RGB, Lab is device independent, allowing you to refine your image then convert to the other modes as required. As far as being able to do the same things in RGB as you can in Lab, while it is possible, some things, like color replacement, dramatic contrast enhancement without affecting color balance and vice versa, and conversion to black and white are all things that are done with more precision and with relatively greater ease than in RGB. Depending on what you are looking for, it might be worthwhile learning.
Posted by John Williams on August 13, 2010 at 10:40 PM
There are many areas where LAB is useful, but my two favorites are for color contrast and for restricting changes to certain colors.
If you have lots of color contrast to begin with, especially if some colors very saturated, LAB is overkill. But if you have low color contrast, LAB does an excellent job of separation. (Margulis named his LAB book The Canyon Conundrum specifically because LAB does so well with low color contrast canyon walls.)
I also commonly use LAB with the Blend If sliders to restrict an edit to a certain color range because it is independent of luminosity. For example, if you have a scene with both light and dark blue flowers and want to increase their luminosity and saturation, you get a very different effect if you use the blue channel of RGB as apposed to the b channel of LAB to restrict the effect using the Blend If sliders.
Discussion
10 repliesIt's always a good idea to pursue deeper knowledge, especially with a program like Photoshop with its myriad of features.
Lab color space separates color and brightness (luminance), making it possible to just make adjustments in color without affecting the tonal balance. It also allows you to sharpen an image in luminance without introducing color noise. The simplest and maybe the most often used adjustment is to steepen the a and b curves in an adjustment layer while in Lab mode to enhance color.
One of the interesting things in Lab is that you are working in a color mode that introduce colors not present in the original capture, but likely present in the original scene. This can be used to correct or enhance an image. The a channel contains red and green color information and the b channel holds blue and yellow. Once you learn how to use Lab, it is often easier to make adjustments to skin tones, deepening color saturation without making it look artificial.
Other approaches are perfectly valid, but some things are just so much easier in Lab once you understand it and get comfortable using it, especially in combination with the other techniques.
You might want to pick up some of the books by Dan Margulis, who goes into rich detail explaining how to maximize the benefits of working in Lab mode.
That's pretty interesting stuff. I haven't yet gotten to that level of fine colour adjustment in my images, although I have often wondered how I can enrich the colour depth I saw with my eyes but doesn't come through in the same way on screen, so I can see how it can benefit the end result. However..., what affect will that have on the colour space or gamut for printing?? Good question Phil.
Garry
From my understanding, most consumer level printers can print sRGB, a few more can print Adobe RGB, as can most printer services. Most analog monitors can display sRGB, some RGB, ditto for flat screens. If your process is color managed - in that you have profiled your monitor, printer and possibly your camera, then you should be able to get a good approximation of what you see on the monitor in your prints. You should think about rendering intent as well. Human vision is not that precise with color wavelengths, but pretty good at understanding relationships between colors, shades and saturation, which means that for the most part, your printing process should use a perceptual rendering intent.
--P
Patrick Herold
Tech Support
www.chromix.com
With blend modes it is easy to select color and luminosity channels to get the independent control (I've heard it's 'not quite the same', but if it looks and sounds like a duck...). You can achieve (IMO more pleasing) "saturation" enhancements using the channel mixer in RGB with the color blend mode. I use saturation in quotes, because using the channel mixer it's possible to boost colors without changing the overall saturation.
If you have lots of color contrast to begin with, especially if some colors very saturated, LAB is overkill. But if you have low color contrast, LAB does an excellent job of separation. (Margulis named his LAB book The Canyon Conundrum specifically because LAB does so well with low color contrast canyon walls.)
I also commonly use LAB with the Blend If sliders to restrict an edit to a certain color range because it is independent of luminosity. For example, if you have a scene with both light and dark blue flowers and want to increase their luminosity and saturation, you get a very different effect if you use the blue channel of RGB as apposed to the b channel of LAB to restrict the effect using the Blend If sliders.