/*
 * Copyright 2005 by the Massachusetts Institute of Technology.
 *
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting
 * documentation, and that the name of M.I.T. not be used in
 * advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is"
 * without express or implied warranty.
 */

/**
 * @description
 * This file contains components for converting between various different
 * color spaces.
 *
 * @author <a href="mailto:madrake@gmail.com">Matthew Drake</a>
 * @file ColorSpace.str
 * @version 1.0
 */

int->int pipeline ColorSpaceConversion_YCbCrtoRGB {
    add YCbCrtoRGB;
    add BestSaturation(0, 255, -384, 639);
    // See mpeg2dec in the reference implementation, Clip[]
}

int->int pipeline ColorSpaceConversion_RGBtoYCbCr {
    add RGBtoYCbCr;
}         


/**
 * Converts a pixel in RGB format to a pixel in YCbCr format according to Recommendation
 * ITU-R BT.709 for color space transformations. This is the default transformation that should
 * be used for MPEG-2 videos. This transformation is given in Table 6-9 on P.47 of the MPEG-2 13818-2
 * IEEE specification (entry #1). 
 * @input Three integers in RGB color space and order.
 * @output Three integers in YCbCr color space and order.
 */
int->int filter RGBtoYCbCr {
    work pop 3 push 3 {
        int R = pop();
        int G = pop();
        int B = pop();

        float ER = ((float) R)/256.0;
        float EG = ((float) G)/256.0;
        float EB = ((float) B)/256.0;

        float Ey =   0.715400*EG + 0.072100*EB + 0.212500*ER;
        float Epb = -0.386000*EG + 0.500000*EB - 0.115000*ER;
        float Epr = -0.454000*EG - 0.046000*EB + 0.500000*ER;

        int Y = (int) round((219*Ey) + 16);
        int Cb = (int) round((224*Epb) + 128);
        int Cr = (int) round((224*Epr) + 128);

        // My values are centered between +/- 128 and it outputs values in the
        // 0 to 255 range, so we compute and then subtract.

        push(Y-128);
        push(Cb-128);
        push(Cr-128);
    }
}

/**
 * Converts a pixel in YCbCr format to a pixel in RGB format according to Recommendation
 * ITU-R BT.709 for color space transformations. This is the default transformation that should
 * be used for MPEG-2 videos. This transformation is given in Table 6-9 on P.47 of the MPEG-2 13818-2
 * IEEE specification (entry #1). The recommendation specifies the transform from RGB to YCbCR. This
 * function's transformation coefficients were calculated using MATLAB and an inverse matrix transform
 * based on the RGB to YCbCr conversion.
 * @input Three integers in YCbCr color space and order.
 * @output Three integers in RGB color space and order.
 */
int->int filter YCbCrtoRGB {
    // My values are centered between +/- 128, and it expects values in the 
    // 0 to 255 range, so we add first and then compute.
    // Saturation of the output is performed downstream.

    work pop 3 push 3 {

        int Y = 76309 * (pop() + 112);
        int U = pop();
        int V = pop();
        int R = (Y + 117504*V + 32768)>>16;
        int G = (Y - 13954*U - 34903*V + 32768)>>16;
        int B = (Y + 138453*U + 32786)>>16;

        push(R);
        push(G);
        push(B);

    }
}