metafmt-vsp1-hgt.rst

  1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
  2.. c:namespace:: V4L
  3
  4.. _v4l2-meta-fmt-vsp1-hgt:
  5
  6*******************************
  7V4L2_META_FMT_VSP1_HGT ('VSPT')
  8*******************************
  9
 10Renesas R-Car VSP1 2-D Histogram Data
 11
 12
 13Description
 14===========
 15
 16This format describes histogram data generated by the Renesas R-Car VSP1
 172-D Histogram (HGT) engine.
 18
 19The VSP1 HGT is a histogram computation engine that operates on HSV
 20data. It operates on a possibly cropped and subsampled input image and
 21computes the sum, maximum and minimum of the S component as well as a
 22weighted frequency histogram based on the H and S components.
 23
 24The histogram is a matrix of 6 Hue and 32 Saturation buckets, 192 in
 25total. Each HSV value is added to one or more buckets with a weight
 26between 1 and 16 depending on the Hue areas configuration. Finding the
 27corresponding buckets is done by inspecting the H and S value independently.
 28
 29The Saturation position **n** (0 - 31) of the bucket in the matrix is
 30found by the expression:
 31
 32    n = S / 8
 33
 34The Hue position **m** (0 - 5) of the bucket in the matrix depends on
 35how the HGT Hue areas are configured. There are 6 user configurable Hue
 36Areas which can be configured to cover overlapping Hue values:
 37
 38.. raw:: latex
 39
 40    \small
 41
 42::
 43
 44         Area 0       Area 1       Area 2       Area 3       Area 4       Area 5
 45        ________     ________     ________     ________     ________     ________
 46   \   /|      |\   /|      |\   /|      |\   /|      |\   /|      |\   /|      |\   /
 47    \ / |      | \ / |      | \ / |      | \ / |      | \ / |      | \ / |      | \ /
 48     X  |      |  X  |      |  X  |      |  X  |      |  X  |      |  X  |      |  X
 49    / \ |      | / \ |      | / \ |      | / \ |      | / \ |      | / \ |      | / \
 50   /   \|      |/   \|      |/   \|      |/   \|      |/   \|      |/   \|      |/   \
 51  5U   0L      0U   1L      1U   2L      2U   3L      3U   4L      4U   5L      5U   0L
 52        <0..............................Hue Value............................255>
 53
 54
 55.. raw:: latex
 56
 57    \normalsize
 58
 59When two consecutive areas don't overlap (n+1L is equal to nU) the boundary
 60value is considered as part of the lower area.
 61
 62Pixels with a hue value included in the centre of an area (between nL and nU
 63included) are attributed to that single area and given a weight of 16. Pixels
 64with a hue value included in the overlapping region between two areas (between
 65n+1L and nU excluded) are attributed to both areas and given a weight for each
 66of these areas proportional to their position along the diagonal lines
 67(rounded down).
 68
 69The Hue area setup must match one of the following constrains:
 70
 71::
 72
 73    0L <= 0U <= 1L <= 1U <= 2L <= 2U <= 3L <= 3U <= 4L <= 4U <= 5L <= 5U
 74
 75::
 76
 77    0U <= 1L <= 1U <= 2L <= 2U <= 3L <= 3U <= 4L <= 4U <= 5L <= 5U <= 0L
 78
 79**Byte Order.**
 80All data is stored in memory in little endian format. Each cell in the tables
 81contains one byte.
 82
 83.. flat-table:: VSP1 HGT Data - (776 bytes)
 84    :header-rows:  2
 85    :stub-columns: 0
 86
 87    * - Offset
 88      - :cspan:`4` Memory
 89    * -
 90      - [31:24]
 91      - [23:16]
 92      - [15:8]
 93      - [7:0]
 94    * - 0
 95      - -
 96      - S max [7:0]
 97      - -
 98      - S min [7:0]
 99    * - 4
100      - :cspan:`4` S sum [31:0]
101    * - 8
102      - :cspan:`4` Histogram bucket (m=0, n=0) [31:0]
103    * - 12
104      - :cspan:`4` Histogram bucket (m=0, n=1) [31:0]
105    * -
106      - :cspan:`4` ...
107    * - 132
108      - :cspan:`4` Histogram bucket (m=0, n=31) [31:0]
109    * - 136
110      - :cspan:`4` Histogram bucket (m=1, n=0) [31:0]
111    * -
112      - :cspan:`4` ...
113    * - 264
114      - :cspan:`4` Histogram bucket (m=2, n=0) [31:0]
115    * -
116      - :cspan:`4` ...
117    * - 392
118      - :cspan:`4` Histogram bucket (m=3, n=0) [31:0]
119    * -
120      - :cspan:`4` ...
121    * - 520
122      - :cspan:`4` Histogram bucket (m=4, n=0) [31:0]
123    * -
124      - :cspan:`4` ...
125    * - 648
126      - :cspan:`4` Histogram bucket (m=5, n=0) [31:0]
127    * -
128      - :cspan:`4` ...
129    * - 772
130      - :cspan:`4` Histogram bucket (m=5, n=31) [31:0]