Good features to compare an image with a capture of this image

Question

I want to capture one frame with all the frames stored in a database. This frame is captured by the mobile phone, while the database is with the original ones. I have been searching most days in order to find a good method to compare them, taking into account that they have not the same resolution, colors and luminance, etc. Does anyone have an idea?

I have already done the preprocessing step of the captured frame to be as faithful as possible than the original one with C++ and the OpenCV library. But then, I do not know what can be a good feature to compare them or not.

Any comment will be very helpful, thank you!

EDIT: I implemented an algorithm which compares the difference between the two images resized to 160x90, in grayscale and quantized. The results are the following:

The mean value of the image difference is 13. However, if I use two completely different images, the mean value of the image difference is 20. So, I do not know if this measure can be improved on some manner in order to have a better margin for the matching.

Thanks for the help in advance.

Answer 1

Cut the color depth from 24-bits per pixel (or whatever) to 8 or 16 bits per pixel. You may be able use a posterize function for this. Then resize both images to a small size (maybe 16x16 or 100x100, depending on your images), and then compare. This should match similar images fairly closely. It will not take into account different rotation and locations of objects in the image.