| .. 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] |
