source: NonGTP/OpenEXR/include/IlmImf/ImfRgbaYca.h @ 855

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[855]1#ifndef INCLUDED_IMF_RGBA_YCA_H
2#define INCLUDED_IMF_RGBA_YCA_H
3
4//////////////////////////////////////////////////////////////////////////////
5//
6// Copyright (c) 2004, Industrial Light & Magic, a division of Lucasfilm
7// Entertainment Company Ltd.  Portions contributed and copyright held by
8// others as indicated.  All rights reserved.
9//
10// Redistribution and use in source and binary forms, with or without
11// modification, are permitted provided that the following conditions are
12// met:
13//
14//     * Redistributions of source code must retain the above
15//       copyright notice, this list of conditions and the following
16//       disclaimer.
17//
18//     * Redistributions in binary form must reproduce the above
19//       copyright notice, this list of conditions and the following
20//       disclaimer in the documentation and/or other materials provided with
21//       the distribution.
22//
23//     * Neither the name of Industrial Light & Magic nor the names of
24//       any other contributors to this software may be used to endorse or
25//       promote products derived from this software without specific prior
26//       written permission.
27//
28// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
29// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
30// THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
31// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
32// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
33// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
34// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
35// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
36// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
37// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
38// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
39//
40//////////////////////////////////////////////////////////////////////////////
41
42//-----------------------------------------------------------------------------
43//
44//      Conversion between RGBA (red, green, blue alpha)
45//      and YCA (luminance, subsampled chroma, alpha) data:
46//
47//      Luminance, Y, is computed as a weighted sum of R, G, and B:
48//
49//              Y = yw.x * R + yw.y * G + yw.z * B
50//
51//      Function computeYw() computes a set of RGB-to-Y weights, yw,
52//      from a set of primary and white point chromaticities.
53//
54//      Chroma, C, consists of two components, RY and BY:
55//
56//              RY = (R - Y) / Y
57//              BY = (B - Y) / Y
58//
59//      For efficiency, the x and y subsampling rates for chroma are
60//      hardwired to 2, and the chroma subsampling and reconstruction
61//      filters are fixed 27-pixel wide windowed sinc functions.
62//
63//      Starting with an image that has RGBA data for all pixels,
64//
65//              RGBA RGBA RGBA RGBA ... RGBA RGBA
66//              RGBA RGBA RGBA RGBA ... RGBA RGBA
67//              RGBA RGBA RGBA RGBA ... RGBA RGBA
68//              RGBA RGBA RGBA RGBA ... RGBA RGBA
69//              ...
70//              RGBA RGBA RGBA RGBA ... RGBA RGBA
71//              RGBA RGBA RGBA RGBA ... RGBA RGBA
72//
73//      function RGBAtoYCA() converts the pixels to YCA format:
74//
75//              YCA  YCA  YCA  YCA  ... YCA  YCA
76//              YCA  YCA  YCA  YCA  ... YCA  YCA
77//              YCA  YCA  YCA  YCA  ... YCA  YCA
78//              YCA  YCA  YCA  YCA  ... YCA  YCA
79//              ...
80//              YCA  YCA  YCA  YCA  ... YCA  YCA
81//              YCA  YCA  YCA  YCA  ... YCA  YCA
82//
83//      Next, decimateChomaHoriz() eliminates the chroma values from
84//      the odd-numbered pixels in every scan line:
85//
86//              YCA  YA   YCA  YA   ... YCA  YA 
87//              YCA  YA   YCA  YA   ... YCA  YA 
88//              YCA  YA   YCA  YA   ... YCA  YA 
89//              YCA  YA   YCA  YA   ... YCA  YA 
90//              ...
91//              YCA  YA   YCA  YA   ... YCA  YA 
92//              YCA  YA   YCA  YA   ... YCA  YA 
93//
94//      decimateChromaVert() eliminates all chroma values from the
95//      odd-numbered scan lines:
96//
97//              YCA  YA   YCA  YA   ... YCA  YA 
98//              YA   YA   YA   YA   ... YA   YA 
99//              YCA  YA   YCA  YA   ... YCA  YA 
100//              YA   YA   YA   YA   ... YA   YA 
101//              ...
102//              YCA  YA   YCA  YA   ... YCA  YA 
103//              YA   YA   YA   YA   ... YA   YA 
104//
105//      Finally, roundYCA() reduces the precision of the luminance
106//      and chroma values so that the pixel data shrink more when
107//      they are saved in a compressed file.
108//
109//      The output of roundYCA() can be converted back to a set
110//      of RGBA pixel data that is visually very similar to the
111//      original RGBA image, by calling reconstructChromaHoriz(),
112//      reconstructChromaVert(), YCAtoRGBA(), and finally
113//      fixSaturation().
114//
115//-----------------------------------------------------------------------------
116
117#include <ImfRgba.h>
118#include <ImfChromaticities.h>
119
120namespace Imf {
121namespace RgbaYca {
122
123
124//
125// Width of the chroma subsampling and reconstruction filters
126//
127
128static const int N = 27;
129static const int N2 = N / 2;
130
131
132//
133// Convert a set of primary chromaticities into a set of weighting
134// factors for computing a pixels's luminance, Y, from R, G and B
135//
136
137Imath::V3f computeYw (const Chromaticities &cr);
138
139
140//
141// Convert an array of n RGBA pixels, rgbaIn, to YCA (luminance/chroma/alpha):
142//
143//      ycaOut[i].g = Y (rgbaIn[i]);
144//      ycaOut[i].r = RY (rgbaIn[i]);
145//      ycaOut[i].b = BY (rgbaIn[i]);
146//      ycaOut[i].a = aIsValid? rgbaIn[i].a: 1
147//
148// yw is a set of RGB-to-Y weighting factors, as computed by computeYw().
149//
150
151void RGBAtoYCA (const Imath::V3f &yw,
152                int n,
153                bool aIsValid,
154                const Rgba rgbaIn[/*n*/],
155                Rgba ycaOut[/*n*/]);
156
157//
158// Perform horizontal low-pass filtering and subsampling of
159// the chroma channels of an array of n pixels.  In order
160// to avoid indexing off the ends of the input array during
161// low-pass filtering, ycaIn must have N2 extra pixels at
162// both ends.  Before calling decimateChromaHoriz(), the extra
163// pixels should be filled with copies of the first and last
164// "real" input pixel.
165//
166
167void decimateChromaHoriz (int n,
168                          const Rgba ycaIn[/*n+N-1*/],
169                          Rgba ycaOut[/*n*/]);
170
171//
172// Perform vertical chroma channel low-pass filtering and subsampling.
173// N scan lines of input pixels are combined into a single scan line
174// of output pixels.
175//
176
177void decimateChromaVert (int n,
178                         const Rgba * const ycaIn[N],
179                         Rgba ycaOut[/*n*/]);
180
181//
182// Round the luminance and chroma channels of an array of YCA
183// pixels that has already been filtered and subsampled.
184// The signifcands of the pixels' luminance and chroma values
185// are rounded to roundY and roundC bits respectively.
186//
187
188void roundYCA (int n,
189               unsigned int roundY,
190               unsigned int roundC,
191               const Rgba ycaIn[/*n*/],
192               Rgba ycaOut[/*n*/]);
193
194//
195// For a scan line that has valid chroma data only for every other pixel,
196// reconstruct the missing chroma values.
197//
198
199void reconstructChromaHoriz (int n,
200                             const Rgba ycaIn[/*n+N-1*/],
201                             Rgba ycaOut[/*n*/]);
202
203//
204// For a scan line that has only luminance and no valid chroma data,
205// reconstruct chroma from the surronding N scan lines.
206//
207
208void reconstructChromaVert (int n,
209                            const Rgba * const ycaIn[N],
210                            Rgba ycaOut[/*n*/]);
211                         
212//
213// Convert an array of n YCA (luminance/chroma/alpha) pixels to RGBA.
214// This function is the inverse of RGBAtoYCA().
215// yw is a set of RGB-to-Y weighting factors, as computed by computeYw().
216//
217
218void YCAtoRGBA (const Imath::V3f &yw,
219                int n,
220                const Rgba ycaIn[/*n*/],
221                Rgba rgbaOut[/*n*/]);
222                         
223//
224// Eliminate super-saturated pixels:
225//
226// Converting an image from RGBA to YCA, low-pass filtering chroma,
227// and converting the result back to RGBA can produce pixels with
228// super-saturated colors, where one or two of the RGB components
229// become zero or negative.  (The low-pass and reconstruction filters
230// introduce some amount of ringing into the chroma components.
231// This can lead to negative RGB values near high-contrast edges.)
232//
233// The fixSaturation() function finds super-saturated pixels and
234// corrects them by desaturating their colors while maintaining
235// their luminance.  fixSaturation() takes three adjacent input
236// scan lines, rgbaIn[0], rgbaIn[1], rgbaIn[2], adjusts the
237// saturation of rgbaIn[1], and stores the result in rgbaOut.
238//
239
240void fixSaturation (const Imath::V3f &yw,
241                    int n,
242                    const Rgba * const rgbaIn[3],
243                    Rgba rgbaOut[/*n*/]);
244
245} // namespace RgbaYca
246} // namespace Imf
247
248#endif
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