imfrgbayca.cpp

image converter source code

//////////////////////////////////////////////////////////////////////////////
//
// Copyright (c) 2004, Industrial Light & Magic, a division of Lucasfilm
// Entertainment Company Ltd.  Portions contributed and copyright held by
// others as indicated.  All rights reserved.
//
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// met:
//
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//       disclaimer.
//
//     * Redistributions in binary form must reproduce the above
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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 *  0.001064 +
			  ycaIn[i - 11].r * -0.003771 +
			  ycaIn[i -  9].r *  0.009801 +
			  ycaIn[i -  7].r * -0.021586 +
			  ycaIn[i -  5].r *  0.043978 +
			  ycaIn[i -  3].r * -0.093067 +
			  ycaIn[i -  1].r *  0.313659 +
			  ycaIn[i     ].r *  0.499846 +
			  ycaIn[i +  1].r *  0.313659 +
			  ycaIn[i +  3].r * -0.093067 +
			  ycaIn[i +  5].r *  0.043978 +
			  ycaIn[i +  7].r * -0.021586 +
			  ycaIn[i +  9].r *  0.009801 +
			  ycaIn[i + 11].r * -0.003771 +
			  ycaIn[i + 13].r *  0.001064;

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

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

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

	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 *  0.002128 +
			  ycaIn[i - 11].r * -0.007540 +
			  ycaIn[i -  9].r *  0.019597 +
			  ycaIn[i -  7].r * -0.043159 +
			  ycaIn[i -  5].r *  0.087929 +
			  ycaIn[i -  3].r * -0.186077 +
			  ycaIn[i -  1].r *  0.627123 +
			  ycaIn[i +  1].r *  0.627123 +
			  ycaIn[i +  3].r * -0.186077 +
			  ycaIn[i +  5].r *  0.087929 +
			  ycaIn[i +  7].r * -0.043159 +
			  ycaIn[i +  9].r *  0.019597 +
			  ycaIn[i + 11].r * -0.007540 +
			  ycaIn[i + 13].r *  0.002128;

	    ycaOut[j].b = ycaIn[i - 13].b *  0.002128 +
			  ycaIn[i - 11].b * -0.007540 +
			  ycaIn[i -  9].b *  0.019597 +
			  ycaIn[i -  7].b * -0.043159 +
			  ycaIn[i -  5].b *  0.087929 +
			  ycaIn[i -  3].b * -0.186077 +
			  ycaIn[i -  1].b *  0.627123 +
			  ycaIn[i +  1].b *  0.627123 +
			  ycaIn[i +  3].b * -0.186077 +
			  ycaIn[i +  5].b *  0.087929 +
			  ycaIn[i +  7].b * -0.043159 +
			  ycaIn[i +  9].b *  0.019597 +
			  ycaIn[i + 11].b * -0.007540 +
			  ycaIn[i + 13].b *  0.002128;
	}
	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 *  0.002128 +
		      ycaIn[ 2][i].r * -0.007540 +
		      ycaIn[ 4][i].r *  0.019597 +
		      ycaIn[ 6][i].r * -0.043159 +
		      ycaIn[ 8][i].r *  0.087929 +
		      ycaIn[10][i].r * -0.186077 +
		      ycaIn[12][i].r *  0.627123 +
		      ycaIn[14][i].r *  0.627123 +
		      ycaIn[16][i].r * -0.186077 +
		      ycaIn[18][i].r *  0.087929 +
		      ycaIn[20][i].r * -0.043159 +
		      ycaIn[22][i].r *  0.019597 +
		      ycaIn[24][i].r * -0.007540 +
		      ycaIn[26][i].r *  0.002128;

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

	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*/])
{
    for (int i = 0; i < n; ++i)
    {
	const int i0 = max (i - 1, 0);
	const int i1 = min (i + 1, n - 1);

	const Rgba &neighbor0 = rgbaIn[0][i0];
	const Rgba &neighbor1 = rgbaIn[0][i1];
	const Rgba &neighbor2 = rgbaIn[2][i0];
	const Rgba &neighbor3 = rgbaIn[2][i1];

	float sMean = min (1.0f, 0.25f * (saturation (neighbor0) +
					  saturation (neighbor1) +
					  saturation (neighbor2) +
					  saturation (neighbor3)));

	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