RGB values for grayscale in 24-bit

anurag4u · 12-11-2012, 05:57 AM

Hi,
Please see the code below.

Code:

for (i=0; i<= 255; i++)
  {
    sprintf(spec, "rgb:%02x/%02x/%02x", i, i, i);

    if(XParseColor(display, default_cmap, spec, &color))
    {
        XAllocColor(display, default_cmap, &color);
    }
}

then I am printing color.red, color.blue and color.green values. These values range from 0 to 65535.

If I understand it correctly, Each color (R, G, B) has 8-bits each, so values should range from 0 to 255.

Please help me understand why the values are 256 times the expected values.

steelneck · 12-11-2012, 08:30 AM

Because you have an RGB image, not a single channel BW. An RGB image in 24-bit will have a range of 0 to 65535 for each channel, and if that image look BW, it is only desaturated.

anurag4u · 12-12-2012, 11:12 PM

Thanks for the explanation.