Learning OpenCV, 2nd Edition

HSV histograms, where the vertical axis is 𝑉 (value), the radius is 𝑆 (saturation) and the angle is 𝐻 (hue).

Notice that indoors is the darkest, outdoors in shadow in is a bit brighter, and outdoors in the sun is the

brightest. Note also that the colors shift around somewhat as a result of the changing color of the

illuminating light.

Figure 7-6: Histogram of flesh colors under indoor (upper-left), shadowed outdoor (middle left), and direct

sun outdoor (lower-left) lighting conditions; the middle and right-hand columns display the associated BGR

and HSV histograms, respectively

As a test of histogram comparison, we could take a portion of one palm (e.g., the top half of the indoor

palm), and compare the histogram representation of the colors in that image either with the histogram

representation of the colors in the remainder of that image or with the histogram representations of the

other two hand images. To make a lower dimensional comparison, we use only hue (𝐻) and saturation (𝑆)

from an HSV color space.

Table 7-1: Histogram comparison, via four matching methods, of palm-flesh colors in upper half of indoor

palm with listed variant palm-flesh color. We used 30 bins for hue, and 32 for saturation. For reference,

the expected score for a perfect match is provided in the first row.

Comparison

CORREL

CHISQR

INTERSECT

BHATTACHARYYA ...