one fing leads . . .

Experiments with Brightness Ranges
Re-colour an image according to different brightness levels. Five brightness levels can be set to a specified hue. Purpose is for greater understanding of colour brightness and look.
Select picture
or specify image url apply
 will be converted to 800px × 600px – see copyright notice
 
 
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colour to replace where the brightness of the pixel is
0 to
 
 OMIT
 
 
 
 
 
Opacity %
 
         brightness: set to 49
 
colour to replace where the brightness of the pixel is
50 to
 
 OMIT
 
 
 
 
 
Opacity %
 
         brightness: set to 99
 
colour to replace where the brightness of the pixel is
100 to
 
 OMIT
 
 
 
 
 
Opacity %
 
         brightness: set to 149
 
colour to replace where the brightness of the pixel is
150 to
 OMIT
 
 
 
 
 
Opacity %
 
         brightness: set to 199
 
colour to replace where the brightness of the pixel is
200 to 255  OMIT
 
 
 
 
 
Opacity %
 
         brightness: set to 255
 
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There are different formulas for calculating relative brightness:
like PS
W3C YIQ
YIQ Sqd
CIE XYZ
XYZ Sqd
Lgt’ness
Average
 
brightness weighted
 
inverse gamma
gamma
: exponent
 
(Explanation of each formula at foot of page.)
 
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to filename: type:
There are many different ways of calculating greyscale, by multiplying the red, green and blue colour values by different fractions. These give different results.
The results can be applied linearly or with a brightness weighting. (For brightness weighting in graphic form, see Colour Brightness Experiment.) Brightness-weighted results will inevitably be darker by the nature of the curve, as shown graphically on Colour Brightness Experiment.
Brightness weightedThis applies a brightness weighting according to the following formula for inverse gamma, 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);
}
and the formula for gamma where v = the calculated brightness, returns a float between 0 and 255:
if(v <= 0.0031308){
v *= 12.92;
} else {
v = 1.055*Math.pow(v,1.0/exponent)-0.055;
}
return (v*255);
The formulas for calculating greyscale are as follows:
like PSApproximates 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 YIQYIQ 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 XYZred_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))
Lightness½ × (max(R,G,B) + min(R,G,B)), see Puzzling Greys.
Average(R + G + B) ÷ 3, see Puzzling Greys.
 

 
more experiments for the sake of my dreams