[Greg McKaskle]

As for using only hue, a white or black object in incandescent light may very well show 250 as well. The hue is an angular measurement by the way, and this is really just pointing in a direction on the color wheel saying (in the red family).

To continue my home improvement analogy for HSL, Let's say you are mixing paint. You add pigment to a base then shake the daylights out of it. The hue is the color of the pigment you add in. S is how much pigment you add, and L is the color of the base you start with (snow white, light gray, medium gray, dark gray, etc.)

So when you look at something like the target, it is clearly highly saturated, lots of color. If you take a little bit of that same color and add it to white paint, you'll get a softer color of exactly the same tint or hue. If you add it to gray paint, you get a pastel of the same hue.

As for being systematic, you can pretty easily do this for a particular lighting situation. You can take a few photos using the axis, and statistically measure the spread of HSL values that your target returns. You can decide how many additional std deviations to include for a safety margin. The problem is that when the lighting changes, your statistics aren't valid anymore. At least some of the numbers are not valid. Arguably, as you expose to additional lighting arrangements and types of lights and you merge the HSL sets you find, you ultimately wind up with the wide set of values the in the demo code.

So, are you asking because the demo code doesn't work well enough? Or because you want to tune it? Also, let me know if you are using LV or C.

Greg McKaskle