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Just as an addition to my remark, these are actually the codes for formatting an imread:

/* 8 bit, color or gray - deprecated, use CV_LOAD_IMAGE_ANYCOLOR */
#define CV_LOAD_IMAGE_UNCHANGED  -1
/* 8 bit, gray */
#define CV_LOAD_IMAGE_GRAYSCALE   0
/* 8 bit unless combined with CV_LOAD_IMAGE_ANYDEPTH, color */
#define CV_LOAD_IMAGE_COLOR       1
/* any depth, if specified on its own gray */
#define CV_LOAD_IMAGE_ANYDEPTH    2
/* by itself equivalent to CV_LOAD_IMAGE_UNCHANGED
   but can be modified with CV_LOAD_IMAGE_ANYDEPTH */
#define CV_LOAD_IMAGE_ANYCOLOR    4

So you can see that the imread with the color option, creates an 8 bit 3 channel image.