Determining Color Difference Using the CIELAB Model?

Colour Blind asks: "I am working for a not-for-profit organization developing a website for kids. I am attempting to develop a method for testing if two colours (as defined by R, G, and B values [0-255]) are adequately different to be visible on top of each other. So far I have tried many things but this is the one that, by all accounts, should work: I have converted from RGB to (CIE)XYZ using a 3x3 matrix transformation. From here I have used three more equations to convert to CIELAB colour. I have then calculated the distance between the two colours in question in CIELAB colour space. The results are not correct: there are pairs of colours that are quite far from visible that yield the same difference as colours that are plainly acceptable for visibility. Any suggestions?"

Comments

Try the Value in HSV instead

["Zow"]

I think the key in picking colours for any website is that they have have a difference of at least X in brightness (the V in Hue-Saturation-Value unless I'm sadly mistaken - I'm not an expert in this area), where you should be able to determine X experimentally. Any decent color picker (such as those in Gimp or Photoshop) will allow you to jump between RGB or HSV. The reason I think this is the way to go is that a decently large percentage of the population (at any age) is colour blind, so while you or I may easily be able to see the difference between a blue and green, or a green and red, at the same brightness, some people (particularly males), just can't.

That should take care of you for making the site usable. At that point, the choice of which light or dark colors you use for what becomes purely stylistic (again, I'm just a stupid computer scientist - I'm sure someone with a stronger HUI, marketing, or fine arts background might have a stronger opinion on what colors are used for what).

-"Zow"

Re:Try the Value in HSV instead

[sfraggle]

I have to agree with this. I am the author of Text Mode Doom and I hit a problem along these lines during development: the RGB value itself is not particularly useful when trying to find a numerical value for a particular "colour" that the human eye perceives. In text mode doom I was faced with the problem of mapping the particular colour value to a corresponding text colour, of which I was limited to a small value (under 16). I solved the problem by converting the RGB values into HSV and then assigning text colours to the real colours based on their hue. The results I found with this were quite impressive

Land's Two Color visual perception work

[mbone]

Edwin Land (yes, the founder of Polaroid) did work in human color perception, where he showed that two colors could used to create an apparent full color image.

The important things are our visual expectations, as well as the relative intensity of parts of the scene. I can remember a demo from Land where two projectors sufficed to give a full color scene. If part of the image was abstracted, it appeared to be black and white ! This implies that a combination of two colors can, under certain circumstances, appear to be the same as a different combination of three colors. I would suspect that this effect would have to be considered in the vision tests described in the original posts.

A Michigan State U. report on the Land work is available, as is a lot of more recent work, such as this paper by Kobus Barnard.

Why not ask the kids?

[MarkusQ]

Why not ask the kids? Make it a game of some sort (details depending on age) where they have to find and click on some target word or image. Track how often (or how quickly) each combination is picked, and you'll have all the data you need to answer your question. To keep from wasting time in the parts of colour space where you know the answers (yes, navy blue text shows up well on a pale pink background) have the game advance through levels (each level having less distinction than the one before) until they have three wrong clicks/timeouts. Then start over with another base colour pair.

-- MarkusQ

Re:Color blindness

[BWJones]

Yeah so this was interesting as there have been tetrachromats discovered in other primates (monkeys other than humans), so it was reasoned that it might be possible to find tetrachromacy in humans.

The advantage that hyperdimensional color perception has over traditional trichromacy it a better ability to discriminate hues or different colors. Therefore a tetrachromat could be considered to be at a certain advantage when it comes to color discrimination. This obviously has not been important to our evolution but it is for some species as birds and turtles see a world we can only imagine with some birds seeing from ultraviolet into the visible spectrum and turtles seeing a world rich with color. For instance, if you were to imagine a turtle sitting in a pond with the water as still as glass and the sun setting on the horizon making everything (the sky, land and water) red and orange and yellow, the turtle sitting in the water would be able to pick out a frog sitting on a log with discrimination that we could never hope to approach.