I want to crop a photo that I will want to enlarge after post processing. What do I need to do to keep a high enough resolution after cropping in order to enlarge the photo and still maintain a high resolution?
If you crop a photo, you will lose resolution by definition. But there are some promising new programs and algorithms out there, that can upscale a image to higher resolutions. BUT: there will never pop up new details, like some criminal investigations tv series show. If a detail in the photo is not good visible, it will also be not good visible in an upscaled photo.
Resolution is defined in terms of pixel count. When you crop the image, naturally you lose pixels. So when you resize the photo, the photo becomes less low resolution. If you use a high resolution camera (like 24MP, 36 MP or above) the crop might be ok. But it is not clear how big you want to enlarge.