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The HSV color wheel can be used for color complementary, analogous such as color distance. The H channel from OpenCV BGR2HSV conversion is the Hue, in other words is the angle of the color on the color wheel. You might consider the difference between hues as colors distance without involve darkness or lightness.

Remember that

• hue is a angle over a circle than you have to get the shortest path between 2 hues (clockwise and counter-clockwise). For example hue=1 is RED, hue=120deg is GREEN and hue=330deg is ROSE
• In OpenCV the hue range 0..360deg is scaled down to 0..180 (or 0..255 if COLOR_BGR2HSV_FULL is used)

Using the conversion as @LBerger answer, this should check color distance between pt1 and pt2

Point pt1(x1,y1), p2(x2,y2);
Vec3b hsv1 = hsv.at<Vec3b>(p1); // get HSV values for the pixel. Hue is the 1st in the vector
Vec3b hsv2 = hsv.at<Vec3b>(p2);
d1 = abs(hsv1(0)-hsv2(0));  // absolute distance
d = min(d1,180-d1); // correct distance if cross 0deg . full circle at 180 because of Hue scaling

The HSV color wheel can be used for color complementary, analogous such as color distance. The H channel from OpenCV BGR2HSV conversion is the Hue, in other words is the angle of the color on the color wheel. You might consider the difference between hues as colors distance without involve darkness or lightness.

Remember that

• hue is a angle over a circle than you have to get the shortest path between 2 hues (clockwise and counter-clockwise). For example hue=1 hue=1° is RED, hue=120deg hue=120° is GREEN and hue=330deg is ROSEhue=330° is ROSE. RED -> ROSE = 31° and RED -> GREEN = 119° !
• In OpenCV the hue range 0..360deg is scaled down to 0..180 (or 0..255 if COLOR_BGR2HSV_FULL is used)

Using the conversion as @LBerger answer, this should check color distance between pt1 and pt2

Point pt1(x1,y1), p2(x2,y2);
Vec3b hsv1 = hsv.at<Vec3b>(p1); // get HSV values for the pixel. Hue is the 1st in the vector
Vec3b hsv2 = hsv.at<Vec3b>(p2);
d1 = abs(hsv1(0)-hsv2(0));  // absolute distance
d = min(d1,180-d1); // correct distance if cross 0deg . full circle at 180 because of Hue scaling

The HSV color wheel can be used for color complementary, analogous such as color distance. The H channel from OpenCV BGR2HSV conversion is the Hue, in other words is the angle of the color on the color wheel. You might consider the difference between hues as colors distance without involve darkness or lightness.

Remember that

• hue is a angle over a circle than you have to get the shortest path between 2 hues (clockwise and counter-clockwise). For example hue=1° is RED, hue=120° is GREEN and hue=330° is ROSE. RED -> ROSE = 31° and RED -> GREEN = 119° !
• In OpenCV OpenCV, 3x8bit images, the hue range 0..360deg is scaled down to 0..180 0..180 (or 0..255 if COLOR_BGR2HSV_FULL is used)used). Therefore GREEN is 60 (or 85 in case of _FULL conversion).

Using the conversion as @LBerger answer, this should check color distance between pt1 and pt2

Point pt1(x1,y1), p2(x2,y2);
Vec3b hsv1 = hsv.at<Vec3b>(p1); // get HSV values for the pixel. Hue is the 1st in the vector
Vec3b hsv2 = hsv.at<Vec3b>(p2);
d1 = abs(hsv1(0)-hsv2(0));  // absolute distance
d = min(d1,180-d1); // correct distance if cross 0deg . full circle at 180 because of Hue scaling