Automatically change text color to assure readability

Question

Users can set the background-color of a button through a textbox that accept RGB hexadecimal notation: ff00ff, ccaa22, etc. So I need to set the te

Answer 1

You could use this simple schema to achieve that goal. Just convert the color from RGB to HSV form. You can use this link . Then use this pseudo code;

rr = (color>>16)&0xFF;
gg = (color>>8)&0xFF;
bb = color & 0xFF;

someBrightColor = 0xFFFFFF;
someDarkColor = 0x000000;

hsvColor = rgbToHsv( rr, gg, bb );
//
//hsv is array: [h,s,v]...all values in [0,1]
//
//color is from dark range, if hsv < 0.5, so we need bright color to draw text, because    in dark color bright color 'will be more visible'.  
if( hsvColor[2] <= 0.5 )
  textColor = someBrightColor ;
//this is opposite case , when in more bright color, the dark color 'will be more visible'
else
  textColor = someDarkColor ;

Also you could divide [0,1] range into more parts. And instead of defining 2 colors (someBrightColor,someDarkColor) , define more colors. My suggested method is 'how bright is background color , thas text color must be dark, and vice versa'.

Answer 2

A bit late to the party, but IMO all text should either be light or dark. Colored text is for links.

Here's a coffeescript function I've written to decide which to use:

is_light = (hex_color) ->
  c = hex_color.replace(/^#/,'')
  sum = parseInt(c[0]+c[1], 16)
  sum += parseInt(c[2]+c[3], 16)
  sum += parseInt(c[4]+c[5], 16)  
  log "sum is #{sum}"
  sum > 382.6