title: How to crop image based on binary mask
body: <p>I am using torch with some semantic segmentation algorithms to produce a binary mask of the segmented images. I would then like to crop the images based on that mask. To be clear I need to crop it on a per pixel basis. It seems like a simple problem but the only solution I can conjure up is to either invert a <code>draw mask</code> function like in the Coco API, or iterate over each pixel in the array and mask together setting the pixel to black if not needed. I feel like there is a better way of doing this. Libraries in Lua, Python, Go, or C++ will work for me. Any ideas?</p>