one fing leads . . .
 

Experiments with Colour Blotching
Re-colour an image according to different brightness criteria. Needs a bit of experiment with the sliders to get a satisfyingly artistic or *meaningful* result. The changed image is shown below the sliders. And the purpose of it all? I don’t know. Yet. It does help in the understanding of colour brightness levels.
Select picture
or specify image url apply
 will be converted to 800px × 600px – see copyright notice
 
 
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where the difference in brightness between RED element of a pixel and the next highest of the triad is greater than the brightness-diff slider value, pixel will become the red-replace colour
brightnesss diff:
red-replace hex:        
 
 
 
 
 
where the difference in brightness between GREEN element of a pixel and the next highest of the triad is greater than the brightness-diff slider value, pixel will become the green-replace colour
brightnesss diff:
green-replace hex:        
 
 
 
 
 
where the difference in brightness between BLUE element of a pixel and the next highest of the triad is greater than the brightness-diff slider value, pixel will become the blue-replace colour
brightnesss diff:
blue-replace hex:        
 
 
 
 
 
pixels will be black where they are not alredy converted and the brightness is <= the slider value>
 
pixels will be white where they are not already converted and the brightness is >= the slider value
 
grey-replace hex:        
all other pixels will become this shade of grey
 
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, 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);
}
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