Remove surrounding whitespace from an image

Question

I have a block of product images we received from a customer. Each product image is a picture of something and it was taken with a white background. I would like to crop all the surrounding parts of the image but leave only the product in the middle. Is this possible?

As an example: http://www.5dnet.de/media/catalog/product/d/r/dress_shoes_5.jpg

I don't want all white pixels removed, however I do want the image cropped so that the top-most row of pixels contains one non-white pixel, the left-most vertical row of pixels contains one non-white pixel, bottom-most horizontal row of pixels contains one non-white pixel, etc.

Code in C# or VB.net would be appreciated.

Thanks, Kyle

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Edit: If anyone would like source code for this, I have posted my solution online here: http://fitnessconnections.com/blog/remove-surrounding-white-space-from-an-image/

Answer 1

I've written code to do this myself - it's not too difficult to get the basics going.

Essentially, you need to scan pixel rows/columns to check for non-white pixels and isolate the bounds of the product image, then create a new bitmap with just that region.

Note that while the Bitmap.GetPixel() method works, it's relatively slow. If processing time is important, you'll need to use Bitmap.LockBits() to lock the bitmap in memory, and then some simple pointer use inside an unsafe { } block to access the pixels directly.

This article on CodeProject gives some more details that you'll probably find useful.

Answer 2

It's certainly possible. In pseudocode:

topmost = 0
for row from 0 to numRows:
    if allWhiteRow(row): topmost = row
botmost = 0
  for row from numRows-1 to 0:
    if allWhiteRow(row): botmost = row

And similarly for left and right.

The code for allWhiteRow would involve looking at the pixels in that row and making sure they're all close to 255,255,255.

Answer 3

The pnmcrop utility from the netpbm graphics utilities library does exactly that.

I suggest looking at their code, available from http://netpbm.sourceforge.net/

Answer 4

Here's my (rather lengthy) solution:

public Bitmap Crop(Bitmap bmp)
{
  int w = bmp.Width, h = bmp.Height;

  Func<int, bool> allWhiteRow = row =>
  {
    for (int i = 0; i < w; ++i)
      if (bmp.GetPixel(i, row).R != 255)
        return false;
    return true;
  };

  Func<int, bool> allWhiteColumn = col =>
  {
    for (int i = 0; i < h; ++i)
      if (bmp.GetPixel(col, i).R != 255)
        return false;
    return true;
  };

  int topmost = 0;
  for (int row = 0; row < h; ++row)
  {
    if (allWhiteRow(row))
      topmost = row;
    else break;
  }

  int bottommost = 0;
  for (int row = h - 1; row >= 0; --row)
  {
    if (allWhiteRow(row))
      bottommost = row;
    else break;
  }

  int leftmost = 0, rightmost = 0;
  for (int col = 0; col < w; ++col)
  {
    if (allWhiteColumn(col))
      leftmost = col;
    else
      break;
  }

  for (int col = w-1; col >= 0; --col)
  {
    if (allWhiteColumn(col))
      rightmost = col;
    else
      break;
  }

  int croppedWidth = rightmost - leftmost;
  int croppedHeight = bottommost - topmost;
  try
  {
    Bitmap 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}", topmost, bottommost, leftmost, rightmost),
      ex);
  }
}