Mercurial > hgrepos > Python2 > PyMuPDF

annotate mupdf-source/thirdparty/libjpeg/wizard.txt @ 46:7ee69f120f19 default tip

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>>>>> tag v1.26.5+1 for changeset b74429b0f5c4
author Franz Glasner <fzglas.hg@dom66.de>
date Sat, 11 Oct 2025 17:17:30 +0200
parents b50eed0cc0ef
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 Advanced usage instructions for the Independent JPEG Group's JPEG software
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2 ==========================================================================
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4 This file describes cjpeg's "switches for wizards".
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6 The "wizard" switches are intended for experimentation with JPEG by persons
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7 who are reasonably knowledgeable about the JPEG standard. If you don't know
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8 what you are doing, DON'T USE THESE SWITCHES. You'll likely produce files
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9 with worse image quality and/or poorer compression than you'd get from the
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10 default settings. Furthermore, these switches must be used with caution
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11 when making files intended for general use, because not all JPEG decoders
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12 will support unusual JPEG parameter settings.
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15 Quantization Table Adjustment
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16 -----------------------------
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18 Ordinarily, cjpeg starts with a default set of tables (the same ones given
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19 as examples in the JPEG standard) and scales them up or down according to
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20 the -quality setting. The details of the scaling algorithm can be found in
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21 jcparam.c. At very low quality settings, some quantization table entries
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22 can get scaled up to values exceeding 255. Although 2-byte quantization
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23 values are supported by the IJG software, this feature is not in baseline
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24 JPEG and is not supported by all implementations. If you need to ensure
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25 wide compatibility of low-quality files, you can constrain the scaled
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26 quantization values to no more than 255 by giving the -baseline switch.
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27 Note that use of -baseline will result in poorer quality for the same file
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28 size, since more bits than necessary are expended on higher AC coefficients.
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30 You can substitute a different set of quantization values by using the
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31 -qtables switch:
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33 -qtables file Use the quantization tables given in the named file.
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35 The specified file should be a text file containing decimal quantization
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36 values. The file should contain one to four tables, each of 64 elements.
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37 The tables are implicitly numbered 0,1,etc. in order of appearance. Table
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38 entries appear in normal array order (NOT in the zigzag order in which they
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39 will be stored in the JPEG file).
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41 Quantization table files are free format, in that arbitrary whitespace can
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42 appear between numbers. Also, comments can be included: a comment starts
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43 with '#' and extends to the end of the line. Here is an example file that
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44 duplicates the default quantization tables:
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46 # Quantization tables given in JPEG spec, section K.1
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48 # This is table 0 (the luminance table):
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49 16 11 10 16 24 40 51 61
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50 12 12 14 19 26 58 60 55
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51 14 13 16 24 40 57 69 56
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52 14 17 22 29 51 87 80 62
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53 18 22 37 56 68 109 103 77
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54 24 35 55 64 81 104 113 92
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55 49 64 78 87 103 121 120 101
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56 72 92 95 98 112 100 103 99
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58 # This is table 1 (the chrominance table):
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59 17 18 24 47 99 99 99 99
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60 18 21 26 66 99 99 99 99
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61 24 26 56 99 99 99 99 99
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62 47 66 99 99 99 99 99 99
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63 99 99 99 99 99 99 99 99
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64 99 99 99 99 99 99 99 99
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65 99 99 99 99 99 99 99 99
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66 99 99 99 99 99 99 99 99
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68 If the -qtables switch is used without -quality, then the specified tables
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69 are used exactly as-is. If both -qtables and -quality are used, then the
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70 tables taken from the file are scaled in the same fashion that the default
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71 tables would be scaled for that quality setting. If -baseline appears, then
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72 the quantization values are constrained to the range 1-255.
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74 By default, cjpeg will use quantization table 0 for luminance components and
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75 table 1 for chrominance components. To override this choice, use the -qslots
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76 switch:
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78 -qslots N[,...] Select which quantization table to use for
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79 each color component.
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81 The -qslots switch specifies a quantization table number for each color
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82 component, in the order in which the components appear in the JPEG SOF marker.
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83 For example, to create a separate table for each of Y,Cb,Cr, you could
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84 provide a -qtables file that defines three quantization tables and say
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85 "-qslots 0,1,2". If -qslots gives fewer table numbers than there are color
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86 components, then the last table number is repeated as necessary.
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89 Sampling Factor Adjustment
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90 --------------------------
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91
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92 By default, cjpeg uses 2:1 horizontal and vertical downsampling when
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93 compressing YCbCr data, and no downsampling for all other color spaces.
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94 You can override this default with the -sample switch:
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96 -sample HxV[,...] Set JPEG sampling factors for each color
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97 component.
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98
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
99 The -sample switch specifies the JPEG sampling factors for each color
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
100 component, in the order in which they appear in the JPEG SOF marker.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
101 If you specify fewer HxV pairs than there are components, the remaining
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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102 components are set to 1x1 sampling. For example, the default YCbCr setting
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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103 is equivalent to "-sample 2x2,1x1,1x1", which can be abbreviated to
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
104 "-sample 2x2".
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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105
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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106 There are still some JPEG decoders in existence that support only 2x1
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
107 sampling (also called 4:2:2 sampling). Compatibility with such decoders can
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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108 be achieved by specifying "-sample 2x1". This is not recommended unless
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
109 really necessary, since it increases file size and encoding/decoding time
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
110 with very little quality gain.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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111
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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112
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
113 Multiple Scan / Progression Control
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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114 -----------------------------------
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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115
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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116 By default, cjpeg emits a single-scan sequential JPEG file. The
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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117 -progressive switch generates a progressive JPEG file using a default series
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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118 of progression parameters. You can create multiple-scan sequential JPEG
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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119 files or progressive JPEG files with custom progression parameters by using
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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120 the -scans switch:
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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121
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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122 -scans file Use the scan sequence given in the named file.
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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123
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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124 The specified file should be a text file containing a "scan script".
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
125 The script specifies the contents and ordering of the scans to be emitted.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
126 Each entry in the script defines one scan. A scan definition specifies
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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127 the components to be included in the scan, and for progressive JPEG it also
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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128 specifies the progression parameters Ss,Se,Ah,Al for the scan. Scan
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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129 definitions are separated by semicolons (';'). A semicolon after the last
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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130 scan definition is optional.
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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131
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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132 Each scan definition contains one to four component indexes, optionally
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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133 followed by a colon (':') and the four progressive-JPEG parameters. The
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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134 component indexes denote which color component(s) are to be transmitted in
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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135 the scan. Components are numbered in the order in which they appear in the
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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136 JPEG SOF marker, with the first component being numbered 0. (Note that these
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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137 indexes are not the "component ID" codes assigned to the components, just
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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138 positional indexes.)
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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139
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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140 The progression parameters for each scan are:
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
141 Ss Zigzag index of first coefficient included in scan
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
142 Se Zigzag index of last coefficient included in scan
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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143 Ah Zero for first scan of a coefficient, else Al of prior scan
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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144 Al Successive approximation low bit position for scan
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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145 If the progression parameters are omitted, the values 0,63,0,0 are used,
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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146 producing a sequential JPEG file. cjpeg automatically determines whether
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
147 the script represents a progressive or sequential file, by observing whether
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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148 Ss and Se values other than 0 and 63 appear. (The -progressive switch is
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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149 not needed to specify this; in fact, it is ignored when -scans appears.)
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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150 The scan script must meet the JPEG restrictions on progression sequences.
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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151 (cjpeg checks that the spec's requirements are obeyed.)
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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152
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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153 Scan script files are free format, in that arbitrary whitespace can appear
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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154 between numbers and around punctuation. Also, comments can be included: a
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
155 comment starts with '#' and extends to the end of the line. For additional
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
156 legibility, commas or dashes can be placed between values. (Actually, any
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
157 single punctuation character other than ':' or ';' can be inserted.) For
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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158 example, the following two scan definitions are equivalent:
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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159 0 1 2: 0 63 0 0;
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
160 0,1,2 : 0-63, 0,0 ;
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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161
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
162 Here is an example of a scan script that generates a partially interleaved
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
163 sequential JPEG file:
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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164
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
165 0; # Y only in first scan
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
166 1 2; # Cb and Cr in second scan
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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167
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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168 Here is an example of a progressive scan script using only spectral selection
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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169 (no successive approximation):
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Franz Glasner <fzglas.hg@dom66.de>
parents:
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170
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
171 # Interleaved DC scan for Y,Cb,Cr:
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
172 0,1,2: 0-0, 0, 0 ;
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
173 # AC scans:
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
174 0: 1-2, 0, 0 ; # First two Y AC coefficients
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
175 0: 3-5, 0, 0 ; # Three more
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
176 1: 1-63, 0, 0 ; # All AC coefficients for Cb
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
177 2: 1-63, 0, 0 ; # All AC coefficients for Cr
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
178 0: 6-9, 0, 0 ; # More Y coefficients
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
179 0: 10-63, 0, 0 ; # Remaining Y coefficients
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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180
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
181 Here is an example of a successive-approximation script. This is equivalent
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
182 to the default script used by "cjpeg -progressive" for YCbCr images:
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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183
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
184 # Initial DC scan for Y,Cb,Cr (lowest bit not sent)
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
185 0,1,2: 0-0, 0, 1 ;
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
186 # First AC scan: send first 5 Y AC coefficients, minus 2 lowest bits:
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
187 0: 1-5, 0, 2 ;
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
188 # Send all Cr,Cb AC coefficients, minus lowest bit:
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
189 # (chroma data is usually too small to be worth subdividing further;
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
190 # but note we send Cr first since eye is least sensitive to Cb)
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
191 2: 1-63, 0, 1 ;
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
192 1: 1-63, 0, 1 ;
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
193 # Send remaining Y AC coefficients, minus 2 lowest bits:
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
194 0: 6-63, 0, 2 ;
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
195 # Send next-to-lowest bit of all Y AC coefficients:
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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196 0: 1-63, 2, 1 ;
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197 # At this point we've sent all but the lowest bit of all coefficients.
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198 # Send lowest bit of DC coefficients
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199 0,1,2: 0-0, 1, 0 ;
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200 # Send lowest bit of AC coefficients
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201 2: 1-63, 1, 0 ;
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202 1: 1-63, 1, 0 ;
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203 # Y AC lowest bit scan is last; it's usually the largest scan
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204 0: 1-63, 1, 0 ;
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205
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206 It may be worth pointing out that this script is tuned for quality settings
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207 of around 50 to 75. For lower quality settings, you'd probably want to use
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208 a script with fewer stages of successive approximation (otherwise the
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209 initial scans will be really bad). For higher quality settings, you might
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210 want to use more stages of successive approximation (so that the initial
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211 scans are not too large).