C # - Crop Transparent / White Space

Question

I am trying to remove all white or transparent pixels from an image, leaving the actual image (cropped). I tried several solutions but no one works. Any suggestions or am I going to spend the night using the cropping code?

Answer 1

public Bitmap CropBitmap(Bitmap original)
{
    // determine new left
    int newLeft = -1;
    for (int x = 0; x < original.Width; x++)
    {
        for (int y = 0; y < original.Height; y++)
        {
            Color color = original.GetPixel(x, y);
            if ((color.R != 255) || (color.G != 255) || (color.B != 255) || 
                (color.A != 0))
            {
                // this pixel is either not white or not fully transparent
                newLeft = x;
                break;
            }
        }
        if (newLeft != -1)
        {
            break;
        }

        // repeat logic for new right, top and bottom

    }

    Bitmap ret = new Bitmap(newRight - newLeft, newTop - newBottom);
    using (Graphics g = Graphics.FromImage(ret)
    {
        // copy from the original onto the new, using the new coordinates as
        // source coordinates for the original
        g.DrawImage(...);
    }

    return ret
}

Please note that this feature will be as slow as dirt. GetPixel()incredibly slow, and access to properties Widthand Heighta Bitmapinside the loop is also slow. LockBitswould be the right way to do this - here are some examples on StackOverflow.

Answer 2

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  // Load the bitmap
  Bitmap originalBitmap = Bitmap.FromFile("d:\\temp\\test.bmp") as Bitmap;

  // Find the min/max non-white/transparent pixels
  Point min = new Point(int.MaxValue, int.MaxValue);
  Point max = new Point(int.MinValue, int.MinValue);

  for (int x = 0; x < originalBitmap.Width; ++x)
  {
    for (int y = 0; y < originalBitmap.Height; ++y)
    {
      Color pixelColor = originalBitmap.GetPixel(x, y);
      if (!(pixelColor.R == 255 && pixelColor.G == 255 && pixelColor.B == 255)
        || pixelColor.A < 255)
      {
        if (x < min.X) min.X = x;
        if (y < min.Y) min.Y = y;

        if (x > max.X) max.X = x;
        if (y > max.Y) max.Y = y;
      }
    }
  }

  // Create a new bitmap from the crop rectangle
  Rectangle cropRectangle = new Rectangle(min.X, min.Y, max.X - min.X, max.Y - min.Y);
  Bitmap newBitmap = new Bitmap(cropRectangle.Width, cropRectangle.Height);
  using (Graphics g = Graphics.FromImage(newBitmap))
  {
    g.DrawImage(originalBitmap, 0, 0, cropRectangle, GraphicsUnit.Pixel);
  }

Answer 3

WPF WriteableBitmap. , ? , http://blogs.msdn.com/b/jgalasyn/archive/2008/04/17/using-writeablebitmap-to-display-a-procedural-texture.aspx

Answer 4

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Answer 5

I found a method for batch cropping several thousand .jpg files in 10 minutes, but I did not do this in the code. I used the Convert function of the Snag-It editor. I do not know if this is an option for you, if you need to do this pruning once, or your needs continue, but for the price of software that is not so much, I found this a worthy workaround. (I do not work or represent Techsmith.)

Joey