About TODO Blog RSS Old blog Projects Gallery Notes

Fri, 11 May 2007

Solving captcha problems. Scaling.


I've added scaling into my algo of detecting matched images and changed part which detects how similar images are - now I use simple cover algo, i.e. the smaller amount of uncovered by tested letter pixels of the unknown symbol are, the better letter is being checked, this can lead to situations when black square will have the best match, but older algo (sum of the shortest distances between pixels of the tested image and database letter) is bad too - it fails when database letter crosses studied symbol in many places, so sum of distances becomes extremely small.
For example this quite complex test has been passed successfully:



But things are not too good for other a bit rotated cases. Since main symbol's axis does not match for database symbol (where it is vertical in standard font) and sudied symbol (where is can be arbitrary), amount of covered symbols does not represent matching order.





So, next task is to setup rotating of the letters to find the best match and use it the same way shifts are currently used (if various shifts of the letter in horizontal and vertical directions produce better match, new position is saved).
As you can see on the above passed test, letter 'N' is not placed to the left upper corner, where it was placed initially.

/devel/captcha :: Link / Comments (0)

Comments are closed for this story.