Recently, I have been using the function Haartraining provided by Opencv to train the classifier. The previous picture used was 20*20, which could train the classifier. Later, when it was changed to 80*86, the error was reported, which was due to insufficient memory. Here is a screenshot of the error report:

So, I looked it up on the Internet and found a solution: change the debugging platform from 32 to 64, because there seems to be a problem with 32 bits, no matter how big your actual memory is, it only works around 2 or 3 gs. Another solution is to make your training pictures smaller.