Hello all,

I am writing a program that uses a genetic algorithm to 'evolve' a randomly generated image in to a template image that I provide. Here is what it looks like:



Every generation it creates (by default) 150 copies with random mutations (ellipse color/shape), and then compares them all to the template picture to see which is most similar, and that one moves on to the next generation. The current method I use to compare them is a pixel by pixel Euclidean Distance measurement. This takes about 8-9 seconds to evaluate the 150 children. Which might not seem like much, but to get a decently evolved image it can take at least 40,000 generations (about 4 days at given speed). This is too slow to test the results of different mutation rate / children / etc combinations.

What faster methods of comparing the two images are there? Or what other ideas do you have to make this more efficient?
My only thought so far is to reduce the dimensions of the images but that takes the fun out of creating a high quality replica ;)

Sounds like you have either implemented the distance calculation incorrectly or you have a really slow computer. A very naive test in Matlab at full 80-bit floating point precision and 500x500 images (just making some estimate of the size from your screen shot) images takes roughly a millisecond per image pair, and that time includes a few memory allocations for temporary buffers as well. Can you show how you're calculating the distance?

I was going to move in to making it work for color images eventually, but I figured to start with greyscale cause it should be faster. Thanks for the tip about color images though.

Kinda expected it to go faster myself, so I wouldn't be surprised if something's wrong. Here's my function for it (C#):
private double GetEuclideanDistance(Image img1, Image img2)
{
int dist = 0.0;
try
{
Bitmap a = new Bitmap(img1);
Bitmap b = new Bitmap(img2);
if (a.Width != b.Width || a.Height != b.Height)
{
System.Windows.Forms.MessageBox.Show("Target comparable image does not have the same dimensions. Cannot get Euclidean Distance.");
return 0;
}
int nRows = a.Height;
int nCols = a.Width;
for (int row = 0; row < nRows; row++)
{
for (int col = 0; col < nCols; col++)
{
int d = a.GetPixel(col, row).ToArgb() - b.GetPixel(col, row).ToArgb();
dist += (d * d);
}
}
}
catch (Exception ex)
{
IEvo.ReportException(ex, "GetEuclideanDistance");
}
return Math.Sqrt(dist);
}

My timings show that it takes around 400ms to complete every time. Only about 15 ms for it to copy the images in to Bitmaps.

GetPixel is probably very slow. Individually locking the image for each pixel.
If this was C++, I'd tell you to lock the whole image, and process it with a pointer for processing times close to that of a copy.
Conversion to argb should also be unneccessary for grayscale, and a bit expensive. (compared to just add's to step the pointer, and a sub to compare raw pixels directly)
You probably can do something like that in C# too, hopefully someone else can tell you how.

Wow, yes apparently GetPixel is incredibly slow. I don't understand the idea behind image locking, but I found this post that explains how to get access to the bitmaps byte array.

http://stackoverflow.com/questions/1563038/fast-work-with-bitmaps-in-c-sharp

That cut the algorithms time down to 11 ms using the Marshal'ing method. To subtract the RGB values from each other just (aR+aG+aB)-(bR+bG+bB)?

Thanks to everyone (especially Spiro for the continued support!) your answers have been very helpful! I've learned some very important things here