1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 3.. _yuv-formats: 4 5*********** 6YUV Formats 7*********** 8 9YUV is the format native to TV broadcast and composite video signals. It 10separates the brightness information (Y) from the color information (U 11and V or Cb and Cr). The color information consists of red and blue 12*color difference* signals, this way the green component can be 13reconstructed by subtracting from the brightness component. See 14:ref:`colorspaces` for conversion examples. YUV was chosen because 15early television would only transmit brightness information. To add 16color in a way compatible with existing receivers a new signal carrier 17was added to transmit the color difference signals. 18 19 20Subsampling 21=========== 22 23YUV formats commonly encode images with a lower resolution for the chroma 24components than for the luma component. This compression technique, taking 25advantage of the human eye being more sensitive to luminance than color 26differences, is called chroma subsampling. 27 28While many combinations of subsampling factors in the horizontal and vertical 29direction are possible, common factors are 1 (no subsampling), 2 and 4, with 30horizontal subsampling always larger than or equal to vertical subsampling. 31Common combinations are named as follows. 32 33- `4:4:4`: No subsampling 34- `4:2:2`: Horizontal subsampling by 2, no vertical subsampling 35- `4:2:0`: Horizontal subsampling by 2, vertical subsampling by 2 36- `4:1:1`: Horizontal subsampling by 4, no vertical subsampling 37- `4:1:0`: Horizontal subsampling by 4, vertical subsampling by 4 38 39Subsampling the chroma component effectively creates chroma values that can be 40located in different spatial locations: 41 42- .. _yuv-chroma-centered: 43 44 The subsampled chroma value may be calculated by simply averaging the chroma 45 value of two consecutive pixels. It effectively models the chroma of a pixel 46 sited between the two original pixels. This is referred to as centered or 47 interstitially sited chroma. 48 49- .. _yuv-chroma-cosited: 50 51 The other option is to subsample chroma values in a way that place them in 52 the same spatial sites as the pixels. This may be performed by skipping every 53 other chroma sample (creating aliasing artifacts), or with filters using an 54 odd number of taps. This is referred to as co-sited chroma. 55 56The following examples show different combination of chroma siting in a 4x4 57image. 58 59.. flat-table:: 4:2:2 subsampling, interstitially sited 60 :header-rows: 1 61 :stub-columns: 1 62 63 * - 64 - 0 65 - 66 - 1 67 - 68 - 2 69 - 70 - 3 71 * - 0 72 - Y 73 - C 74 - Y 75 - 76 - Y 77 - C 78 - Y 79 * - 1 80 - Y 81 - C 82 - Y 83 - 84 - Y 85 - C 86 - Y 87 * - 2 88 - Y 89 - C 90 - Y 91 - 92 - Y 93 - C 94 - Y 95 * - 3 96 - Y 97 - C 98 - Y 99 - 100 - Y 101 - C 102 - Y 103 104.. flat-table:: 4:2:2 subsampling, co-sited 105 :header-rows: 1 106 :stub-columns: 1 107 108 * - 109 - 0 110 - 111 - 1 112 - 113 - 2 114 - 115 - 3 116 * - 0 117 - Y/C 118 - 119 - Y 120 - 121 - Y/C 122 - 123 - Y 124 * - 1 125 - Y/C 126 - 127 - Y 128 - 129 - Y/C 130 - 131 - Y 132 * - 2 133 - Y/C 134 - 135 - Y 136 - 137 - Y/C 138 - 139 - Y 140 * - 3 141 - Y/C 142 - 143 - Y 144 - 145 - Y/C 146 - 147 - Y 148 149.. flat-table:: 4:2:0 subsampling, horizontally interstitially sited, vertically co-sited 150 :header-rows: 1 151 :stub-columns: 1 152 153 * - 154 - 0 155 - 156 - 1 157 - 158 - 2 159 - 160 - 3 161 * - 0 162 - Y 163 - C 164 - Y 165 - 166 - Y 167 - C 168 - Y 169 * - 1 170 - Y 171 - 172 - Y 173 - 174 - Y 175 - 176 - Y 177 * - 2 178 - Y 179 - C 180 - Y 181 - 182 - Y 183 - C 184 - Y 185 * - 3 186 - Y 187 - 188 - Y 189 - 190 - Y 191 - 192 - Y 193 194.. flat-table:: 4:1:0 subsampling, horizontally and vertically interstitially sited 195 :header-rows: 1 196 :stub-columns: 1 197 198 * - 199 - 0 200 - 201 - 1 202 - 203 - 2 204 - 205 - 3 206 * - 0 207 - Y 208 - 209 - Y 210 - 211 - Y 212 - 213 - Y 214 * - 215 - 216 - 217 - 218 - 219 - 220 - 221 - 222 * - 1 223 - Y 224 - 225 - Y 226 - 227 - Y 228 - 229 - Y 230 * - 231 - 232 - 233 - 234 - C 235 - 236 - 237 - 238 * - 2 239 - Y 240 - 241 - Y 242 - 243 - Y 244 - 245 - Y 246 * - 247 - 248 - 249 - 250 - 251 - 252 - 253 - 254 * - 3 255 - Y 256 - 257 - Y 258 - 259 - Y 260 - 261 - Y 262 263 264.. toctree:: 265 :maxdepth: 1 266 267 pixfmt-packed-yuv 268 pixfmt-yuv-planar 269 pixfmt-yuv-luma 270 pixfmt-y8i 271 pixfmt-y12i 272 pixfmt-uv8 273 pixfmt-m420 274