.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
.. _v4l2-meta-fmt-vsp1-hgt:
*******************************
V4L2_META_FMT_VSP1_HGT ('VSPT')
*******************************
Renesas R-Car VSP1 2-D Histogram Data
Description
===========
This format describes histogram data generated by the Renesas R-Car VSP1
2-D Histogram (HGT) engine.
The VSP1 HGT is a histogram computation engine that operates on HSV
data. It operates on a possibly cropped and subsampled input image and
computes the sum, maximum and minimum of the S component as well as a
weighted frequency histogram based on the H and S components.
The histogram is a matrix of 6 Hue and 32 Saturation buckets, 192 in
total. Each HSV value is added to one or more buckets with a weight
between 1 and 16 depending on the Hue areas configuration. Finding the
corresponding buckets is done by inspecting the H and S value independently.
The Saturation position **n** (0 - 31) of the bucket in the matrix is
found by the expression:
n = S / 8
The Hue position **m** (0 - 5) of the bucket in the matrix depends on
how the HGT Hue areas are configured. There are 6 user configurable Hue
Areas which can be configured to cover overlapping Hue values:
.. raw:: latex
\small
::
Area 0 Area 1 Area 2 Area 3 Area 4 Area 5
________ ________ ________ ________ ________ ________
\ /| |\ /| |\ /| |\ /| |\ /| |\ /| |\ /
\ / | | \ / | | \ / | | \ / | | \ / | | \ / | | \ /
X | | X | | X | | X | | X | | X | | X
/ \ | | / \ | | / \ | | / \ | | / \ | | / \ | | / \
/ \| |/ \| |/ \| |/ \| |/ \| |/ \| |/ \
5U 0L 0U 1L 1U 2L 2U 3L 3U 4L 4U 5L 5U 0L
<0..............................Hue Value............................255>
.. raw:: latex
\normalsize
When two consecutive areas don't overlap (n+1L is equal to nU) the boundary
value is considered as part of the lower area.
Pixels with a hue value included in the centre of an area (between nL and nU
included) are attributed to that single area and given a weight of 16. Pixels
with a hue value included in the overlapping region between two areas (between
n+1L and nU excluded) are attributed to both areas and given a weight for each
of these areas proportional to their position along the diagonal lines
(rounded down).
The Hue area setup must match one of the following constrains:
::
0L <= 0U <= 1L <= 1U <= 2L <= 2U <= 3L <= 3U <= 4L <= 4U <= 5L <= 5U
::
0U <= 1L <= 1U <= 2L <= 2U <= 3L <= 3U <= 4L <= 4U <= 5L <= 5U <= 0L
**Byte Order.**
All data is stored in memory in little endian format. Each cell in the tables
contains one byte.
.. flat-table:: VSP1 HGT Data - (776 bytes)
:header-rows: 2
:stub-columns: 0
* - Offset
- :cspan:`4` Memory
* -
- [31:24]
- [23:16]
- [15:8]
- [7:0]
* - 0
- -
- S max [7:0]
- -
- S min [7:0]
* - 4
- :cspan:`4` S sum [31:0]
* - 8
- :cspan:`4` Histogram bucket (m=0, n=0) [31:0]
* - 12
- :cspan:`4` Histogram bucket (m=0, n=1) [31:0]
* -
- :cspan:`4` ...
* - 132
- :cspan:`4` Histogram bucket (m=0, n=31) [31:0]
* - 136
- :cspan:`4` Histogram bucket (m=1, n=0) [31:0]
* -
- :cspan:`4` ...
* - 264
- :cspan:`4` Histogram bucket (m=2, n=0) [31:0]
* -
- :cspan:`4` ...
* - 392
- :cspan:`4` Histogram bucket (m=3, n=0) [31:0]
* -
- :cspan:`4` ...
* - 520
- :cspan:`4` Histogram bucket (m=4, n=0) [31:0]
* -
- :cspan:`4` ...
* - 648
- :cspan:`4` Histogram bucket (m=5, n=0) [31:0]
* -
- :cspan:`4` ...
* - 772
- :cspan:`4` Histogram bucket (m=5, n=31) [31:0]
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