I was adding some colors to a Windows application. A column was going to be colored in order to indicate groupings to the user. So in Photoshop i first selected some colors to use. Being mathematically (rather than graphically) inclined, i chose to use the hue from every 60 degrees:
Note: This question is going to be about color theory; and less about graphic design or usability.
Since i was going to have to have Black text (e.g.
13 of 27) over top these colors, i needed them to be fairly light. I know that the L value in Photoshop refers to the human's intrinsic sense of how "light" the color is. I chose a Luma of
90. So with more fiddling in Photoshop i adjusted the L of each color so each had a Luma of
Note: i'm going to use L, or Luma interchangeable. i know there are precise, and separate, definitions for L, L*, Luma, Luminance, brightness, and lightness. Some definitions may be precise, some not. Lets avoid that holy war and just know that i'm using the L thing in Photoshop. And lets assume that two colors with the same L in photoshop will have the same apparent "brightness", or "lightness" to them. Again, forgive brightness and lightness. Yes, i'm inadequate.
As i change the L value, the Hue would change. So it was juggling act. Adjust the L, fudge the hue back to the value i want, adjust up the L, fudge the hue back, fudge the L, fudge the hue:
Eventually i get the hue i want to have the L i want.
But what saturation?
The code i was updating also used "gray" as one of the colors that could be shown to the user. I realized that grey doesn't fit into any of my hues. Intrigued, i added to my photoshop doodle. It's simply a "saturation" of zero (which is the S knob in Photoshop):
So then the question dawned on me. I decided to use a
Luma=90 for all my colors. This means that visually/psychologically/perceptually all the colors would be equally "bright". I've pinned down a Hue i want, and i've pinned down a Luma i want. But what Saturation do i want?
Ideally, and i don't know if this is a thing, they could all be equally "colorful". i don't want them to all be gray, i want them more colorful than that. And i want them to all the the same "colorfullness" - if that's a word.
So i did what anyone would do, i googled
wikipedia colorfullness, and there's an entry:
In colorimetry and color theory, colorfulness, chroma, and saturation are related but distinct concepts referring to the perceived intensity of a specific color.
- Colorfulness is the degree of difference between a color and gray.
- Chroma is the colorfulness relative to the brightness of another color that appears white under similar viewing conditions.
- Saturation is the colorfulness of a color relative to its own brightness.
Though this general concept is intuitive, terms such as chroma, saturation, purity, and intensity are often used without great precision, and even when well-defined depend greatly on the specific color model in use.
And then the article devolves into CIE, Lab, Luv. And i don't know what i want.
I went back to Photoshop, and started to just increase the "saturation" knob of each color. For a given hue, and the fixed luma, i increased the saturation in 5% increments (having to do fiddling along the way):
But at some point, the colors cannot "saturate" anymore without losing Luma:
And some colors can reach all the way to the end with
Which brings me to my question
In the same way the Luma defines the perceived "lightness" of a color:
is there a metric for the perceived "colourfulness" of a color?
Is there such a metric? Is the Saturation in Photoshop's HSB color model a perceptual one?
i noticed one snippet in the wikipedia article that's easy enough for me to understand: use the hypotenuse of
i could do that, and figure out which of my color chips have the same "Chroma".
In the end, in the real application, i used a color wheel centered around blue 210, and avoided green (in case the user things green means good), and use complimentary colors as much as possible.
But i still want to know about the color theory of "colorfullness".
Bonus ab length
Assuming the magnitude of an ab vector in Lab color model, i.e.:
- colorfulness = Sqrt(a2 + b2)
i calculated the chroma lengths of various colors:
Colors of different hues with approximately the same "chroma lengths" look to me like they have the same "colorfulness". If nothing else comes up, i might go back and recalculate all my existing constants using this formula.
Otherwise it will nag at me.