# 2.13.6. V4L2_META_FMT_VSP1_HGT (‘VSPT’)¶

Renesas R-Car VSP1 2-D Histogram Data

## 2.13.6.1. 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:

```
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>
```

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.

Offset |
Memory |
||||
---|---|---|---|---|---|

[31:24] |
[23:16] |
[15:8] |
[7:0] |
||

0 |
S max [7:0] |
S min [7:0] |
|||

4 |
S sum [31:0] |
||||

8 |
Histogram bucket (m=0, n=0) [31:0] |
||||

12 |
Histogram bucket (m=0, n=1) [31:0] |
||||

… |
|||||

132 |
Histogram bucket (m=0, n=31) [31:0] |
||||

136 |
Histogram bucket (m=1, n=0) [31:0] |
||||

… |
|||||

264 |
Histogram bucket (m=2, n=0) [31:0] |
||||

… |
|||||

392 |
Histogram bucket (m=3, n=0) [31:0] |
||||

… |
|||||

520 |
Histogram bucket (m=4, n=0) [31:0] |
||||

… |
|||||

648 |
Histogram bucket (m=5, n=0) [31:0] |
||||

… |
|||||

772 |
Histogram bucket (m=5, n=31) [31:0] |