Probably best way is one of the above (Image::Magick or gimp), but as mentioned by rduke15, you have to go through pixels, but not all of them. I actualy did this recently, but in a C# program. The code is below if it helps at all as pseudocode. It takes a couple shortcuts in the loop bounds to try to check the minimum number of pixels. 
            Bitmap canvas = new Bitmap("C:\\WINNT\\BgInfo.bmp");
            Color bgcolor = canvas.GetPixel(5,5);
            
            int left = 0;
            for(int x=0; x< canvas.Width; x++){
                for(int y=0; y< canvas.Height; y++){
                    if( canvas.GetPixel(x,y) != bgcolor ){
                        left = x;
                        break;
                    }
                }
                if( left > 0 ){
                    break;
                }
            }
            int top = 0;
            for(int y=0; y< canvas.Height; y++){
                for(int x=left; x< canvas.Width; x++){
                    if( canvas.GetPixel(x,y) != bgcolor ){
                        top = y;
                        break;
                    }
                }
                if( top > 0 ){
                    break;
                }
            }

            int right = 0;
            for(int x = canvas.Width-1; x>=left; x--){
                for(int y = canvas.Height-1; y>=top; y--){
                    if( canvas.GetPixel(x,y) != bgcolor ){
                        right = x;
                        break;
                    }
                }
                if( right > 0 ){
                    break;
                }
            }
            int bottom = 0;
            for(int y = canvas.Height-1; y>=top; y--){
                for(int x = right; x>=left; x--){
                    if( canvas.GetPixel(x,y) != bgcolor ){
                        bottom = y;
                        break;
                    }
                }
                if( bottom > 0 ){
                    break;
                }
            }
            int pad = 10;
            left -= pad;
            top -= pad;
            right += pad;
            bottom += pad;
            if( top>0 && left>0 && right>0 && bottom>0 && right > left
+ && bottom > top ){
                Rectangle r = new Rectangle(left, top, right-left, bot
+tom-top);
                Bitmap cropped = canvas.Clone(r, canvas.PixelFormat);
                canvas.Dispose();
                return cropped;
            }

[download]

In reply to Re: Cropping dependant on image contents by davidrw
in thread Cropping dependant on image contents by matthewsnape

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