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Sun, 13 May 2007

Solving captcha problems. Rotation.


Two complex letters have been solved (letter 'N' was solved previously though) with addition of rotation around central point.




Complex letter 'F' failed:



As you can see, computer thinks that letter 'W' is the most similar letter, since it covers the maximum amount of letters, which is obviously incorrect from human point of view. Letter 'W' frequently wins just because it has too many pixels.

To solve remaining issues I plan to introduce algorithm, which will calculate number of crosses in the image. Letters with different number of crosses will be removed from the further calculations.
Actually this is simplified part of the more generic (and more complex) algo, which I have in mind. The latter should detect if it is possible to get resulted image with contiguous transformation of the lines, which form original one. It is absolutely sure that 'F' can not be obtained from letter 'W' without crossing its line with itself. But for now I will limit myself with only simplified part.

Cross-detection logic I will get from my old project to analyze pixmaps, find crosses, build a tree and then find the shortest path from one point to another.
Here is one screenshot of the middle stage of the development (will be opened with real sizes (1024x768) on-click):

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