summing red() green() and blue() values

Programming Questions

magriffin

summing red() green() and blue() values

in Programming Questions • 2 months ago

hi there,

i have been working on a pixel averaging project, and have two ways of generating an average that to my eyes seem equivalent, but have not been producing equivalent results. i think i've been staring at it for far too long, so if anyone can see the reason, i'd be extremely grateful.

thanks!

method 1:

r = (red(pc0) + red(pc1) + red(pc2) + red(pc3) + red(pc4)) / 5;

g = (green(pc0) + green(pc1) + green(pc2) + green(pc3) + green(pc4)) / 5;

b = (blue(pc0) + blue(pc1) + blue(pc2) + blue(pc3) + blue(pc4)) / 5;

method 2:

r = r + red(pc0);

r = r + red(pc1);

r = r + red(pc2);

r = r + red(pc3);

r = r + red(pc4);

g = g + green(pc0);

g = g + green(pc1);

g = g + green(pc2);

g = g + green(pc3);

g = g + green(pc4);

b = b + blue(pc0);

b = b + blue(pc1);

b = b + blue(pc2);

b = b + blue(pc3);

b = b + blue(pc4);

r = r / 5;

g = g / 5;

b = b / 5;

note: the general version of this, using arrays, produces a result equivalent to method 2.

Replies(5)

quarks

Re: summing red() green() and blue() values

2 months ago

To get the same output change method 2 to

r = red(pc0);

r = r + red(pc1);

r = r + red(pc2);

r = r + red(pc3);

r = r + red(pc4);

g = green(pc0);

g = g + green(pc1);

g = g + green(pc2);

g = g + green(pc3);

g = g + green(pc4);

b = blue(pc0);

b = b + blue(pc1);

b = b + blue(pc2);

b = b + blue(pc3);

b = b + blue(pc4);

r = r / 5;

g = g / 5;

b = b / 5;

magriffin

Re: summing red() green() and blue() values

2 months ago

that worked, thanks. however, with an array, using the following method:

for(int l = 0; l < numimgs; l++){

pix[l] = pxlavg[l].get(i, j);

r += red(pix[l]);

g += green(pix[l]);

b += blue(pix[l]);

}

r = r / numimgs;

g = g / numimgs;

b = b / numimgs;

i get the same result as the original method 2.

quarks

Re: summing red() green() and blue() values

2 months ago

The problem with your original method 2 was that the variables r, g and b were not being initialised. The same is happening in your code with arrays. This code will initialise them to zero before we start counting.

r = g = b = 0;
for (int l = 0; l < numimgs; l++) {
pix[l] = pxlavg[l].get(i, j);

r += red(pix[l]);
g += green(pix[l]);
b += blue(pix[l]);
}

r = r / numimgs;
g = g / numimgs;
b = b / numimgs;

GoToLoop

Re: summing red() green() and blue() values

2 months ago

What about zeroing them before starting that loop?

r = g = b = 0;

Oh. quarks has replied already!

At least, here's a faster version:

r = g = b = 0;

for (int l = 0; l != NUM_IMGS; l++) {
  final color c = pix[l] = pxlAvg[l].get(i, j);

  r += c >> 020 & 0xFF;
  g += c >> 010 & 0xFF;
  b += c & 0xFF;
} 

r /= NUM_IMGS;
g /= NUM_IMGS;
b /= NUM_IMGS;

magriffin

Re: summing red() green() and blue() values

2 months ago

duh! thanks so much. i'd initialised them to 0 above in the code, but definitely the wrong place.

props to you both.

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