从图像中的每个像素获取色相

Question

I am trying to get the Hue or 'H' of every pixel of an image, then changing the colour of the pixel that has a specific Hue. I am trying to change all pixels that have a hue >= 210 and <=260, which is the different hues of blue.

Here is my code:

// 'i' is the image
// 'b' is the bitmap of the image
float y;
for (int a = 0; a < i.Height; a++) 
{ 
    for (int c = 0; c < i.Width; c++) 
    { 
        y = b.GetPixel(c, a).GetHue(); 
        if (y >= 210 && y <= 260) 
            { 
                b.SetPixel(c, a, Color.Black); 
            } 
    } 
}

The only problem is that it doesn't pickup any blue colours, which are from 210 - 260. I am pretty sure that I am doing this correctly, but I must not be since it isnt working.

Please post here if you can solve this problem, Thanks!

Edit: I put a breakpoint on SetPixel, and it gets called many, many times so now I will check if I am saving the picture right.

Edit 2: I figured it out! I wasn't saving the picture.

Answer 1

Use, LockBits method, Luke!

Or, i think, it`s better be done with Graphics context.

Answer 2

It kind of worked for me. In the code below I have a Windows Form with PictureBox called imgViwer. Then clicking the a button I execute the code:

private void HueFilter()
{
  float y;
  Bitmap i = (Bitmap)imgViwer.Image;

  for (int a = 0; a < i.Height; a++)
  {
      for (int c = 0; c < i.Width; c++)
      {                   
          y = i.GetPixel(c, a).GetHue();
          if (y >= 210 && y <= 260)
          {
              i.SetPixel(c, a, Color.Black);
          }
      }
  }

  imgViwer.Image = i;
}

In your case you have an output image called b that should be assigned back to the PictureBox to the refresh.