.. 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]