CODEWITHSUNDEEP
colorsrgbcomplement
math
math

Reputation: 8850

Given a gray value, what color provides highest visual contrast?

Assume that I've a gray image, and I want to draw e.g. text on it. Now the image has some dark and some bright regions. So if I choose for every character a separate color, in what way do I compute such a color to gain highest contrast of the text?

A pragmatic approach is to use yellow. (I don't know why, but its often used for subtitles in movies and documentaries) Furthermore I could darken the yellow in regions of bright background, and highlight it in regions of dark background. But this may provide some layer-effects.

I know that the color space may be important. I start with an RGB gray value, but LAB, HSV, or HSL may be better suited to compute the optimal color.

EDIT: As there was the question for a useful use-case: I really do not want to paint letters of text in different color. It is about color choosing for particular glyphs on gray textured background. (E.g. an MR image.)

Upvotes: 3

Views: 3411

Answers (1)

Jere
Jere

Reputation: 3397

The simplest answer to your question is to maximize the distance between the background and your text color.

If you convert to HSL, you can do this by maximizing the distance between L (V in HSV). And all that requires is to select white when the background lightness is less than 50% and black otherwise. Here is an example: http://jsfiddle.net/E2kU4/

if(bgLightness < 50){
    color = "white";
}else{
    color = "black";   
}

I think that pretty much solves it, but on to a few other points:

I'm not sure what the use case is for this. A word with different colored characters might look really bad. Typically, subtitles select a single color for consistency.

Yellow does stand out against a black and white image because of its saturation. Furthermore (and I'm not sure how to put this into words exactly), yellow has a really high chroma compared to other colors with similar lightness. It is best demonstrated on the HUSL page; by the way, HUSL is a great library for creating readable colors.

Yellow easily contrasts with dark colors because it is very light. It doesn't contrast with light colors as well, but that is usually solved by adding a shadow/outline in subtitles. Another example: http://jsfiddle.net/E2kU4/1/

But you can apply the same technique (of applying a shadow or outline) to the black/white example for maximum contrast. Now, the outline has the maximal contrast against the text. The outline stands out from the background too, unless those colors are similar, in which case the contrast is already extremely high (e.g. Near black background, black outline, white text) http://jsfiddle.net/E2kU4/2/

Lastly, converting to and from HSL/RGB should be trivial. There are plenty of libraries to do it.

Upvotes: 1

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