From: Greg Blair <gblair@sympatico.ca>
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Subject: Re: RGB -> YIQ(4:2:2, 4:2:0) Source Code ?
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Hello kevin,

YIQ is only used in encoding/decoding NTSC composite video.  For
digital, you most likely need what is commonly referred to as YUV or
more correctly Y'CbCr.  This is the format used in Rec 609 video,
commonly referred to as D1 video.

// see http://home.earthlink.net/~janos1/vidpage/color_faq.html
// +----------------+---------------+-----------------+----------------+

// | Recommendation | Coef. for red | Coef. for Green | Coef. for Blue |

// +----------------+---------------+-----------------+----------------+

// | Rec 601-1      | 0.2989        | 0.5866          | 0.1145         |

// | Rec 709        | 0.2125        | 0.7154          | 0.0721         |

// | SMPTE 295M-1997| 0.2126        | 0.7152          | 0.0722         |

// | ITU            | 0.2220        | 0.7067          | 0.0713         |

// +----------------+---------------+-----------------+----------------+

// (use Rec 601 for SDTV and SMPTE 295M (4th decimal difference from Rec 709) for HDTV)

// RGB -> YCbCr
// Y  = Coef. for red*Red+Coef. for green*Green+Coef. for blue*Blue
// Cb = (Blue-Y)/(2-2*Coef. for blue)
// Cr = (Red-Y)/(2-2*Coef. for red)
// YCbCr -> RGB
// Red   = Cr*(2-2*Coef. for red)+Y
// Green = (Y-Coef. for blue*Blue-Coef. for red*Red)/Coef. for green
// Blue  = Cb*(2-2*Coef. for blue)+Y


void RGBto422 (unsigned char *rgb, unsigned char *yuv, int width, int
height)
{
    int r, g, b, Y1, Cb1, Cr1, Y2, Cb2, Cr2, x, y;
    for(y = 0; y<height; y++)
        for(x = 0; x < width; x += 2) {
            r = *rgb++;
            g = *rgb++;
            b = *rgb++;

            Y1 = 0.2989 * r + 0.5866 * g + 0.1145 * b;
            Cb1 = (b - Y1) / (2. - 2. * 0.1145);
            Cr1 = (r - Y1) / (2. - 2. * 0.2989);

            r = *rgb++;
            g = *rgb++;
            b = *rgb++;

            Y2 = 0.2989 * r + 0.5866 * g + 0.1145 * b;
            Cb2 = (b - Y2) / (2. - 2. * 0.1145);
            Cr2 = (r - Y2) / (2. - 2. * 0.2989);

            *yuv++ = (unsigned char) (128 + (Cb1 + Cb2) / 2) * 224./255.+ 16;
            *yuv++ = (unsigned char) Y1 * 219./255/ + 16;
            *yuv++ = (unsigned char) (128 + (Cr1 + Cr2) / 2) * 224./255.+ 16;
            *yuv++ = (unsigned char) Y2 * 219./255/ + 16;

        }
}

//a nd for completeness 411:

void RGBto420 (unsigned char *rgb, unsigned char *yuv, int width, int
height)
{
    int r, g, b, Y1, Cb1, Cr1, Y2, Cb2, Cr2, Y3, Cb3, Cr3, Y4, Cb4, Cr4,
x, y;
    for(y = 0; y<height; y += 2)
        for(x = 0; x < width; x += 2) {
            r = *rgb;
            g = *(rgb+1);
            b = *(rgb+2);

            Y1 = 0.2989 * r + 0.5866 * g + 0.1145 * b;
            Cb1 = (b - Y1) / (2. - 2. * 0.1145);
            Cr1 = (r - Y1) / (2. - 2. * 0.2989);

            r = *(rgb+3);
            g = *(rgb+4);
            b = *(rgb+5);

            Y2 = 0.2989 * r + 0.5866 * g + 0.1145 * b;
            Cb2 = (b - Y2) / (2. - 2. * 0.1145);
            Cr2 = (r - Y2) / (2. - 2. * 0.2989);

            r = *(rgb+3*width);
            g = *(rgb+3*width+1);
            b = *(rgb+3*width+2);

            Y3 = 0.2989 * r + 0.5866 * g + 0.1145 * b;
            Cb3 = (b - Y3) / (2. - 2. * 0.1145);
            Cr3 = (r - Y3) / (2. - 2. * 0.2989);

            r = *(rgb+3*width+3);
            g = *(rgb+3*width+4);
            b = *(rgb+3*width+5);

            Y4 = 0.2989 * r + 0.5866 * g + 0.1145 * b;
            Cb4 = (b - Y4) / (2. - 2. * 0.1145);
            Cr4 = (r - Y4) / (2. - 2. * 0.2989);

            *yuv++ = (unsigned char) Y1 * 219./255/ + 16;
            *yuv++ = (unsigned char) Y2 * 219./255/ + 16;
            *yuv++ = (unsigned char) Y3 * 219./255/ + 16;
            *yuv++ = (unsigned char) Y4 * 219./255/ + 16;
            *yuv++ = (unsigned char) (128 + (Cb1 + Cb2 + Cb3 + Cb4) / 4) * 224./255. + 16;
            *yuv++ = (unsigned char) (128 + (Cr1 + Cr2 + Cr3 + Cr4) / 4) * 224./255. + 16;

            rgb += 6;
        }
}

void RGBto411 (unsigned char *rgb, unsigned char *yuv, int width, int
height)
{
    int r, g, b, Y1, Cb1, Cr1, Y2, Cb2, Cr2, Y3, Cb3, Cr3, Y4, Cb4, Cr4,
x, y;
    for(y = 0; y<height; y++)
        for(x = 0; x < width; x += 4) {
            r = *rgb++;
            g = *rgb++;
            b = *rgb++;

            Y1 = 0.2989 * r + 0.5866 * g + 0.1145 * b;
            Cb1 = (b - Y1) / (2. - 2. * 0.1145);
            Cr1 = (r - Y1) / (2. - 2. * 0.2989);

            r = *rgb++;
            g = *rgb++;
            b = *rgb++;

            Y2 = 0.2989 * r + 0.5866 * g + 0.1145 * b;
            Cb2 = (b - Y2) / (2. - 2. * 0.1145);
            Cr2 = (r - Y2) / (2. - 2. * 0.2989);

            r = *rgb++;
            g = *rgb++;
            b = *rgb++;

            Y3 = 0.2989 * r + 0.5866 * g + 0.1145 * b;
            Cb3 = (b - Y3) / (2. - 2. * 0.1145);
            Cr3 = (r - Y3) / (2. - 2. * 0.2989);

            r = *rgb++;
            g = *rgb++;
            b = *rgb++;

            Y4 = 0.2989 * r + 0.5866 * g + 0.1145 * b;
            Cb4 = (b - Y4) / (2. - 2. * 0.1145);
            Cr4 = (r - Y4) / (2. - 2. * 0.2989);

            *yuv++ = (unsigned char) Y1 * 219./255/ + 16;
            *yuv++ = (unsigned char) Y2 * 219./255/ + 16;
            *yuv++ = (unsigned char) Y3 * 219./255/ + 16;
            *yuv++ = (unsigned char) Y4 * 219./255/ + 16;
            *yuv++ = (unsigned char) (128 + (Cb1 + Cb2 + Cb3 + Cb4) / 4) * 224./255. + 16;
            *yuv++ = (unsigned char) (128 + (Cr1 + Cr2 + Cr3 + Cr4) / 4) * 224./255. + 16;
        }
}

Now you can optimize using scaled fraction arithmetic or MMX assembler
code.

The definitive reference for video and video color space conversion is
Video Demystified, by Jack Keith (http://www.video-demystified.com/)

Enjoy!

Cheers,  Greg Blair


Kevin Paek wrote:

> Dear All!
>
> I am looking for Source Code of RGB -> YIQ(4:2:2, 4:2:0).