Which algorithm or library can I use for duplicate Image detection on map tiles? [closed]

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I am converting PNG images to 256x256 PNG dimension tiles. I would like to detect nearly identical tiles (like blue water or white background tiles or gaps on floor plans) A lot of tiles cannot be distinguished by the eye but have nevertheless some different pixels so a md5 hash doesn't do the work... what else can I try?

Answer 1

I'm not sure of the spot offhand, but TileMill does this and is open source (http://github.com/mapbox/tilemill). It may defer to Mapnik for the de-dupe. One thing to keep in mind is that once you've determined a tile is a duplicate, you can also discount all tiles below it in the "pyramid" -- for example, a single tile is four tiles in the next zoom level down, and each of those is another four in the next zoom etc.