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