error in gray scale or B/W detection

[hvanstappen]

(tested with http://localhost:8000/ui/color) With the Blip-vqa-base method, the Warning messages for black&white or grayscale images seem wrong:

• color image: warning "image is in b/w or grayscale"
• color image with very low saturation: warning (OK)
• grayscale image: no warning
• bitonal image: warning (OK)

Although it seems the internal method uses the same function, in this case the gray scale or B/W detection seems to be correct

[TomDeneire]

The difference is in the fact that with internal labeling the image is resized in the function determine_image, whereas with blip this does not occur. I don't see why that should matter to the is_quasi_monochrome_with_rgb function (specifically the values for r.getextrema() == g.getextrema() == b.getextrema() are different), but will investigate further.

[TomDeneire]

https://github.com/datable-be/AI4C_ContentAnalysis/commit/6cd6afdb3cffba75fc2e898e92deff452b84ba73

Implemented new algorithm to detect black-and-white and/or grayscale images. Also included test corpus of 13 images which are all detected correctly by the algorithm.