1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _yuv-formats: 5 6*********** 7YUV Formats 8*********** 9 10YUV is the format native to TV broadcast and composite video signals. It 11separates the brightness information (Y) from the color information (U 12and V or Cb and Cr). The color information consists of red and blue 13*color difference* signals, this way the green component can be 14reconstructed by subtracting from the brightness component. See 15:ref:`colorspaces` for conversion examples. YUV was chosen because 16early television would only transmit brightness information. To add 17color in a way compatible with existing receivers a new signal carrier 18was added to transmit the color difference signals. 19 20 21Subsampling 22=========== 23 24YUV formats commonly encode images with a lower resolution for the chroma 25components than for the luma component. This compression technique, taking 26advantage of the human eye being more sensitive to luminance than color 27differences, is called chroma subsampling. 28 29While many combinations of subsampling factors in the horizontal and vertical 30direction are possible, common factors are 1 (no subsampling), 2 and 4, with 31horizontal subsampling always larger than or equal to vertical subsampling. 32Common combinations are named as follows. 33 34- `4:4:4`: No subsampling 35- `4:2:2`: Horizontal subsampling by 2, no vertical subsampling 36- `4:2:0`: Horizontal subsampling by 2, vertical subsampling by 2 37- `4:1:1`: Horizontal subsampling by 4, no vertical subsampling 38- `4:1:0`: Horizontal subsampling by 4, vertical subsampling by 4 39 40Subsampling the chroma component effectively creates chroma values that can be 41located in different spatial locations: 42 43- .. _yuv-chroma-centered: 44 45 The subsampled chroma value may be calculated by simply averaging the chroma 46 value of two consecutive pixels. It effectively models the chroma of a pixel 47 sited between the two original pixels. This is referred to as centered or 48 interstitially sited chroma. 49 50- .. _yuv-chroma-cosited: 51 52 The other option is to subsample chroma values in a way that place them in 53 the same spatial sites as the pixels. This may be performed by skipping every 54 other chroma sample (creating aliasing artifacts), or with filters using an 55 odd number of taps. This is referred to as co-sited chroma. 56 57The following examples show different combination of chroma siting in a 4x4 58image. 59 60.. flat-table:: 4:2:2 subsampling, interstitially sited 61 :header-rows: 1 62 :stub-columns: 1 63 64 * - 65 - 0 66 - 67 - 1 68 - 69 - 2 70 - 71 - 3 72 * - 0 73 - Y 74 - C 75 - Y 76 - 77 - Y 78 - C 79 - Y 80 * - 1 81 - Y 82 - C 83 - Y 84 - 85 - Y 86 - C 87 - Y 88 * - 2 89 - Y 90 - C 91 - Y 92 - 93 - Y 94 - C 95 - Y 96 * - 3 97 - Y 98 - C 99 - Y 100 - 101 - Y 102 - C 103 - Y 104 105.. flat-table:: 4:2:2 subsampling, co-sited 106 :header-rows: 1 107 :stub-columns: 1 108 109 * - 110 - 0 111 - 112 - 1 113 - 114 - 2 115 - 116 - 3 117 * - 0 118 - Y/C 119 - 120 - Y 121 - 122 - Y/C 123 - 124 - Y 125 * - 1 126 - Y/C 127 - 128 - Y 129 - 130 - Y/C 131 - 132 - Y 133 * - 2 134 - Y/C 135 - 136 - Y 137 - 138 - Y/C 139 - 140 - Y 141 * - 3 142 - Y/C 143 - 144 - Y 145 - 146 - Y/C 147 - 148 - Y 149 150.. flat-table:: 4:2:0 subsampling, horizontally interstitially sited, vertically co-sited 151 :header-rows: 1 152 :stub-columns: 1 153 154 * - 155 - 0 156 - 157 - 1 158 - 159 - 2 160 - 161 - 3 162 * - 0 163 - Y 164 - C 165 - Y 166 - 167 - Y 168 - C 169 - Y 170 * - 1 171 - Y 172 - 173 - Y 174 - 175 - Y 176 - 177 - Y 178 * - 2 179 - Y 180 - C 181 - Y 182 - 183 - Y 184 - C 185 - Y 186 * - 3 187 - Y 188 - 189 - Y 190 - 191 - Y 192 - 193 - Y 194 195.. flat-table:: 4:1:0 subsampling, horizontally and vertically interstitially sited 196 :header-rows: 1 197 :stub-columns: 1 198 199 * - 200 - 0 201 - 202 - 1 203 - 204 - 2 205 - 206 - 3 207 * - 0 208 - Y 209 - 210 - Y 211 - 212 - Y 213 - 214 - Y 215 * - 216 - 217 - 218 - 219 - 220 - 221 - 222 - 223 * - 1 224 - Y 225 - 226 - Y 227 - 228 - Y 229 - 230 - Y 231 * - 232 - 233 - 234 - 235 - C 236 - 237 - 238 - 239 * - 2 240 - Y 241 - 242 - Y 243 - 244 - Y 245 - 246 - Y 247 * - 248 - 249 - 250 - 251 - 252 - 253 - 254 - 255 * - 3 256 - Y 257 - 258 - Y 259 - 260 - Y 261 - 262 - Y 263 264 265.. toctree:: 266 :maxdepth: 1 267 268 pixfmt-packed-yuv 269 pixfmt-yuv-planar 270 pixfmt-yuv-luma 271 pixfmt-y8i 272 pixfmt-y12i 273 pixfmt-y16i 274 pixfmt-uv8 275 pixfmt-m420 276