| Brightness weighted | This applies a brightness weighting according to the following formula, where ic = the calculated brightness value and exp the exponent, the function returns a
percentage that is then multiplied by 255:
var c = ic/255.0;
if ( c <= 0.04045 ){
return c/12.92;
} else {
return Math.pow(((c+0.055)/(1.055)),exp);
}
|
| like PS | Approximates to the greyscale calculation formula used by
Photoshop. red_value × 0.2235, green_value × 0.7154, blue_value × 0.0611, each in turn passed through the inverse gamma formula:
var c = ic/255.0;
if ( c <= 0.04045 ){
return c/12.92;
} else {
return Math.pow(((c+0.055)/(1.055)),2.4);
}
then the
result vi passed through a gamma formula as follows, which returns a percentage
that is then multiplied by 255:
return vi<=0.0031308 ? vi * 12.92 : 1.055*Math.pow(vi,1.0/2.4)-0.055;
|
| W3C YIQ | YIQ coefficients also known as Digital CCIR601 and suggested in the Web Accessibility Guidelines from the W3C and challenged by me (see Holes in the W3C Colour Readability Guidelines. ) red_value × 0.2125 + green_value × 0.7154 + blue_value × 0.0721 |
| YIQ Sqd | sqrt((0.0.2125 * red_value^2) + (0.7154 * green_value^2) + (0.0721 * blue_value^2)) |
| CIE XYZ | red_value × 0.299 + green_value × 0.587 + blue_value × 0.114 |
| XYZ Sqd | sqrt((0.0.299 * red_value^2) + (0.587 * green_value^2) + (0.587* blue_value^2)) |
| Lightness | ½ × (max(R,G,B) + min(R,G,B)), see Puzzling Greys. |
| Average | (R + G + B) ÷ 3, see Puzzling Greys. |