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