Concerning the video I shared two posts back.. Here is a Quote from Mark Caudrey concerning that video and the science of color from another Industry forum.
Quoting Mark
Normally I tend to stay out of the forums, but occasionally something really interesting comes along and I'll dive in, usually to my regret. I hope not this time. This is a really nice video and I agree with much of what is being said. HSB has been a really wonderful space to calculate color in, and in fact we have been doing it very, very successfully since 1994. The most powerful (and expensive) separation program on the market is ICISS. It is entirely HSB based and has been since it was released commercially in 1995. We were instrumental in the design and development of it and it is the basis for NetSeps.com color separations. Well over 50,000 high end seps have been delivered to printers since we started NetSeps online in 1999.
I think there needs to be some clarification about HSB compared to sRGB, Adobe RGB, and all the other color spaces. The key word here is "color space." There are dozens of color spaces: sRGB, RGB, HSB, HSL, LCH, L*a*b*, XYY, XYZ, YCH, and the list goes on and on. All of them are derived from XYZ which is modeled after what the human eye perceives. To get the values, the CIE uses what is called the Standard Observer. This is comprised of averaged perceptual visual data response from 2000 healthy people under specific color viewing conditions. All of the other "spaces" are mathematical derivations of the human response.
So. . . all very complex, very techie. What does all this mean? Simply, every space contains some subset of what we can see. In some cases (YCH) the space is actually bigger than what we can see. In the case of SWOP CMYK or sRGB, the pigment values being used to represent the gamut are the limiting factor to how much color we can reproduce.
Why do we choose one space over the other? The answer is very, very simple. It's about how color interaction is calculated. The shape of the gamut makes is easier or more difficult to calculate. The goal is measured color in = measure color out. What You See Is What You Get, not a guess based on some arbitrary overlapping extraction of color.
If you look at the shape of the gamut in Tom's example you'll notice it looks like an inverted iceberg. Very difficult compound shape. The computer uses complex mathematics to take this continuously changing shape and blend the values accurately. It is flippin crazy complex.
When we were developing ICISS, it was necessary to hire two PhD mathematicians to interpret the printed data, develop the algorithms and then make it usable. It amounts to continuous 3D calculus. I've taken calculus and know how to use it, and it was WAAAAYYYY beyond anything I had ever done. This is one of the reasons that program is so expensive. There is REAL math and science behind it, not just color extraction.
If you look at the wire frame in Tom's video, the process in the past has been designed to break the gamut into polygonal shapes and calculate the color of each shape. Much easier to do, but not all that accurate as color does not easily blend. You are essentially calculating panels of color between color.
Spaces like L*a*b* and HSB are essentially represented as spherical shapes that are much easier to calculate with less distortion and color shifting. No matter what color space you are using, some distortion will occur BECAUSE the human eye does not perceive color precisely based on the calculations. All color separations are based on relative color matching (as in one color relative to the next color)
The human eye sees things based on human perception, and there are gliches and errors in the correction. We have a mental short circuit with some colors. For instance, if you add black to yellow you do not get dark yellow, you get muddy green. Look at the Pantone book on the page that has Pantone 109 and look at what happens to the yellow as it moves to 110, 111, and 112.
The reason we chose HSB way back in '93-'94 was because it was the space that's easy to conceptualize for an artist. Most artists are not programmers or mathematically inclined. The computer calculates color as a set of 3 numbers .
H= Hue = Color Name = 0°-360° as in a color wheel that everyone knows. We call the number assigned to the H value the Hue Angle for that color.
S = Saturation = Purity of the color = 0% (no color) - 100% (pure color.),
B=Brightness=Emissive Value of the Pixel on the monitor = 0% (black) -100% (full color value). Emissive means light behind. It is not "reflected" light value. For printing on BLACK or colored backgrounds HSB is the ONLY color space that can be used to get the correct underbase values (but that is an entirely different story for another time.)
So using this example. The Hue Angle starts at 0° (red) and moves clockwise back to 360° (Red). Primary colors and their compliments are located 60° apart. Red- 0°/360°, Yellow-60°, Green-120°, Cyan-180°, Blue-240°, Magenta-300°.
You can use the color picker in Photoshop to learn how to see and visualize any color as a number by selecting a color with the eye dropper and then looking at the HSB values in the Color Picker window. I have attached the HSB for Pantone 109 as an example.
We recognized to accurately color separate, you had to be able to "see" a color and mentally be able to convert it to a series of numbers the computer could map and calculate.
So, bottomline. HSB is the most addressible space. When you have an addressable space, you can make better color decisions as to how the separation will proceed. I don't know how Tom's program works or if it's based on selection and ranging or if it does indeed have the ability to map a pigment against the actual values in the original so it will be able to reproduce accurately. Anytime you move from one space to the next, there will be loss in the process. The more addressible the color space, the more things we can do to compensate for the loss.
As a printer, all of this should be in the background. I am, and always have been a 100% proponent of the math and science behind everything we do. That is my job, to make sure the foundation assumptions are consistent with the higher laws of mechanics, physics, chemistry, math, etc. I am an engineer by nature and this is why I get excited when I see someone else figuring this all out.
You might ask why this has been kept "secret" for all these years. In reality it is no secret at all. I have never been the kind of marketer who sells his products base on a sales pitch or a bunch of marketing mumbo jumbo that can't be explained.
All I know is that it works better than anything elseand if you are really, really serious about color separation and getting great color you need to know how to "see" color as numbers and understand where you are going with it.
If we do our job right, each of you should be able to get great results without having to know too much about how you get there. For those who are really serious, you can download The Top Ten Quick Start Guide to Printing Halftones at
www.halftonesecrets.com. It's free. And for the REALLY serious, you can visit
www.HalftoneMastery.com for more info.
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