custom image size using the esp32-camera library in platformio

Question

I've been trying to write a program that processes image data from an esp32-cam, but in order to process it on the device, I cannot use the jpeg format to store data, but rather have to use GRAYSCALE, which limits me to a very slow frame rate. Long story short, I only need a thin, predefined sliver of the photo, and was hoping I could create a custom image format to only get that portion of the photo to speed up processing time. I'm fairly new to c++ and as such do not want to screw anything up with the packages functions; Does anyone know how one could create a custom image format in the sp32-camera library in the esp-idf framework that only takes a small portion of the camera's data?