On: All RGB colors in one image

[jacobolus]

HSV is just a straight-forward transformation of RGB https://en.wikipedia.org/wiki/File:Hsl-and-hsv.svg

The set of “all colors” is exactly the same.

(Note, HSL/HSV are not suitable representations for almost any purpose, especially not for human user interfaces; it’s a tragedy that they are in such wide use.)

[skeltoac → jacobolus]

A color space is good for transforming colors along lines orthogonal to its axes. In RGB, you can't easily find another shade of a given hue. In HSV, this common task is trivial.

[lstamour → jacobolus]

I was going to comment that HSL/HSV can be useful for generating colors that work well, but... the real problem is not luminance as much as the HSL values we commonly use. See http://en.wikipedia.org/wiki/HSL_and_HSV#Disadvantages where CIELAB L* is shown as a better representation. Though it's not perfectly matched to the human eye even so.

[jacobolus → lstamour]

> See http://en.wikipedia.org/wiki/HSL_and_HSV#Disadvantages

Yeah, I wrote that. :-)

[TylerE → jacobolus]

Whjy do you say that? I find them much more intuitive. For example, getting actually brown browns with RGB is tricky...with HSV it's trivial.

[nitrogen → TylerE]

A rule of thumb if you have to find brown in RGB: use a bit of red, slightly less green, then a tiny bit of blue.

[andrewflnr → nitrogen]

That kind of proves the point. How many of those rules of thumb are you going to have to formulate to express in RGB what's trivial to find in HSV?

[nitrogen → andrewflnr]

Unfortunately I've already formulated them after working so much with RGB in low-level graphics code, pre-hsv() CSS, and some image editing software.

Actually, that sounds kind of like a fun challenge game: name a color, then try to guess RGB values for that color.

[entropy_ → nitrogen]

I've gotten pretty good at doing the reverse operation(given an RGB value, guess the color) because I'm red-green colorblind and that's how I figure out what color something is :)

[robinhouston → nitrogen]

The converse game exists: http://yizzle.com/whatthehex/

Edit: Actually, so does the “guess the RGB given the colour” direction, but I don’t find it as fun: http://mallory.jemts.com

[roryokane → TylerE]

jacobulus might have been referring to certain color spaces that are optimized for human use instead of for computer manipulation, such as HUSL (http://www.boronine.com/husl/). HUSL gives you a slider that actually changes the apparent brightness of a color to your eye: whereas HSL thinks that bright green is just as “light” as dark true blue, and HSV/HSB thinks that true blue is just as “bright” as white, HUSL colors with the same “lightness” actually do look equally light. Another human-optimized color space is CIELUV (https://en.wikipedia.org/wiki/CIELUV).

[lcrs → jacobolus]

The mapping is not one-to-one though - for example when S is 0, all values of H give the same resulting colour, and worse when V is zero both H and S are useless. So an image exploring the full HSV space should look different, probably with a lot more of the grayscale.

I too have misgivings about HSV, the discontinuities created when generating hue ramps being particularly cruel. Using a rotation about the luma axis in YCbCr space gives much smoother rainbows but sadly not ones which hit all six primaries and secondaries. It's frustrating problem that perceptually H, S and V or L are what we think of when specifying a colour, but mapping them smoothly to RGB displays is so tough.