C# Crop white space from around the image

This code will crop the image based on all white and transparent pixels from around the image

public static Bitmap CropWhiteSpace(Bitmap bmp)
{
  int w = bmp.Width;
  int h = bmp.Height;
  int white = 0xffffff;
 
  Func allWhiteRow = r =>
  {
    for (int i = 0; i < w; ++i)
      if ((bmp.GetPixel(i, r).ToArgb() & white) != white)
        return false;
    return true;
  };
 
  Func allWhiteColumn = c =>
  {
    for (int i = 0; i < h; ++i)
      if ((bmp.GetPixel(c, i).ToArgb() & white) != white)
        return false;
    return true;
  };
 
  int topmost = 0;
  for (int row = 0; row < h; ++row)
  {
    if (!allWhiteRow(row))
      break;
    topmost = row;
  }
 
  int bottommost = 0;
  for (int row = h - 1; row >= 0; --row)
  {
    if (!allWhiteRow(row))
      break;
    bottommost = row;
  }
 
  int leftmost = 0, rightmost = 0;
  for (int col = 0; col < w; ++col)
  {
    if (!allWhiteColumn(col))
      break;
    leftmost = col;
  }
 
  for (int col = w - 1; col >= 0; --col)
  {
    if (!allWhiteColumn(col))
      break;
    rightmost = col;
  }
 
  if (rightmost == 0) rightmost = w; // As reached left
  if (bottommost == 0) bottommost = h; // As reached top.
 
  int croppedWidth = rightmost - leftmost;
  int croppedHeight = bottommost - topmost;
 
  if (croppedWidth == 0) // No border on left or right
  {
    leftmost = 0;
    croppedWidth = w;
  }
 
  if (croppedHeight == 0) // No border on top or bottom
  {
    topmost = 0;
    croppedHeight = h;
  }
 
  try
  {
    var target = new Bitmap(croppedWidth, croppedHeight);
    using (Graphics g = Graphics.FromImage(target))
    {
      g.DrawImage(bmp,
        new RectangleF(0, 0, croppedWidth, croppedHeight),
        new RectangleF(leftmost, topmost, croppedWidth, croppedHeight),
        GraphicsUnit.Pixel);
    }
    return target;
  }
  catch (Exception ex)
  {
    throw new Exception(
      string.Format("Values are topmost={0} btm={1} left={2} right={3} croppedWidth={4} croppedHeight={5}", topmost, bottommost, leftmost, rightmost, croppedWidth, croppedHeight),
      ex);
  }
}

To test code you can try this

[Test]
public void Test()
{
  var inputPath = "image.png";
  var outputPath = inputPath.Replace(".png", "-out.png");
 
  var bitmap = new Bitmap(inputPath);
  var cropped = CropWhiteSpace(bitmap);
  cropped.Save(outputPath, ImageFormat.Png); 
}

OR in ASP.net as

using (Bitmap bitmap = new Bitmap(pngpath))
{
 using (MemoryStream ms = new MemoryStream())
 {
  var cropped = CropWhiteSpace(bitmap);
  cropped.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
  ms.WriteTo(context.Response.OutputStream);
  //cropped.Save(outputPath, System.Drawing.Imaging.ImageFormat.Png); 

  //ms.WriteTo(context.Response.OutputStream);
 }
}