Algorithm for Handedness Detection of Fiddler Crabs

Members of the genus Uca are generally known as Fiddler crabs for the overgrown claw of the males. The following algorithm detects a male fiddler crabs handedness from a photograph. The algorithm was implemented using Matlab R2009a.

Assumptions :
The photo was taken from front, close enough for the specimen to occupy significant portion of the frame.

Input :
Photograph in RGB format.

Procedure :

• convertRGB image to Lab format
• subtract background from l to correct non-uniform lighting, enhance the resulting image
• apply threshold
• perform morphological opening, remove blobs with area less than 200pixel
• dilate
• erode
• mark the maximum area blob, find its centroid (C1)
• find the maximum hole in maximum area blob, find hole's centroid (C2)
• if C1 has X coordinate less than C2 then it's a right handed crab, otherwise its left handed

Test results :
The following two photos of a fiddler crab I shot near the mangrove area at Rezu Khal, Cox's Bazar was used to test the algorithm. The results are correct as can be seen from the images.

Future work :
To test the algorithm with photos taken at wide range of conditions as well as of many other species.