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PORecognizing image within image in C#
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copied!<p>I'd like to find an image (<em>needle</em>) within an image (<em>haystack</em>).</p> <p>To keep things simple I take two screenshots of my desktop. One full size (<em>haystack</em>) and a tiny one (<em>needle</em>). I then loop through the haystack image and try to find the needle image.</p> <ol> <li>capture needle and haystack screenshot</li> <li>loop through haystack, looking out for haystack[i] == first pixel of needle</li> <li>[if 2. is true:] loop through the 2nd to last pixel of needle and compare it to haystack[i]</li> </ol> <p>Expected result: the needle image is found at the correct location.</p> <p>I already got it working for some coordinates/widths/heights (A).</p> <p>But sometimes bits seem to be "off" and therefore <strong>no match is found</strong> (B).</p> <p>What could I be doing wrong? Any suggestions are welcome. Thanks.</p> <hr> <pre><code>var needle_height = 25; var needle_width = 25; var haystack_height = 400; var haystack_width = 500; </code></pre> <hr> <p><strong>A. example input - match</strong></p> <pre><code>var needle = screenshot(5, 3, needle_width, needle_height); var haystack = screenshot(0, 0, haystack_width, haystack_height); var result = findmatch(haystack, needle); </code></pre> <p><strong>B. example input - NO match</strong></p> <pre><code>var needle = screenshot(5, 5, needle_width, needle_height); var haystack = screenshot(0, 0, haystack_width, haystack_height); var result = findmatch(haystack, needle); </code></pre> <hr> <p><strong>1. capture needle and haystack image</strong></p> <pre><code>private int[] screenshot(int x, int y, int width, int height) { Bitmap bmp = new Bitmap(width, height, PixelFormat.Format32bppArgb); Graphics.FromImage(bmp).CopyFromScreen(x, y, 0, 0, bmp.Size); var bmd = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadOnly, bmp.PixelFormat); var ptr = bmd.Scan0; var bytes = bmd.Stride * bmp.Height / 4; var result = new int[bytes]; Marshal.Copy(ptr, result, 0, bytes); bmp.UnlockBits(bmd); return result; } </code></pre> <p><strong>2. try to find a match</strong></p> <pre><code>public Point findmatch(int[] haystack, int[] needle) { var firstpixel = needle[0]; for (int i = 0; i < haystack.Length; i++) { if (haystack[i] == firstpixel) { var y = i / haystack_height; var x = i % haystack_width; var matched = checkmatch(haystack, needle, x, y); if (matched) return (new Point(x,y)); } } return new Point(); } </code></pre> <p><strong>3. verify full match</strong> </p> <pre><code>public bool checkmatch(int[] haystack, int[] needle, int startx, int starty) { for (int y = starty; y < starty + needle_height; y++) { for (int x = startx; x < startx + needle_width; x++) { int haystack_index = y * haystack_width + x; int needle_index = (y - starty) * needle_width + x - startx; if (haystack[haystack_index] != needle[needle_index]) return false; } } return true; } </code></pre>

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