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    <p>I've modified <code>GetOutlinePoints</code> by adding a helper variable than verifies the position at which new points should be added. </p> <p>The idea of the outline detection algorithm in your code is something like looking at the image while standing each of its edges and writing down all non-transparent pixels that are visible. It's ok, however, you always added pixels to the end of the collection, which caused issues. I've added a variable that remembers position of the last pixel visible from the previous edge and the current one and uses it to determine index where the new pixel should be added. I suppose it should work as long as the outline is continuous, but I suppose it is in your case.</p> <p>I've tested it on several images and it seems to work correctly:</p> <pre><code>public static Point[] GetOutlinePoints(Bitmap image) { List&lt;Point&gt; outlinePoints = new List&lt;Point&gt;(); BitmapData bitmapData = image.LockBits(new Rectangle(0, 0, image.Width, image.Height), ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb); byte[] originalBytes = new byte[image.Width * image.Height * 4]; Marshal.Copy(bitmapData.Scan0, originalBytes, 0, originalBytes.Length); //find non-transparent pixels visible from the top of the image for (int x = 0; x &lt; bitmapData.Width; x++) { for (int y = 0; y &lt; bitmapData.Height; y++) { byte alpha = originalBytes[y * bitmapData.Stride + 4 * x + 3]; if (alpha != 0) { Point p = new Point(x, y); if (!ContainsPoint(outlinePoints, p)) outlinePoints.Add(p); break; } } } //helper variable for storing position of the last pixel visible from both sides //or last inserted pixel int? lastInsertedPosition = null; //find non-transparent pixels visible from the right side of the image for (int y = 0; y &lt; bitmapData.Height; y++) { for (int x = bitmapData.Width - 1; x &gt;= 0; x--) { byte alpha = originalBytes[y * bitmapData.Stride + 4 * x + 3]; if (alpha != 0) { Point p = new Point(x, y); if (!ContainsPoint(outlinePoints, p)) { if (lastInsertedPosition.HasValue) { outlinePoints.Insert(lastInsertedPosition.Value + 1, p); lastInsertedPosition += 1; } else { outlinePoints.Add(p); } } else { //save last common pixel from visible from more than one sides lastInsertedPosition = outlinePoints.IndexOf(p); } break; } } } lastInsertedPosition = null; //find non-transparent pixels visible from the bottom of the image for (int x = bitmapData.Width - 1; x &gt;= 0; x--) { for (int y = bitmapData.Height - 1; y &gt;= 0; y--) { byte alpha = originalBytes[y * bitmapData.Stride + 4 * x + 3]; if (alpha != 0) { Point p = new Point(x, y); if (!ContainsPoint(outlinePoints, p)) { if (lastInsertedPosition.HasValue) { outlinePoints.Insert(lastInsertedPosition.Value + 1, p); lastInsertedPosition += 1; } else { outlinePoints.Add(p); } } else { //save last common pixel from visible from more than one sides lastInsertedPosition = outlinePoints.IndexOf(p); } break; } } } lastInsertedPosition = null; //find non-transparent pixels visible from the left side of the image for (int y = bitmapData.Height - 1; y &gt;= 0; y--) { for (int x = 0; x &lt; bitmapData.Width; x++) { byte alpha = originalBytes[y * bitmapData.Stride + 4 * x + 3]; if (alpha != 0) { Point p = new Point(x, y); if (!ContainsPoint(outlinePoints, p)) { if (lastInsertedPosition.HasValue) { outlinePoints.Insert(lastInsertedPosition.Value + 1, p); lastInsertedPosition += 1; } else { outlinePoints.Add(p); } } else { //save last common pixel from visible from more than one sides lastInsertedPosition = outlinePoints.IndexOf(p); } break; } } } // Added to close the loop outlinePoints.Add(outlinePoints[0]); image.UnlockBits(bitmapData); return outlinePoints.ToArray(); } </code></pre> <p><strong>Update:</strong> This algorithm won't work correctly for images that have outline parts not "visible" from any of the edges. See comments for suggested solutions. I'll try to post a code snippet later.</p> <p><strong>Update II</strong></p> <p>I've prepared another algorithm as described in my comments. It just crawls around the object and saves the outline. </p> <p>First, it finds the first pixel of the outline using a method from the previous algorithm. Then, it looks throught the neighbouring pixels in clockwise order, find the first one that is transparent and then continues browsing, but looking for a non-transparent one. The first non-transparent pixel found is the next one in the outline. The loop continues until it goes around the whole object and gets back to the starting pixel.</p> <pre><code>public static Point[] GetOutlinePointsNEW(Bitmap image) { List&lt;Point&gt; outlinePoints = new List&lt;Point&gt;(); BitmapData bitmapData = image.LockBits(new Rectangle(0, 0, image.Width, image.Height), ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb); Point currentP = new Point(0, 0); Point firstP = new Point(0, 0); byte[] originalBytes = new byte[image.Width * image.Height * 4]; Marshal.Copy(bitmapData.Scan0, originalBytes, 0, originalBytes.Length); //find non-transparent pixels visible from the top of the image for (int x = 0; x &lt; bitmapData.Width &amp;&amp; outlinePoints.Count == 0; x++) { for (int y = 0; y &lt; bitmapData.Height &amp;&amp; outlinePoints.Count == 0; y++) { byte alpha = originalBytes[y * bitmapData.Stride + 4 * x + 3]; if (alpha != 0) { Point p = new Point(x, y); outlinePoints.Add(p); currentP = p; firstP = p; break; } } } Point[] neighbourPoints = new Point[] { new Point(-1, -1), new Point(0, -1), new Point(1, -1), new Point(1, 0), new Point(1, 1), new Point(0, 1), new Point(-1, 1), new Point(-1, 0) }; //crawl around the object and look for the next pixel of the outline do { bool transparentNeighbourFound = false; bool nextPixelFound = false; int i; //searching is done in clockwise order for (i = 0; (i &lt; neighbourPoints.Length * 2) &amp;&amp; !nextPixelFound; ++i) { int neighbourPosition = i % neighbourPoints.Length; int x = currentP.X + neighbourPoints[neighbourPosition].X; int y = currentP.Y + neighbourPoints[neighbourPosition].Y; byte alpha = originalBytes[y * bitmapData.Stride + 4 * x + 3]; //a transparent pixel has to be found first if (!transparentNeighbourFound) { if (alpha == 0) { transparentNeighbourFound = true; } } else //after a transparent pixel is found, a next non-transparent one is the next pixel of the outline { if (alpha != 0) { Point p = new Point(x, y); currentP = p; outlinePoints.Add(p); nextPixelFound = true; } } } } while (currentP != firstP); image.UnlockBits(bitmapData); return outlinePoints.ToArray(); } </code></pre> <p>One thing to remember is that it does work IF object does NOT ends at the edge of the image (there has to be a transparent space between the object and each of the edges). </p> <p>This can be easily done if you just make the image one line larger at each side before passing it to the <code>GetOutlinePointsNEW</code> method.</p>
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    1. POCreating a GraphicsPath from a semi-transparent bitmap
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    1. USLukasz M
    1. USLukasz M
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    1. COYes this seems to work perfectly with all of my 50 or so images.
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      1. USTrevor Elliott
    2. COYou hit the nail on the head with that. I knew I had to insert those odd points but I had no idea how to calculate where. I have to wait 22 hours to award your bounty.
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      1. USTrevor Elliott
    3. COI'm glad it helped :). I'll look more into this code later, because I think I'm not sure if it works correctly in some special cases. I'll investigate this later. Also, let me know if you find any bug in this code.
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      1. USLukasz M
 

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