1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2
3.. _v4l2-meta-fmt-vsp1-hgt:
4
5*******************************
6V4L2_META_FMT_VSP1_HGT ('VSPT')
7*******************************
8
9Renesas R-Car VSP1 2-D Histogram Data
10
11
12Description
13===========
14
15This format describes histogram data generated by the Renesas R-Car VSP1
162-D Histogram (HGT) engine.
17
18The VSP1 HGT is a histogram computation engine that operates on HSV
19data. It operates on a possibly cropped and subsampled input image and
20computes the sum, maximum and minimum of the S component as well as a
21weighted frequency histogram based on the H and S components.
22
23The histogram is a matrix of 6 Hue and 32 Saturation buckets, 192 in
24total. Each HSV value is added to one or more buckets with a weight
25between 1 and 16 depending on the Hue areas configuration. Finding the
26corresponding buckets is done by inspecting the H and S value independently.
27
28The Saturation position **n** (0 - 31) of the bucket in the matrix is
29found by the expression:
30
31    n = S / 8
32
33The Hue position **m** (0 - 5) of the bucket in the matrix depends on
34how the HGT Hue areas are configured. There are 6 user configurable Hue
35Areas which can be configured to cover overlapping Hue values:
36
37.. raw:: latex
38
39    \small
40
41::
42
43         Area 0       Area 1       Area 2       Area 3       Area 4       Area 5
44        ________     ________     ________     ________     ________     ________
45   \   /|      |\   /|      |\   /|      |\   /|      |\   /|      |\   /|      |\   /
46    \ / |      | \ / |      | \ / |      | \ / |      | \ / |      | \ / |      | \ /
47     X  |      |  X  |      |  X  |      |  X  |      |  X  |      |  X  |      |  X
48    / \ |      | / \ |      | / \ |      | / \ |      | / \ |      | / \ |      | / \
49   /   \|      |/   \|      |/   \|      |/   \|      |/   \|      |/   \|      |/   \
50  5U   0L      0U   1L      1U   2L      2U   3L      3U   4L      4U   5L      5U   0L
51        <0..............................Hue Value............................255>
52
53
54.. raw:: latex
55
56    \normalsize
57
58When two consecutive areas don't overlap (n+1L is equal to nU) the boundary
59value is considered as part of the lower area.
60
61Pixels with a hue value included in the centre of an area (between nL and nU
62included) are attributed to that single area and given a weight of 16. Pixels
63with a hue value included in the overlapping region between two areas (between
64n+1L and nU excluded) are attributed to both areas and given a weight for each
65of these areas proportional to their position along the diagonal lines
66(rounded down).
67
68The Hue area setup must match one of the following constrains:
69
70::
71
72    0L <= 0U <= 1L <= 1U <= 2L <= 2U <= 3L <= 3U <= 4L <= 4U <= 5L <= 5U
73
74::
75
76    0U <= 1L <= 1U <= 2L <= 2U <= 3L <= 3U <= 4L <= 4U <= 5L <= 5U <= 0L
77
78**Byte Order.**
79All data is stored in memory in little endian format. Each cell in the tables
80contains one byte.
81
82.. flat-table:: VSP1 HGT Data - (776 bytes)
83    :header-rows:  2
84    :stub-columns: 0
85
86    * - Offset
87      - :cspan:`4` Memory
88    * -
89      - [31:24]
90      - [23:16]
91      - [15:8]
92      - [7:0]
93    * - 0
94      - -
95      - S max [7:0]
96      - -
97      - S min [7:0]
98    * - 4
99      - :cspan:`4` S sum [31:0]
100    * - 8
101      - :cspan:`4` Histogram bucket (m=0, n=0) [31:0]
102    * - 12
103      - :cspan:`4` Histogram bucket (m=0, n=1) [31:0]
104    * -
105      - :cspan:`4` ...
106    * - 132
107      - :cspan:`4` Histogram bucket (m=0, n=31) [31:0]
108    * - 136
109      - :cspan:`4` Histogram bucket (m=1, n=0) [31:0]
110    * -
111      - :cspan:`4` ...
112    * - 264
113      - :cspan:`4` Histogram bucket (m=2, n=0) [31:0]
114    * -
115      - :cspan:`4` ...
116    * - 392
117      - :cspan:`4` Histogram bucket (m=3, n=0) [31:0]
118    * -
119      - :cspan:`4` ...
120    * - 520
121      - :cspan:`4` Histogram bucket (m=4, n=0) [31:0]
122    * -
123      - :cspan:`4` ...
124    * - 648
125      - :cspan:`4` Histogram bucket (m=5, n=0) [31:0]
126    * -
127      - :cspan:`4` ...
128    * - 772
129      - :cspan:`4` Histogram bucket (m=5, n=31) [31:0]
130