How it works...

To save an image, you should use the cv2.imwrite function. The file's format is determined by this function, as can be seen in the filename (JPEG, PNG, and some others are supported). There are two main options for saving images: whether to lose some information while saving, or not. 

The cv2.imwrite function takes three arguments: the path of output file, the image itself, and the parameters of saving. When saving an image to PNG format, we can specify the compression level. The value of IMWRITE_PNG_COMPRESSION must be in the (0, 9) interval—the bigger the number, the smaller the file on the disk, but the slower the decoding process.

When saving to JPEG format, we can manage the compression process by setting the value of IMWRITE_JPEG_QUALITY. We can set this as any value from 0 to 100. But here, we have a situation where bigger is better. Larger values lead to higher result quality and a lower amount of JPEG artifacts.