ImfRgbaYca.cpp

//////////////////////////////////////////////////////////////////////////////
//
// Copyright (c) 2004, Industrial Light & Magic, a division of Lucasfilm
// Entertainment Company Ltd.  Portions contributed and copyright held by
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//////////////////////////////////////////////////////////////////////////////

//-----------------------------------------------------------------------------
//
//	Conversion between RGBA and YCA data.
//
//-----------------------------------------------------------------------------

#include <ImfRgbaYca.h>
#include <assert.h>
#include <algorithm>

using namespace Imath;
using namespace std;

namespace Imf {
namespace RgbaYca {


V3f
computeYw (const Chromaticities &cr)
{
    M44f m = RGBtoXYZ (cr, 1);
    return V3f (m[0][1], m[1][1], m[2][1]) / (m[0][1] + m[1][1] + m[2][1]);
}


void
RGBAtoYCA (const V3f &yw,
       int n,
       bool aIsValid,
       const Rgba rgbaIn[/*n*/],
       Rgba ycaOut[/*n*/])
{
    for (int i = 0; i < n; ++i)
    {
    Rgba in = rgbaIn[i];
    Rgba &out = ycaOut[i];

    //
    // Conversion to YCA and subsequent chroma subsampling
    // work only if R, G and B are finite and non-negative.
    //

    if (!in.r.isFinite() || in.r < 0)
        in.r = 0;

    if (!in.g.isFinite() || in.g < 0)
        in.g = 0;

    if (!in.b.isFinite() || in.b < 0)
        in.b = 0;

    if (in.r == in.g && in.g == in.b)
    {
        //
        // Special case -- R, G and B are equal. To avoid rounding
        // errors, we explicitly set the output luminance channel
        // to G, and the chroma channels to 0.
        //
        // The special cases here and in YCAtoRGBA() ensure that
        // converting black-and white images from RGBA to YCA and
        // back is lossless.
        //

        out.r = 0;
        out.g = in.g;
        out.b = 0;
    }
    else
    {
        out.g = in.r * yw.x + in.g * yw.y + in.b * yw.z;

        float Y = out.g;

        if (abs (in.r - Y) < HALF_MAX * Y)
        out.r = (in.r - Y) / Y;
        else
        out.r = 0;

        if (abs (in.b - Y) < HALF_MAX * Y)
        out.b = (in.b - Y) / Y;
        else
        out.b = 0;
    }

    if (aIsValid)
        out.a = in.a;
    else
        out.a = 1;
    }
}


void
decimateChromaHoriz (int n,
             const Rgba ycaIn[/*n+N-1*/],
             Rgba ycaOut[/*n*/])
{
    #ifdef DEBUG
    assert (ycaIn != ycaOut);
    #endif

    int begin = N2;
    int end = begin + n;

    for (int i = begin, j = 0; i < end; ++i, ++j)
    {
    if ((j & 1) == 0)
    {
        ycaOut[j].r = ycaIn[i - 13].r *  0.001064f +
              ycaIn[i - 11].r * -0.003771f +
              ycaIn[i -  9].r *  0.009801f +
              ycaIn[i -  7].r * -0.021586f +
              ycaIn[i -  5].r *  0.043978f +
              ycaIn[i -  3].r * -0.093067f +
              ycaIn[i -  1].r *  0.313659f +
              ycaIn[i     ].r *  0.499846f +
              ycaIn[i +  1].r *  0.313659f +
              ycaIn[i +  3].r * -0.093067f +
              ycaIn[i +  5].r *  0.043978f +
              ycaIn[i +  7].r * -0.021586f +
              ycaIn[i +  9].r *  0.009801f +
              ycaIn[i + 11].r * -0.003771f +
              ycaIn[i + 13].r *  0.001064f;

        ycaOut[j].b = ycaIn[i - 13].b *  0.001064f +
              ycaIn[i - 11].b * -0.003771f +
              ycaIn[i -  9].b *  0.009801f +
              ycaIn[i -  7].b * -0.021586f +
              ycaIn[i -  5].b *  0.043978f +
              ycaIn[i -  3].b * -0.093067f +
              ycaIn[i -  1].b *  0.313659f +
              ycaIn[i     ].b *  0.499846f +
              ycaIn[i +  1].b *  0.313659f +
              ycaIn[i +  3].b * -0.093067f +
              ycaIn[i +  5].b *  0.043978f +
              ycaIn[i +  7].b * -0.021586f +
              ycaIn[i +  9].b *  0.009801f +
              ycaIn[i + 11].b * -0.003771f +
              ycaIn[i + 13].b *  0.001064f;
    }

    ycaOut[j].g = ycaIn[i].g;
    ycaOut[j].a = ycaIn[i].a;
    }
}


void
decimateChromaVert (int n,
            const Rgba * const ycaIn[N],
            Rgba ycaOut[/*n*/])
{
    for (int i = 0; i < n; ++i)
    {
    if ((i & 1) == 0)
    {
        ycaOut[i].r = ycaIn[ 0][i].r *  0.001064f +
              ycaIn[ 2][i].r * -0.003771f +
              ycaIn[ 4][i].r *  0.009801f +
              ycaIn[ 6][i].r * -0.021586f +
              ycaIn[ 8][i].r *  0.043978f +
              ycaIn[10][i].r * -0.093067f +
              ycaIn[12][i].r *  0.313659f +
              ycaIn[13][i].r *  0.499846f +
              ycaIn[14][i].r *  0.313659f +
              ycaIn[16][i].r * -0.093067f +
              ycaIn[18][i].r *  0.043978f +
              ycaIn[20][i].r * -0.021586f +
              ycaIn[22][i].r *  0.009801f +
              ycaIn[24][i].r * -0.003771f +
              ycaIn[26][i].r *  0.001064f;

        ycaOut[i].b = ycaIn[ 0][i].b *  0.001064f +
              ycaIn[ 2][i].b * -0.003771f +
              ycaIn[ 4][i].b *  0.009801f +
              ycaIn[ 6][i].b * -0.021586f +
              ycaIn[ 8][i].b *  0.043978f +
              ycaIn[10][i].b * -0.093067f +
              ycaIn[12][i].b *  0.313659f +
              ycaIn[13][i].b *  0.499846f +
              ycaIn[14][i].b *  0.313659f +
              ycaIn[16][i].b * -0.093067f +
              ycaIn[18][i].b *  0.043978f +
              ycaIn[20][i].b * -0.021586f +
              ycaIn[22][i].b *  0.009801f +
              ycaIn[24][i].b * -0.003771f +
              ycaIn[26][i].b *  0.001064f;
    }

    ycaOut[i].g = ycaIn[13][i].g;
    ycaOut[i].a = ycaIn[13][i].a;
    }
}


void
roundYCA (int n,
      unsigned int roundY,
      unsigned int roundC,
      const Rgba ycaIn[/*n*/],
      Rgba ycaOut[/*n*/])
{
    for (int i = 0; i < n; ++i)
    {
    ycaOut[i].g = ycaIn[i].g.round (roundY);
    ycaOut[i].a = ycaIn[i].a;

    if ((i & 1) == 0)
    {
        ycaOut[i].r = ycaIn[i].r.round (roundC);
        ycaOut[i].b = ycaIn[i].b.round (roundC);
    }
    }
}


void
reconstructChromaHoriz (int n,
            const Rgba ycaIn[/*n+N-1*/],
            Rgba ycaOut[/*n*/])
{
    #ifdef DEBUG
    assert (ycaIn != ycaOut);
    #endif

    int begin = N2;
    int end = begin + n;

    for (int i = begin, j = 0; i < end; ++i, ++j)
    {
    if (j & 1)
    {
        ycaOut[j].r = ycaIn[i - 13].r *  0.002128f +
              ycaIn[i - 11].r * -0.007540f +
              ycaIn[i -  9].r *  0.019597f +
              ycaIn[i -  7].r * -0.043159f +
              ycaIn[i -  5].r *  0.087929f +
              ycaIn[i -  3].r * -0.186077f +
              ycaIn[i -  1].r *  0.627123f +
              ycaIn[i +  1].r *  0.627123f +
              ycaIn[i +  3].r * -0.186077f +
              ycaIn[i +  5].r *  0.087929f +
              ycaIn[i +  7].r * -0.043159f +
              ycaIn[i +  9].r *  0.019597f +
              ycaIn[i + 11].r * -0.007540f +
              ycaIn[i + 13].r *  0.002128f;

        ycaOut[j].b = ycaIn[i - 13].b *  0.002128f +
              ycaIn[i - 11].b * -0.007540f +
              ycaIn[i -  9].b *  0.019597f +
              ycaIn[i -  7].b * -0.043159f +
              ycaIn[i -  5].b *  0.087929f +
              ycaIn[i -  3].b * -0.186077f +
              ycaIn[i -  1].b *  0.627123f +
              ycaIn[i +  1].b *  0.627123f +
              ycaIn[i +  3].b * -0.186077f +
              ycaIn[i +  5].b *  0.087929f +
              ycaIn[i +  7].b * -0.043159f +
              ycaIn[i +  9].b *  0.019597f +
              ycaIn[i + 11].b * -0.007540f +
              ycaIn[i + 13].b *  0.002128f;
    }
    else
    {
        ycaOut[j].r = ycaIn[i].r;
        ycaOut[j].b = ycaIn[i].b;
    }

    ycaOut[j].g = ycaIn[i].g;
    ycaOut[j].a = ycaIn[i].a;
    }
}


void
reconstructChromaVert (int n,
               const Rgba * const ycaIn[N],
               Rgba ycaOut[/*n*/])
{
    for (int i = 0; i < n; ++i)
    {
    ycaOut[i].r = ycaIn[ 0][i].r *  0.002128f +
              ycaIn[ 2][i].r * -0.007540f +
              ycaIn[ 4][i].r *  0.019597f +
              ycaIn[ 6][i].r * -0.043159f +
              ycaIn[ 8][i].r *  0.087929f +
              ycaIn[10][i].r * -0.186077f +
              ycaIn[12][i].r *  0.627123f +
              ycaIn[14][i].r *  0.627123f +
              ycaIn[16][i].r * -0.186077f +
              ycaIn[18][i].r *  0.087929f +
              ycaIn[20][i].r * -0.043159f +
              ycaIn[22][i].r *  0.019597f +
              ycaIn[24][i].r * -0.007540f +
              ycaIn[26][i].r *  0.002128f;

    ycaOut[i].b = ycaIn[ 0][i].b *  0.002128f +
              ycaIn[ 2][i].b * -0.007540f +
              ycaIn[ 4][i].b *  0.019597f +
              ycaIn[ 6][i].b * -0.043159f +
              ycaIn[ 8][i].b *  0.087929f +
              ycaIn[10][i].b * -0.186077f +
              ycaIn[12][i].b *  0.627123f +
              ycaIn[14][i].b *  0.627123f +
              ycaIn[16][i].b * -0.186077f +
              ycaIn[18][i].b *  0.087929f +
              ycaIn[20][i].b * -0.043159f +
              ycaIn[22][i].b *  0.019597f +
              ycaIn[24][i].b * -0.007540f +
              ycaIn[26][i].b *  0.002128f;

    ycaOut[i].g = ycaIn[13][i].g;
    ycaOut[i].a = ycaIn[13][i].a;
    }
}


void
YCAtoRGBA (const Imath::V3f &yw,
       int n,
       const Rgba ycaIn[/*n*/],
       Rgba rgbaOut[/*n*/])
{
    for (int i = 0; i < n; ++i)
    {
    const Rgba &in = ycaIn[i];
    Rgba &out = rgbaOut[i];

    if (in.r == 0 && in.b == 0)
    {
        //
        // Special case -- both chroma channels are 0.  To avoid
        // rounding errors, we explicitly set the output R, G and B
        // channels equal to the input luminance.
        //
        // The special cases here and in RGBAtoYCA() ensure that
        // converting black-and white images from RGBA to YCA and
        // back is lossless.
        //

        out.r = in.g;
        out.g = in.g;
        out.b = in.g;
        out.a = in.a;
    }
    else
    {
        float Y =  in.g;
        float r = (in.r + 1) * Y;
        float b = (in.b + 1) * Y;
        float g = (Y - r * yw.x - b * yw.z) / yw.y;

        out.r = r;
        out.g = g;
        out.b = b;
        out.a = in.a;
    }
    }
}


namespace {

inline float
saturation (const Rgba &in)
{
    float rgbMax = max (in.r, max (in.g, in.b));
    float rgbMin = min (in.r, min (in.g, in.b));

    if (rgbMax > 0)
    return 1 - rgbMin / rgbMax;
    else
    return 0;
}


void
desaturate (const Rgba &in, float f, const V3f &yw, Rgba &out)
{
    float rgbMax = max (in.r, max (in.g, in.b));

    out.r = max (float (rgbMax - (rgbMax - in.r) * f), 0.0f);
    out.g = max (float (rgbMax - (rgbMax - in.g) * f), 0.0f);
    out.b = max (float (rgbMax - (rgbMax - in.b) * f), 0.0f);
    out.a = in.a;

    float Yin  = in.r  * yw.x + in.g  * yw.y + in.b  * yw.z;
    float Yout = out.r * yw.x + out.g * yw.y + out.b * yw.z;

    if (Yout > 0)
    {
    out.r *= Yin / Yout;
    out.g *= Yin / Yout;
    out.b *= Yin / Yout;
    }
}

} // namespace


void
fixSaturation (const Imath::V3f &yw,
           int n,
           const Rgba * const rgbaIn[3],
           Rgba rgbaOut[/*n*/])
{
    float neighborA2 = saturation (rgbaIn[0][0]);
    float neighborA1 = neighborA2;

    float neighborB2 = saturation (rgbaIn[2][0]);
    float neighborB1 = neighborB2;

    for (int i = 0; i < n; ++i)
    {
    float neighborA0 = neighborA1;
    neighborA1 = neighborA2;

    float neighborB0 = neighborB1;
    neighborB1 = neighborB2;

    if (i < n - 1)
    {
        neighborA2 = saturation (rgbaIn[0][i + 1]);
        neighborB2 = saturation (rgbaIn[2][i + 1]);
    }

    //
    // A0       A1       A2
    //      rgbaOut[i]
    // B0       B1       B2
    //

    float sMean = min (1.0f, 0.25f * (neighborA0 + neighborA2 +
                      neighborB0 + neighborB2));

    const Rgba &in  = rgbaIn[1][i];
    Rgba &out = rgbaOut[i];

    float s = saturation (in);

    if (s > sMean)
    {
        float sMax = min (1.0f, 1 - (1 - sMean) * 0.25f);

        if (s > sMax)
        {
        desaturate (in, sMax / s, yw, out);
        continue;
        }
    }

    out = in;
    }
}

} // namespace RgbaYca
} // namespace Imf