percent to Argb color value

Question

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How to find Gray color percentage from ARGB value?

Actually I want to set color according to Gray color percentage in an image.

I wrote following code but it is not working so I thought if I get percentage of colour then it could be better option.

C#

Color compareClr = Color.FromArgb(75, 75, 75);
Color compareClr2 = Color.FromArgb(90, 90, 90);
Color compareClr3 = Color.FromArgb(105, 105, 105);
Color compareClr4 = Color.FromArgb(150, 150, 150);
for (int y = 0; y < lockBitmap.Height; y++)
{
    for (int x = 0; x < lockBitmap.Width; x++)
    {
        double d= Color.LightGray.GetHue();
        Console.WriteLine("GetHue " + d);
        //Console.WriteLine((System.Drawing.Color.LightGray.ToArgb() == lockBitmap.GetPixel(x, y).ToArgb()) + " LightGray");
        //Console.WriteLine((System.Drawing.Color.Gray.ToArgb() == lockBitmap.GetPixel(x, y).ToArgb()) + " Gray");
        //Console.WriteLine((System.Drawing.Color.DarkGray.ToArgb() == lockBitmap.GetPixel(x, y).ToArgb()) + " DarkGray");
        if (lockBitmap.GetPixel(x, y).ToArgb() == compareClr.ToArgb())
            lockBitmap.SetPixel(x, y, Color.Cyan);
        else if (lockBitmap.GetPixel(x, y).ToArgb() == compareClr2.ToArgb())
            lockBitmap.SetPixel(x, y, Color.Green);
        else if (lockBitmap.GetPixel(x, y).ToArgb() == compareClr3.ToArgb())
            lockBitmap.SetPixel(x, y, Color.Yellow);
        else
            lockBitmap.SetPixel(x, y, Color.Blue);
    }
}

Posted 19-Mar-13 1:59am

rajesh@1989

Updated 19-Mar-13 2:06am

Prasad Khandekar

v3

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Comments

CPallini 19-Mar-13 10:42am

"Actually I want to set color according to Gray color percentage in an image."
What do you mean, exactly?

2 solutions

Solution 1

The FromArgb methods assume 32-bits-per-pixel pixel format (only), 8 bits per each color component and A (opacity).
It means that the maximum color component value is byte.MaximumValue == 0xFF == 255, which corresponds to 100%. And minimum value is 0, corresponds to 0%. Can do the math?

—SA

Posted 19-Mar-13 4:21am

Sergey Alexandrovich Kryukov

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Steve44 · Accepted Answer · 2013-03-19T12:16:00

From your description I would assume you want to calculate the luminance of a pixel and depending in which range it is set an overlay color.

C#

for (int y = 0; y < lockBitmap.Height; y++)
{
   for (int x = 0; x < lockBitmap.Width; x++)
   {
      // get the color of the pixel
      Color pix = lockBitmap.GetPixel(x, y);
      // calculate luminance from the components
      // result will be in the range [0.0, 255.0]
      double lum = (double)pix.R*0.3+(double)pix.G*0.59+(double)pix.B*0.11;
      // color according to the luminance ranges
      if(lum < 75.0) {
        lockBitmap.SetPixel(x, y, Color.Cyan);
      } else if (lum < 90.0) {
        lockBitmap.SetPixel(x, y, Color.Green);
      } else if (lum < 105.0) {
        lockBitmap.SetPixel(x, y, Color.Yellow);
      } else {
        lockBitmap.SetPixel(x, y, Color.Blue);
      }
   }
}