c++ - Pixels in YUV image -

i using opencv achieve object tracking. read yuv image better option use rgb image. problem fail understand yuv format although spend time read notes. y brightness believe calculated combination of r, g, b component.

my main problem how can access , manipulate pixels in yuv image format. in rgb format easy access component , therefore change using simple operatin

src.at<vec3b>(j,i).val[0] = 0; example 

but not case in yuv. need in accessing , changing pixel values in yuv image. example if pixel in rgb red, want keep corresponding pixel in yuv , rest removed. please me this.

i suggest operating on image in hsv or lab rather rgb.

the raw image camera in ycbcr (sometimes called yuv, think incorrect, may wrong), , laid out in way resembles yuyv (repeating), if can convert directly hsv, avoid additional copy , conversion operations save time. may matter if you're processing video or batches of images however.

here's c++ code converting between ycbcr , rgb (one uses integer math, other floating point):

colour::bgr colour::ycbcr::tobgrint() const {   int c0 = 22987;   int c1 = -11698;   int c2 = -5636;   int c3 = 29049;    int y = this->y;   int cb = this->cb - 128;   int cr = this->cr - 128;    int b = y + (((c3 * cb) + (1 << 13)) >> 14);   int g = y + (((c2 * cb + c1 * cr) + (1 << 13)) >> 14);   int r = y + (((c0 * cr) + (1 << 13)) >> 14);    if (r < 0)     r = 0;   else if (r > 255)     r = 255;    if (g < 0)     g = 0;   else if (g > 255)     g = 255;    if (b < 0)     b = 0;   else if (b > 255)     b = 255;    return colour::bgr(b, g, r); }  colour::bgr colour::ycbcr::tobgrfloat() const {   float y = this->y;   float cb = this->cb;   float cr = this->cr;    int r = y + 1.40200 * (cr - 0x80);   int g = y - 0.34414 * (cb - 0x80) - 0.71414 * (cr - 0x80);   int b = y + 1.77200 * (cb - 0x80);    if (r < 0)     r = 0;   else if (r > 255)     r = 255;    if (g < 0)     g = 0;   else if (g > 255)     g = 255;    if (b < 0)     b = 0;   else if (b > 255)     b = 255;    return colour::bgr(b, g, r); } 

and conversion bgr hsv:

colour::hsv colour::bgr2hsv(bgr const& in) {   colour::hsv out;    int const hstep = 255 / 3;            // hue step size between red -> green -> blue    int min = in.r < in.g ? in.r : in.g;   min = min  < in.b ? min  : in.b;    int max = in.r > in.g ? in.r : in.g;   max = max  > in.b ? max  : in.b;    out.v = max;                          // v   int chroma = max - min;   if (max > 0)   {     out.s = 255 * chroma / max;         // s   }   else   {     // r = g = b = 0                    // s = 0, v undefined     out.s = 0;     out.h = 0;     out.v = 0; // it's undefined     return out;   }    if (chroma == 0)   {     out.h = 0;     return out;   }    const int chroma2 = chroma * 2;   int offset;   int diff;    if (in.r == max)   {     offset = 3 * hstep;     diff = in.g - in.b;   }   else if (in.g == max)   {     offset = hstep;     diff = in.b - in.r;   }   else   {     offset = 2 * hstep;     diff = in.r - in.g;   }    int h = offset + (diff * (hstep + 1)) / chroma2;    // rotate such red has hue 0   if (h >= 255)     h -= 255;    assert(h >= 0 && h < 256);    out.h = h;    return out; 

unfortunately not have code in 1 step.

you can use built-in opencv functions colour conversion.

cvtcolor(img, img, cv_bgr2hsv);