The dictionary method will get slower for samples with a large number of overlapping points, so at some point switching back to iterating over all pixels becomes faster. Switching between the two methods based on pixel distribution would provide optimal performance

Just wanted to shoot you an optimization to your algorithm. On a 1024×1024 bitmap with 24 sampling points, speed increase is several orders of magnitude (1.8 sec down to 0.03 sec)

(a) Use a Dictionary to store the pixel intensity values.

(b) Use AddRange() to add the dictionary values to the sort list

(c) Use an empty, transparent bitmap sized like the target image instead of passing the target image through.

(d) Cut all opacity and GetPixel calls.
Instead, take the output image of the function (now a transparent bmp with the heat texture applied) and Draw it onto the area map image using DrawImage and and Image Attribute with a color matrix set

ColorMatrix cm = new ColorMatrix {Matrix33 = PointColorAlpha };

imageAttribute.SetColorMatrix(cm);

gTarget.DrawImage(m_LayerCache,
new Rectangle(0, 0, size.Width, size.Height), 0, 0, m_LayerCache.Width,
m_LayerCache.Height, GraphicsUnit.Pixel, m_textureAttributes);

(e) If opacity == 1, use DrawImageUnscaled instead, which is also several orders of magnitude faster than DrawImage

(f) If you want more speed and want to make the assumption that there is at least one pixel of zero intensity, only add pixels with >0 intensity to the dictionary and fix the min intensity at 0. That will shave another 10-20% of the rendering times.

Feel free to link! As I said, there’s no sense in reinventing the wheel more than a few times

Percentile mapping is the way to go – I ran into the same problem, e.g. writing the code from scratch, and ended up with a similar solution.

I’m using an indexed bitmap to map color to weight on the map, which has the benefit of being able to swap that bitmap out for different color schemes – which is useful when rendering on top of in-game minimap images of different color.

Mind if I link your article?

– Georg