Several different methods of color image turning grayscale

Recently in the analysis of several open source image processing programs, found several different color image to grayscale method, the method is very simple, but also very easy to understand, but the effect is obviously different. Before introducing the method of calculation, the difference between brightness (lightness) and illuminance (luminosity) should be mentioned first. Brightness (lightness), refers to the light that people feel when they see it. Illuminance (luminosity), refers to the light source on the object, the unit is irradiated area on the luminous flux. It can be said that brightness is the body reflected light to the strength of the eye, is a subjective sense of the person, and illuminance is the light source on the object of strength, is an objective physical quantity. The same light source, the same distance on white and black paper, brightness is different, illuminance is the same. The following is a simple code example:

1. Method based on the mean value:

Uchar *psrcimg = src.data;for (int i = 0; i < src.rows; i++) {for (int j = 0; J < Src.cols; J + +, psrcimg + = 3) {Double Average = (Psrcimg[0] + psrcimg[1] + psrcimg[2])/3;psrcimg[0] = (uchar) min (255, average);p srcimg[1] = (uchar) min (255, a verage);p srcimg[2] = (UCHAR) MIN (255, average);}}

2. Brightness-based method:

Uchar *psrcimg = src.data;for (int i = 0; i < src.rows; i++) {for (int j = 0; J < Src.cols; J + +, psrcimg + = 3) {Uchar Max_val = Max (psrcimg[0], psrcimg[1]); max_val = max (Max_val, psrcimg[2]); Uchar min_val = min (psrcimg[0], psrcimg[1]); min _val = min (Min_val, psrcimg[2]);d ouble lightness = (max_val + min_val)/2;psrcimg[0] = (UCHAR) MIN (255, lightness);p srcimg [1] = (uchar) min (255, lightness);p srcimg[2] = (uchar) min (255, lightness);}}

3. Illuminance-Based approach:

HDTV with Bt.709uchar *psrcimg = src.data;for (int i = 0; i < src.rows; i++) {for (int j = 0; J < Src.cols; j + +, p Srcimg + = 3) {Double luminosity = psrcimg[0] * 0.0722 + psrcimg[1] * 0.7152 + psrcimg[2] * 0.2126;psrcimg[0] = (UCHAR) MIN (2 luminosity);p srcimg[1] = (uchar) min (255, luminosity);p srcimg[2] = (UCHAR) MIN (255, luminosity);}}

SDTV with Bt.601uchar *psrcimg = src3.data;for (int i = 0; i < src.rows; i++) {for (int j = 0; J < Src.cols; J + +, Psrcimg + = 3) {Double luminosity = psrcimg[0] * 0.114 + psrcimg[1] * 0.587 + psrcimg[2] * 0.299;psrcimg[0] = (UCHAR) MIN (255 , luminosity);p srcimg[1] = (uchar) min (255, luminosity);p srcimg[2] = (UCHAR) MIN (255, luminosity);}}

Here are some of the conversion methods described above:

Several different methods of color image turning grayscale