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annotate mupdf-source/thirdparty/leptonica/src/bilateral.h @ 2:b50eed0cc0ef upstream

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ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4. The directory name has changed: no version number in the expanded directory now.
author Franz Glasner <fzglas.hg@dom66.de>
date Mon, 15 Sep 2025 11:43:07 +0200
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1 /*====================================================================*
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2 - Copyright (C) 2001 Leptonica. All rights reserved.
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3 -
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4 - Redistribution and use in source and binary forms, with or without
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5 - modification, are permitted provided that the following conditions
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6 - are met:
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7 - 1. Redistributions of source code must retain the above copyright
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8 - notice, this list of conditions and the following disclaimer.
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9 - 2. Redistributions in binary form must reproduce the above
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10 - copyright notice, this list of conditions and the following
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11 - disclaimer in the documentation and/or other materials
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12 - provided with the distribution.
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13 -
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14 - THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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15 - ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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16 - LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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17 - A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL ANY
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18 - CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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19 - EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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20 - PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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21 - PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
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22 - OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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23 - NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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24 - SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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25 *====================================================================*/
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26
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27 #ifndef LEPTONICA_BILATERAL_H
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28 #define LEPTONICA_BILATERAL_H
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29
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30 /*!
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31 * \file bilateral.h
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32 *
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33 * <pre>
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34 * Contains the following struct
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35 * struct L_Bilateral
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36 *
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37 *
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38 * For a tutorial introduction to bilateral filters, which apply a
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39 * gaussian blur to smooth parts of the image while preserving edges, see
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40 * http://people.csail.mit.edu/sparis/bf_course/slides/03_definition_bf.pdf
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41 *
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42 * We give an implementation of a bilateral filtering algorithm given in:
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43 * "Real-Time O(1) Bilateral Filtering," by Yang, Tan and Ahuja, CVPR 2009
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44 * which is at:
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45 * http://vision.ai.uiuc.edu/~qyang6/publications/cvpr-09-qingxiong-yang.pdf
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46 * This is based on an earlier algorithm by Sylvain Paris and Frédo Durand:
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47 * http://people.csail.mit.edu/sparis/publi/2006/eccv/
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48 * Paris_06_Fast_Approximation.pdf
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49 *
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50 * The kernel of the filter is a product of a spatial gaussian and a
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51 * monotonically decreasing function of the difference in intensity
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52 * between the source pixel and the neighboring pixel. The intensity
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53 * part of the filter gives higher influence for pixels with intensities
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54 * that are near to the source pixel, and the spatial part of the
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55 * filter gives higher weight to pixels that are near the source pixel.
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56 * This combination smooths in relatively uniform regions, while
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57 * maintaining edges.
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58 *
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59 * The advantage of the appoach of Yang et al is that it is separable,
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60 * so the computation time is linear in the gaussian filter size.
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61 * Furthermore, it is possible to do much of the computation as a reduced
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62 * scale, which gives a good approximation to the full resolution version
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63 * but greatly speeds it up.
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64 *
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65 * The bilateral filtered value at x is:
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66 *
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67 * sum[y in N(x)]: spatial(|y - x|) * range(|I(x) - I(y)|) * I(y)
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68 * I'(x) = --------------------------------------------------------------
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69 * sum[y in N(x)]: spatial(|y - x|) * range(|I(x) - I(y)|)
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70 *
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71 * where I() is the input image, I'() is the filtered image, N(x) is the
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72 * set of pixels around x in the filter support, and spatial() and range()
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73 * are gaussian functions:
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74 * spatial(x) = exp(-x^2 / (2 * s_s^2))
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75 * range(x) = exp(-x^2 / (2 * s_r^2))
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76 * and s_s and s_r and the standard deviations of the two gaussians.
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77 *
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78 * Yang et al use a separable approximation to this, by defining a set
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79 * of related but separable functions J(k,x), that we call Principal
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80 * Bilateral Components (PBC):
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81 *
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82 * sum[y in N(x)]: spatial(|y - x|) * range(|k - I(y)|) * I(y)
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83 * J(k,x) = -----------------------------------------------------------
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84 * sum[y in N(x)]: spatial(|y - x|) * range(|k - I(y)|)
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85 *
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86 * which are computed quickly for a set of n values k[p], p = 0 ... n-1.
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87 * Then each output pixel is found using a linear interpolation:
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88 *
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89 * I'(x) = (1 - q) * J(k[p],x) + q * J(k[p+1],x)
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90 *
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91 * where J(k[p],x) and J(k[p+1],x) are PBC for which
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92 * k[p] <= I(x) and k[p+1] >= I(x), and
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93 * q = (I(x) - k[p]) / (k[p+1] - k[p]).
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94 *
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95 * We can also subsample I(x), create subsampled versions of J(k,x),
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96 * which are then interpolated between for I'(x).
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97 *
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98 * We generate 'pixsc', by optionally downscaling the input image
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99 * (using area mapping by the factor 'reduction'), and then adding
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100 * a mirrored border to avoid boundary cases. This is then used
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101 * to compute 'ncomps' PBCs.
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102 *
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103 * The 'spatial_stdev' is also downscaled by 'reduction'. The size
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104 * of the 'spatial' array is 4 * (reduced 'spatial_stdev') + 1.
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105 * The size of the 'range' array is 256.
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106 * </pre>
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107 */
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108
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109
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110 /*------------------------------------------------------------------------*
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111 * Bilateral filter *
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112 *------------------------------------------------------------------------*/
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113
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114 /*! Bilateral filter */
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115 struct L_Bilateral
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116 {
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117 struct Pix *pixs; /*!< clone of source pix */
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118 struct Pix *pixsc; /*!< downscaled pix with mirrored border */
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119 l_int32 reduction; /*!< 1, 2 or 4x for intermediates */
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120 l_float32 spatial_stdev; /*!< stdev of spatial gaussian */
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121 l_float32 range_stdev; /*!< stdev of range gaussian */
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122 l_float32 *spatial; /*!< 1D gaussian spatial kernel */
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123 l_float32 *range; /*!< one-sided gaussian range kernel */
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124 l_int32 minval; /*!< min value in 8 bpp pix */
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125 l_int32 maxval; /*!< max value in 8 bpp pix */
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126 l_int32 ncomps; /*!< number of intermediate results */
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127 l_int32 *nc; /*!< set of k values (size ncomps) */
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128 l_int32 *kindex; /*!< mapping from intensity to lower k */
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129 l_float32 *kfract; /*!< mapping from intensity to fract k */
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130 struct Pixa *pixac; /*!< intermediate result images (PBC) */
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131 l_uint32 ***lineset; /*!< lineptrs for pixac */
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132 };
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133 typedef struct L_Bilateral L_BILATERAL;
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134
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135
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136 #endif /* LEPTONICA_BILATERAL_H */