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We are now going to work with the Lab Color version of the same image. I am going to convert this RGB image to Lab Color, using the Mode menu. When I do so, the file size will not change. We still have three channels as we did when with the RGB image. They are now called Lightness, a, and b. Lab Color is a device independent color space. Unlike RGB, unlike CMYK, the properties of the color are not tied to specific color profiles, which describe the range of colors that can be displayed or describe the properties of the output device that the file is being sent to.
If we just go and have a look at the color profile right here, regardless of how this started out, when you convert to Lab Color, that's the color profile that you are going to have. So what are the implications of this? What does Lab Color mean for us? Unlike a mode conversion between RGB and CMYK, or the opposite, converting to Lab Color is not destructive. So we can go to Lab Color and then we can go back to RGB or to CMYK, we don't lose anything.
Not all of our filters will be available to us. You will see that we don't have the Filter Gallery, Lens Correction, Vanishing Point, the Sketch Filters, none of those can you use in lab. Let's have a look at the qualities of the different channels. The Lightness channel is very easy to understand. This is just a grayscale version of the image. And before the Black & White adjustment which is right there, or also exists as an adjustment layer, before the advent of the Black & White adjustment, converting to lab, and then discarding the a and the b channels was perhaps the best way to get good quality grayscale from a color image.
So the lightness is easy enough to understand. The a and b channels however are a little bit more tricky to understand. The a channel if I turn that on, is on a magenta to green scale and if I now turn on the b channel, that is on a yellow to blue scale. I'm now going to turn on all of my channels in terms of editing a lab image. Because it is device independent, because it has the biggest color gamut of all the color spaces, indeed all the other color spaces are essentially subsets of lab, some people prefer to do their editing in lab.
I am not one of those people because I think it's a very difficult color space to get your head around. Lightness as I said easy enough. This is on a scale of 0 to 100, and when we come to a curves adjustment for a lab image, you're editing the channels one-by-one. There is no option to edit them as a composite as you would have in RGB, and with CMYK. So if I move the curve up, things get brighter, move it down, things get darker.
If I go to the a, if I move up, then things get more magenta, move down, things get more green. And the b, move the curve up, things get more yellow, move down, things get more blue. So, if you're fearless and want to edit your images in lab, the advantage of working in the lab color space is that you're working with the maximum number of colors available in your image, and you would then need to convert the image to a CMYK image if you are going to be printing it on an offset printing press or to an RGB image if you're printing it on a desktop inkjet printer, or if you are going to be making a screen image.
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