136 lines
4.4 KiB
C++
136 lines
4.4 KiB
C++
///////////////////////////////////////////////////////////////////////////
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//
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// Copyright (c) 2003, Industrial Light & Magic, a division of Lucas
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// Digital Ltd. LLC
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//
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Industrial Light & Magic nor the names of
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// its contributors may be used to endorse or promote products derived
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// from this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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//
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///////////////////////////////////////////////////////////////////////////
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//-----------------------------------------------------------------------------
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//
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// CIE (x,y) chromaticities, and conversions between
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// RGB tiples and CIE XYZ tristimulus values.
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//
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//-----------------------------------------------------------------------------
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#include <ImfChromaticities.h>
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namespace Imf {
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Chromaticities::Chromaticities (const Imath::V2f &red,
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const Imath::V2f &green,
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const Imath::V2f &blue,
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const Imath::V2f &white)
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:
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red (red),
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green (green),
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blue (blue),
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white (white)
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{
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// empty
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}
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Imath::M44f
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RGBtoXYZ (const Chromaticities chroma, float Y)
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{
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//
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// For an explanation of how the color conversion matrix is derived,
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// see Roy Hall, "Illumination and Color in Computer Generated Imagery",
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// Springer-Verlag, 1989, chapter 3, "Perceptual Response"; and
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// Charles A. Poynton, "A Technical Introduction to Digital Video",
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// John Wiley & Sons, 1996, chapter 7, "Color science for video".
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//
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//
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// X and Z values of RGB value (1, 1, 1), or "white"
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//
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float X = chroma.white.x * Y / chroma.white.y;
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float Z = (1 - chroma.white.x - chroma.white.y) * Y / chroma.white.y;
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//
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// Scale factors for matrix rows
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//
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float d = chroma.red.x * (chroma.blue.y - chroma.green.y) +
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chroma.blue.x * (chroma.green.y - chroma.red.y) +
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chroma.green.x * (chroma.red.y - chroma.blue.y);
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float Sr = (X * (chroma.blue.y - chroma.green.y) -
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chroma.green.x * (Y * (chroma.blue.y - 1) +
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chroma.blue.y * (X + Z)) +
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chroma.blue.x * (Y * (chroma.green.y - 1) +
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chroma.green.y * (X + Z))) / d;
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float Sg = (X * (chroma.red.y - chroma.blue.y) +
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chroma.red.x * (Y * (chroma.blue.y - 1) +
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chroma.blue.y * (X + Z)) -
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chroma.blue.x * (Y * (chroma.red.y - 1) +
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chroma.red.y * (X + Z))) / d;
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float Sb = (X * (chroma.green.y - chroma.red.y) -
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chroma.red.x * (Y * (chroma.green.y - 1) +
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chroma.green.y * (X + Z)) +
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chroma.green.x * (Y * (chroma.red.y - 1) +
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chroma.red.y * (X + Z))) / d;
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//
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// Assemble the matrix
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//
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Imath::M44f M;
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M[0][0] = Sr * chroma.red.x;
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M[0][1] = Sr * chroma.red.y;
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M[0][2] = Sr * (1 - chroma.red.x - chroma.red.y);
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M[1][0] = Sg * chroma.green.x;
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M[1][1] = Sg * chroma.green.y;
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M[1][2] = Sg * (1 - chroma.green.x - chroma.green.y);
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M[2][0] = Sb * chroma.blue.x;
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M[2][1] = Sb * chroma.blue.y;
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M[2][2] = Sb * (1 - chroma.blue.x - chroma.blue.y);
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return M;
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}
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Imath::M44f
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XYZtoRGB (const Chromaticities chroma, float Y)
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{
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return RGBtoXYZ (chroma, Y).inverse();
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}
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} // namespace Imf
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