Image histogram equalization YCbCr bug.

[KKyang]

Currently YCbCr is using uchar to store information cause data losses.

Two solutions:

1. Change to HSV.
2. Fix YCbCr. (Use float instead of uchar)

[KKyang]

http://docs.opencv.org/modules/imgproc/doc/miscellaneous_transformations.html

Still fixing on YCbCr conversion. HSV version works well.