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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 | .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later .. _yuv-formats: *********** YUV Formats *********** YUV is the format native to TV broadcast and composite video signals. It separates the brightness information (Y) from the color information (U and V or Cb and Cr). The color information consists of red and blue *color difference* signals, this way the green component can be reconstructed by subtracting from the brightness component. See :ref:`colorspaces` for conversion examples. YUV was chosen because early television would only transmit brightness information. To add color in a way compatible with existing receivers a new signal carrier was added to transmit the color difference signals. Subsampling =========== YUV formats commonly encode images with a lower resolution for the chroma components than for the luma component. This compression technique, taking advantage of the human eye being more sensitive to luminance than color differences, is called chroma subsampling. While many combinations of subsampling factors in the horizontal and vertical direction are possible, common factors are 1 (no subsampling), 2 and 4, with horizontal subsampling always larger than or equal to vertical subsampling. Common combinations are named as follows. - `4:4:4`: No subsampling - `4:2:2`: Horizontal subsampling by 2, no vertical subsampling - `4:2:0`: Horizontal subsampling by 2, vertical subsampling by 2 - `4:1:1`: Horizontal subsampling by 4, no vertical subsampling - `4:1:0`: Horizontal subsampling by 4, vertical subsampling by 4 Subsampling the chroma component effectively creates chroma values that can be located in different spatial locations: - .. _yuv-chroma-centered: The subsampled chroma value may be calculated by simply averaging the chroma value of two consecutive pixels. It effectively models the chroma of a pixel sited between the two original pixels. This is referred to as centered or interstitially sited chroma. - .. _yuv-chroma-cosited: The other option is to subsample chroma values in a way that place them in the same spatial sites as the pixels. This may be performed by skipping every other chroma sample (creating aliasing artifacts), or with filters using an odd number of taps. This is referred to as co-sited chroma. The following examples show different combination of chroma siting in a 4x4 image. .. flat-table:: 4:2:2 subsampling, interstitially sited :header-rows: 1 :stub-columns: 1 * - - 0 - - 1 - - 2 - - 3 * - 0 - Y - C - Y - - Y - C - Y * - 1 - Y - C - Y - - Y - C - Y * - 2 - Y - C - Y - - Y - C - Y * - 3 - Y - C - Y - - Y - C - Y .. flat-table:: 4:2:2 subsampling, co-sited :header-rows: 1 :stub-columns: 1 * - - 0 - - 1 - - 2 - - 3 * - 0 - Y/C - - Y - - Y/C - - Y * - 1 - Y/C - - Y - - Y/C - - Y * - 2 - Y/C - - Y - - Y/C - - Y * - 3 - Y/C - - Y - - Y/C - - Y .. flat-table:: 4:2:0 subsampling, horizontally interstitially sited, vertically co-sited :header-rows: 1 :stub-columns: 1 * - - 0 - - 1 - - 2 - - 3 * - 0 - Y - C - Y - - Y - C - Y * - 1 - Y - - Y - - Y - - Y * - 2 - Y - C - Y - - Y - C - Y * - 3 - Y - - Y - - Y - - Y .. flat-table:: 4:1:0 subsampling, horizontally and vertically interstitially sited :header-rows: 1 :stub-columns: 1 * - - 0 - - 1 - - 2 - - 3 * - 0 - Y - - Y - - Y - - Y * - - - - - - - - * - 1 - Y - - Y - - Y - - Y * - - - - - C - - - * - 2 - Y - - Y - - Y - - Y * - - - - - - - - * - 3 - Y - - Y - - Y - - Y .. toctree:: :maxdepth: 1 pixfmt-packed-yuv pixfmt-yuv-planar pixfmt-yuv-luma pixfmt-y8i pixfmt-y12i pixfmt-uv8 pixfmt-m420 |