Join Deke McClelland for an in-depth discussion in this video Device-dependant CIELAB D50, part of Photoshop CS3 Mastering Lab Color.
Now, that we know based on the previous exercise, now that we know how the device dependent color spaces work that is RGB and CMYK. How does the device dependent color space Lab or Lab as I prefer to call it, work. Well, we are still working inside of this document called the Big Three.psd, it's found inside the O1 What It Is folder and I'm going to reveal the final Layer Comp which is this guy right down here Lab and the specific variety of Lab that is used by Photoshop is this guy right here. It's called CIE and CIE, by the way, stands for the group, the group that created this color space and they are the Commission Internationale de l'Eclairage and that's what four years of French gets you, people.
Obviously that wasn't my best subject but anyway in English- that's why it's called CIE by the way- in English that's the International Commission on Illumination which would be ICI but still same group and it's called L*A*B with asterisk between the L, the A and the B because this was actually the second variety of Lab that was propounded and this variety came out in 1976, the specs for this Lab space. Before that we have this guy Richard Sewall Hunter. In 1948 he began crafting this what he was calling the Lab space and you can know a little more about it actually by going to www.hunterlab.com and that is Hunter Lab.
Because this is the Hunter Lab, the hunter laboratory, which is why I prefer to call this color space Lab. Because it did actually start with a lab once upon a time, contrary to what you may have read elsewhere and also I just think calling it the Lab color space makes it a little less pretentious because RGB, we are not going to pronounce that RiGaBa and it also stand for something, it stands for Red, Green and Blue and CMYK, you could say Ceemic, I have heard people say Ceemak, which is ridiculous frankly. It's C-M-Y-K; it stands for something, the Cyan, Magenta, Yellow and Key, color black there.
Well, Lab doesn't really stands for anything. The L stands for Lightness but the A and B they are just variables essentially for two different opposing color axes. Alright, anyway then there is D50 right here. So we have got CIE, Lab, D50 and the reason that this is D50 is because you can define very specific L-A-B color values and why it's D50 is because you need a white point in order to define the Lab color values and have to mean something. You have to setup a white point in advance and the white point that Photoshop uses is D50.
That is 5000 degrees Kelvin, which is a bright sunshiny day. If you don't care, you don't care. It doesn't really matter that much but that's what's going on with the Lab as it is defined inside of Photoshop. So, it's a very specific definition even of Lab because there are different Lab values you could be working with. In a very general way, what's going on? Well we have lightness, which is the luminance information. This gradient right here looks just like the black ink gradients but it's actually different in terms how it behaves. It's the darkest to lightest color inside of the image then this was one of the key things about this particular variety of color.
CIE, this group, the Commission Internationale de l'Eclairage, they go way, way, way back, and they had some other device independent color definitions like XYZ and stuff going on back in the 30's. But Lab was the first one that was perceptually uniform, meaning that each increment, each increment that you raise the Lightness value by was going to deliver to you something that looked incrementally lighter. So, each increment looked liked it was uniformly lighter. Because the way that we see colors and the way the computers represent colors, the way that any hardware device represents color, is very different.
If we were to just go with what the computer considers to be uniform, we would get a very, very dark gradient that would have a mid-point right about here actually and then suddenly go white on us. In order to make it look nice and uniform for us though we have Lab. We have this special treatment of the lightness information and then we have got the color information represented by two, as I was saying, two opposing color axes, one of which is A, which is our Tint information. If you are familiar with Camera RAW or Light Room, they have got Tint controls and that Tint control is the same as the A information here.
So we go with dark color inside of this channel, we get green or a greenish color. It's not really green; it's more of a turquoise. I will explain that later. Goes through to a neutral gray right there in the center and then we, with a positive value, as we will see, we go over to magenta or red, you will sometimes here it called red as well. So, green, red, green and magenta, what have you in the A channel and then for the B channel we have blue, yellow and that's your temperature information. Once again Temperature is how it's represented inside of Camera RAW or Lightroom and that's how we get L-A-B.
Now, I have yet to answer the bigger question, which is how in the world do these colors mix to form a full color image? You might be able to imagine how RGB works maybe or CMYK, but Lab, it looks like these things mix to form mud and I'm going to answer that question, but of course in the following exercises, just to give you a sense of how this is going to work. In the next exercise, I'm going to explain how the numerical color values work inside of the Lab space, something that we have to understand and very exciting. But we have got to understand what's going on there and then in the exercise after that we will see the big Lab color wheel where all of your colors will be shown to you right before you there on screen and then we will start examining the independent color channels.
It's exciting stuff. It's really, really interesting, I swear to you. Stay tuned.