如何优化图像比较脚本的性能？

I wrote a script that compares a huge set of images (more than 4500 files) against each other using a root mean square comparison. At first it resizes each image to 800x600 and takes a histogram. After that it builds an array of combinations and distributes them evenly to four threads which calculate the root mean square of every combination. Images with a RMS below 500 will be moved into folders to be manually sorted out later.I wrote a script that compares a huge set of im