OpenCV 4 with Python Blueprints - Second Edition

Extracting exposure strength from images

Assuming the principle of reciprocity for all the camera parameters that we discussed previously, let's try to come up with a function—exposure_strength—that returns a time equivalent to the exposure:

1. First, let's set a reference for ISO speed and f-stop:

def exposure_strength(path, iso_ref=100, f_stop_ref=6.375):

2. Then, let's use the exifread Python package, which makes it easy to read the metadata associated with the images. Most modern cameras record the metadata in this standard format:

    with open(path, 'rb') as infile:        tags = exifread.process_file(infile)

3. Then, let's extract the f_stop value and see how much bigger the entrance pupil area to the reference was:

 [f_stop] = tags['EXIF ApertureValue'].values ...