2.12.2. V4L2_META_FMT_VSP1_HGT (‘VSPT’)

Renesas R-Car VSP1 2-D Histogram Data

2.12.2.1. 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.

VSP1 HGT Data - (776 bytes)

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]