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]