Removing R from RGB Color - image-processing

Question

Is there a way to remove the red channel of an RGB pixel in a way such that in the resulting picture the red color goes to white not to black? I need to distinguish between red color and blue/black color, but in different light the RGB value varies. If I simply remove the R channel, darker red colors become black and I want the opposite result.
Thanks!

Answer 1

If I understand you correctly -
You need to normalize the red channel value and then use it as a mixing value:
mix = R / 255
Then mix white with the normal color minus the red channel using the mix factor:
Original-red White
R' = 0 + 255 * mix
G' = G * (1 - mix) + 255 * mix
B' = B * (1 - mix) + 255 * mix
Just notice it will kill the yellow and magenta colors as well as these of course uses the red channel, and the more red the more white is mixed in.
You should be able to get around this using the CMYK color-model, or a combination of both, so you can separate out all the main components. Then override the mix with f.ex. the yellow/magenta components from CMYK.
The mixing process should be the same as described though.
Conceptual demo
var ctx = c.getContext("2d");
var img = new Image;
img.onload = function() {
c.width = img.width;
c.height = img.height;
ctx.drawImage(this, 0, 0);
var idata = ctx.getImageData(0,0,c.width,c.height),
data = idata.data, len = data.length, i, mix;
/* mix = R / 255
R = 0 + 255 * mix
G = G * (1 - mix) + 255 * mix
B = B * (1 - mix) + 255 * mix
*/
for(i = 0; i < len; i+= 4) {
mix = data[i] / 255; // mix using red
data[i ] = 255 * mix; // red channel
data[i+1] = data[i+1] * (1 - mix) + 255 * mix; // green channel
data[i+2] = data[i+2] * (1 - mix) + 255 * mix; // blue channel
}
ctx.putImageData(idata,0,0);
};
img.crossOrigin = "";
img.src = "//i.imgur.com/ptOPQZx.png";
document.body.appendChild(img)
<h4>Red removed + to white</h4><canvas id=c></canvas><h4>Original:</h4>