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1 BPG Image library and utilities
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2 -------------------------------
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3
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4 1) Quick introduction
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5 ---------------------
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6
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7 - Edit the Makefile to change the compile options (the default compile
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8 options should be OK for Linux). Type 'make' to compile and 'make
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9 install' to install the compiled binaries.
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10
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11 - bpgview: in order to compile it you need to install the SDL and
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12 SDL_image libraries.
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13
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14 - Emscripten usage: in order to generate the Javascript decoder, you
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15 must install Emscripten and enable its use in the Makefile.
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16
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17 - An HTML demonstration (with a precompiled Javascript decoder) is
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18 available in html/index.html (if you use Chrome and want to use
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19 file:// to access it, launch Chrome with the option
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20 --allow-file-access-from-files).
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21
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22 - The BPG file format is specified in doc/bpg_spec.txt.
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23
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24 2) Compilation and Installation Notes
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25 -------------------------------------
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26
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27 2.1) Linux
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28 ----------
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29
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30 - Edit the Makefile to change the compile options (the default
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31 compile options should be OK). Type 'make' to compile and 'make
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32 install' to install the compiled binaries.
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33
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34 - Use 'make -j N' where N is the number of CPU cores to compile faster.
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35
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36 - The following packages must be installed: SDL-devel
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37 SDL_image-devel yasm. It is recommended to use yasm version >= 1.3.0
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38 to have a faster compilation.
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39
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40 - Only a 64 bit target is supported because x265 needs it for bit
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41 depths > 8.
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42
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43 2.2) Windows
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44 ------------
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45
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46 - Only cross-compilation from Linux is supported.
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47
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48 - The following packages need to be installed: mingw64-gcc
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49 mingw64-libpng mingw64-libjpeg-turbo mingw64-SDL mingw64-SDL_image
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50 yasm. It is recommended to use yasm version >= 1.3.0 to have a
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51 faster compilation.
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52
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53 - Only a 64 bit target is supported because x265 needs it for bit
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54 depths > 8.
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55
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56 3) BPG encoder
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57 --------------
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58
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59 The BPG command line encoder is 'bpgenc'. It takes JPEG or PNG images
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60 as input.
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61
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62 - Speed: by default bpgenc uses the x265. You can compile the much
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63 slower but more efficient JCTVC encoder and select it with the '-e
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64 jctvc' option. With x265 you can select the encoding speed with the
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65 '-m' option (1 = fast, but larger image, 9 = slower but smaller
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66 image).
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67
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68 - Bit depth: the default bit depth is 8. You can increase it to 10
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69 ('-b 10' option) to slightly increase the compression ratio. For web
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70 publishing it is generally not a good idea because the Javascript
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71 decoder uses more memory. The compiled x265 encoder supports the bit
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72 depth of 8, 10 and 12. The slower JCTVC encoder can be compiled to
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73 support higher bit depths (up to 14) by enabling the Makefile
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74 define: USE_JCTVC_HIGH_BIT_DEPTH.
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75
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76 - Lossless compression is supported as a bonus thru the HEVC lossless
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77 capabilities. Use a PNG input in this case unless you know what you
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78 do ! In case of a JPEG input, the compression is lossless related to
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79 the JPEG YCbCr data, not the RGB data. In any case, the bit depth
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80 should match the one of your picture otherwise the file size
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81 increases a lot. By default the lossless mode sets the bit depth to
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82 8 bits. The prefered color space is set to "rgb". Notes:
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83
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84 - lossless mode is less tested that the lossy mode but it usually
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85 gives better results that PNG on photographic images.
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86
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87 - the JCTVC encoder gives smaller images than the x265 encoder
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88 with lossless compression.
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89
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90 - There is a small difference of interpretation of the quantizer
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91 parameter (-q option) between the x265 and JCTVC encoder.
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92
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93 - Color space and chroma format:
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94
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95 * For JPEG input, the color space of the input image is not
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96 modified (it is YCbCr, RGB, YCbCrK or CMYK). The chroma is
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97 subsampled according to the preferred chroma format ('-f'
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98 option).
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99
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100 * For PNG input, the input image is converted to the preferred
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101 color space ('-c' option). Its chroma is then subsampled
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102 according to the preferred chroma format.
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103
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104 * grayscale images are kept unmodified.
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105
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106 - Premultiplied alpha: by default bpgenc uses non-premultiplied alpha
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107 to preserve the color components. However, premultiplied alpha
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108 ('-premul' option) usually gives a better compression at the expense
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109 of a loss in the color components. This loss is not an issue if the
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110 image is not edited.
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111
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112 - Animations: with the '-a' option, animations can be encoded from a
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113 sequence of PNG or JPEG images, indexed from 1 or 0. For example:
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114
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115 ./bpgenc -a anim%2d.png -fps 25 -loop 0 -o anim.bpg
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116
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117 generates an animation from anim01.png, anim02.png, etc... The frame
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118 rate is specified with '-fps' and the number of loops with '-loop'
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119 (0 = infinite). If a different delay per image is needed as in some
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120 animated GIFs, a text file can be specified with the '-delayfile'
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121 option. It contains one number per image giving its duration in
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122 centiseconds. All durations are rounded to a multiple of '1/fps', so
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123 it is important to set a consistent frame rate.
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124
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125 The necessary frames and delay file can be generated from animated
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126 GIFs with the ImageMagick tools:
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127
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128 convert -coalesce anim.gif anim%d.png
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129
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130 identify -format "%T\n" anim.gif > anim.txt
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131
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132 In order to reduce the file size, the frame rate can be choosen so
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133 that most frames have a frame period of 1 (hence if anim.txt
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134 contains only frame durations of 5 centiseconds, then choose a frame
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135 rate of 20 frames/s).
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136
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137 As GIFs use paletted colors and 1 bit transparency, it is always
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138 better to start from the source material (e.g. PNG files) to have
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139 the best quality.
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140
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141 A BPG decoder not supporting animations only displays the first
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142 frame.
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143
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144 - By default, bpgenc does not copy the metadata. You can copy them
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145 with the '-keepmetadata' option. For JPEG input, EXIF, ICCP and XMP
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146 are copied. For PNG input, ICCP is copied.
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147
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148 - Objective comparisons: x265 is tuned by default for SSIM. the JCTVC
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149 encoder is tuned for PSNR only, not for SSIM, so you should use PSNR
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150 when making objective comparison with other formats.
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151
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152 4) BPG decoder
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153 --------------
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154
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155 The BPG command line decoder is bpgdec. It outputs a PNG or PPM
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156 image. Use a PPM output to get the fastest speed.
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157
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158 - With the '-i' option, you have information about the BPG image (and
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159 no decoded image is output).
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160
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161 - The '-b' option selects the bit depth (8 or 16) of the PNG
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162 output. It is independent of the internal BPG bit depth.
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163
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164 5) BPG viewer
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165 -------------
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166
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167 The BPG image viewer uses the SDL library to display BPG images and
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168 other image formats supported by the SDL_image library. The available
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169 keys are displayed by launching bpgview without parameters. bpgview
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170 supports BPG animations.
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171
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172 6) BPG decoding library
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173 -----------------------
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174
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175 BPG images can be decoded in any program with the libbpg
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176 library.
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177
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178 The API is not considered stable yet so that the library is only
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179 provided as a static one.
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180
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181 Currently there is no similar library for encoding so you should
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182 invoke the bpgenc utility.
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183
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184 7) Javascript decoder
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185 ---------------------
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186
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187 The following Javascript decoders are available, sorted by increasing size:
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188
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189 > 8 bits animations
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190 bpgdec8.js no no
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191 bpgdec.js yes no
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192 bpgdec8a.js no yes
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193
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194
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195 The 8 bit only decoders are a little faster and consumes less memory
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196 (16 MB instead of 32 MB by default, you can change the memory
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197 configuration in the Makefile if you want to handle larger images).
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198
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199 The Javascript decoder substitutes all the <img> tags with a source
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200 having a .bpg extension with a <canvas> tag and decodes the BPG image
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201 into it. Stylesheets are supported (the 'id' and 'class' attributes
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202 are preserved). The 'width' and 'height' attributes are supported only
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203 with pixel units.
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204
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205 The image data is downloaded with the XMLHttpRequest object. So the
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206 BPG images and the BPG Javascript decoder must be in the same domain
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207 unless Cross-Origin Resource Sharing is used.
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208
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209 When animations are displayed, all the frames are stored in memory, so
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210 animations with a large number of frames and large resolutions should
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211 be avoided, as with animated GIFs.
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212
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213 asm.js gives an interesting speed boost, so we hope that more browsers
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214 will support this Javascript subset.
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215
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216 8) FFmpeg modifications
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217 -----------------------
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218
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219 - Completed support of chroma_format_idc = 0 (monochrome mode).
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220
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221 - Fixed RDPCM support (intra predictions).
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222
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223 - Reduced memory usage for the SAO loop filter.
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224
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225 - Generated the IDCT coefficients dynamically to reduce the code size.
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226
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227 - Added a 'dynamic bit depth' mode where all the bit depths from 8 to
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228 14 are supported without code duplication but slower decoding.
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229
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230 - Added a modified SPS header to reduce the size of the BPG decoder
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231 (an alternate solution is to generate standard VPS and SPS headers
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232 from the BPG header).
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233
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234 - Added defines to keep only the HEVC intra code and suppress the
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235 parsing of all the irrelevant NAL units.
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236
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237 - Stripped FFmpeg from all codecs except HEVC and the necessary
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238 support code.
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239
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240 9) x265 modifications
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241 ---------------------
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242
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243 - Support of monochrome format (some parts not used by BPG may be
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244 missing).
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245
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246 - Support of static build.
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247
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248 10) Licensing
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249 -------------
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250
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251 - libbpg and bpgdec are released under the LGPL license (the FFmpeg
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252 part is under the LGPL, the BPG specific part is released under the
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253 BSD license).
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254
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255 - bpgenc is released under the GPL version 2 license. The BPG specific
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256 code is released under the BSD license. The JCTVC code is released
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257 under the BSD license. The x265 code is released under the GPL
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258 version 2 license.
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259
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260 - BPG relies on the HEVC compression technology which may be protected
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261 by patents in some countries. Most devices already include or will
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262 include hardware HEVC support, so we suggest to use it if patents
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263 are an issue.
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