1 .. -*- coding: utf-8; mode: rst -*-
3 .. _v4l2-meta-fmt-vsp1-hgt:
5 *******************************
6 V4L2_META_FMT_VSP1_HGT ('VSPT')
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9 Renesas R-Car VSP1 2-D Histogram Data
15 This format describes histogram data generated by the Renesas R-Car VSP1
16 2-D Histogram (HGT) engine.
18 The VSP1 HGT is a histogram computation engine that operates on HSV
19 data. It operates on a possibly cropped and subsampled input image and
20 computes the sum, maximum and minimum of the S component as well as a
21 weighted frequency histogram based on the H and S components.
23 The histogram is a matrix of 6 Hue and 32 Saturation buckets, 192 in
24 total. Each HSV value is added to one or more buckets with a weight
25 between 1 and 16 depending on the Hue areas configuration. Finding the
26 corresponding buckets is done by inspecting the H and S value independently.
28 The Saturation position **n** (0 - 31) of the bucket in the matrix is
29 found by the expression:
33 The Hue position **m** (0 - 5) of the bucket in the matrix depends on
34 how the HGT Hue areas are configured. There are 6 user configurable Hue
35 Areas which can be configured to cover overlapping Hue values:
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>
49 When two consecutive areas don't overlap (n+1L is equal to nU) the boundary
50 value is considered as part of the lower area.
52 Pixels with a hue value included in the centre of an area (between nL and nU
53 included) are attributed to that single area and given a weight of 16. Pixels
54 with a hue value included in the overlapping region between two areas (between
55 n+1L and nU excluded) are attributed to both areas and given a weight for each
56 of these areas proportional to their position along the diagonal lines
59 The Hue area setup must match one of the following constrains:
63 0L <= 0U <= 1L <= 1U <= 2L <= 2U <= 3L <= 3U <= 4L <= 4U <= 5L <= 5U
67 0U <= 1L <= 1U <= 2L <= 2U <= 3L <= 3U <= 4L <= 4U <= 5L <= 5U <= 0L
70 All data is stored in memory in little endian format. Each cell in the tables
73 .. flat-table:: VSP1 HGT Data - (776 bytes)
90 - :cspan:`4` S sum [31:0]
92 - :cspan:`4` Histogram bucket (m=0, n=0) [31:0]
94 - :cspan:`4` Histogram bucket (m=0, n=1) [31:0]
98 - :cspan:`4` Histogram bucket (m=0, n=31) [31:0]
100 - :cspan:`4` Histogram bucket (m=1, n=0) [31:0]
104 - :cspan:`4` Histogram bucket (m=2, n=0) [31:0]
108 - :cspan:`4` Histogram bucket (m=3, n=0) [31:0]
112 - :cspan:`4` Histogram bucket (m=4, n=0) [31:0]
116 - :cspan:`4` Histogram bucket (m=5, n=0) [31:0]
120 - :cspan:`4` Histogram bucket (m=5, n=31) [31:0]