1.. -*- coding: utf-8; mode: rst -*-
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::
38
39         Area 0       Area 1       Area 2       Area 3       Area 4       Area 5
40        ________     ________     ________     ________     ________     ________
41   \   /|      |\   /|      |\   /|      |\   /|      |\   /|      |\   /|      |\   /
42    \ / |      | \ / |      | \ / |      | \ / |      | \ / |      | \ / |      | \ /
43     X  |      |  X  |      |  X  |      |  X  |      |  X  |      |  X  |      |  X
44    / \ |      | / \ |      | / \ |      | / \ |      | / \ |      | / \ |      | / \
45   /   \|      |/   \|      |/   \|      |/   \|      |/   \|      |/   \|      |/   \
46  5U   0L      0U   1L      1U   2L      2U   3L      3U   4L      4U   5L      5U   0L
47        <0..............................Hue Value............................255>
48
49When two consecutive areas don't overlap (n+1L is equal to nU) the boundary
50value is considered as part of the lower area.
51
52Pixels with a hue value included in the centre of an area (between nL and nU
53included) are attributed to that single area and given a weight of 16. Pixels
54with a hue value included in the overlapping region between two areas (between
55n+1L and nU excluded) are attributed to both areas and given a weight for each
56of these areas proportional to their position along the diagonal lines
57(rounded down).
58
59The Hue area setup must match one of the following constrains:
60
61::
62
63    0L <= 0U <= 1L <= 1U <= 2L <= 2U <= 3L <= 3U <= 4L <= 4U <= 5L <= 5U
64
65::
66
67    0U <= 1L <= 1U <= 2L <= 2U <= 3L <= 3U <= 4L <= 4U <= 5L <= 5U <= 0L
68
69**Byte Order.**
70All data is stored in memory in little endian format. Each cell in the tables
71contains one byte.
72
73.. flat-table:: VSP1 HGT Data - (776 bytes)
74    :header-rows:  2
75    :stub-columns: 0
76
77    * - Offset
78      - :cspan:`4` Memory
79    * -
80      - [31:24]
81      - [23:16]
82      - [15:8]
83      - [7:0]
84    * - 0
85      - -
86      - S max [7:0]
87      - -
88      - S min [7:0]
89    * - 4
90      - :cspan:`4` S sum [31:0]
91    * - 8
92      - :cspan:`4` Histogram bucket (m=0, n=0) [31:0]
93    * - 12
94      - :cspan:`4` Histogram bucket (m=0, n=1) [31:0]
95    * -
96      - :cspan:`4` ...
97    * - 132
98      - :cspan:`4` Histogram bucket (m=0, n=31) [31:0]
99    * - 136
100      - :cspan:`4` Histogram bucket (m=1, n=0) [31:0]
101    * -
102      - :cspan:`4` ...
103    * - 264
104      - :cspan:`4` Histogram bucket (m=2, n=0) [31:0]
105    * -
106      - :cspan:`4` ...
107    * - 392
108      - :cspan:`4` Histogram bucket (m=3, n=0) [31:0]
109    * -
110      - :cspan:`4` ...
111    * - 520
112      - :cspan:`4` Histogram bucket (m=4, n=0) [31:0]
113    * -
114      - :cspan:`4` ...
115    * - 648
116      - :cspan:`4` Histogram bucket (m=5, n=0) [31:0]
117    * -
118      - :cspan:`4` ...
119    * - 772
120      - :cspan:`4` Histogram bucket (m=5, n=31) [31:0]
121