diff options
| -rw-r--r-- | src/ipa/ipu3/algorithms/awb.cpp | 110 |
1 files changed, 69 insertions, 41 deletions
diff --git a/src/ipa/ipu3/algorithms/awb.cpp b/src/ipa/ipu3/algorithms/awb.cpp index 91364a04..8d22aceb 100644 --- a/src/ipa/ipu3/algorithms/awb.cpp +++ b/src/ipa/ipu3/algorithms/awb.cpp @@ -11,6 +11,10 @@ #include <libcamera/base/log.h> +/** + * \file awb.h + */ + namespace libcamera { namespace ipa::ipu3::algorithms { @@ -42,47 +46,6 @@ static constexpr uint32_t kMinCellsPerZoneRatio = 255 * 90 / 100; * \struct Accumulator * \brief RGB statistics for a given zone * - * - Cells are defined in Pixels - * - Zones are defined in Cells - * - * 80 cells - * /───────────── 1280 pixels ───────────\ - * 16 zones - * 16 - * ┌────┬────┬────┬────┬────┬─ ──────┬────┐ \ - * │Cell│ │ │ │ │ | │ │ │ - * 16 │ px │ │ │ │ │ | │ │ │ - * ├────┼────┼────┼────┼────┼─ ──────┼────┤ │ - * │ │ │ │ │ │ | │ │ - * │ │ │ │ │ │ | │ │ 7 - * │ ── │ ── │ ── │ ── │ ── │ ── ── ─┤ ── │ 1 2 4 - * │ │ │ │ │ │ | │ │ 2 0 5 - * - * │ │ │ │ │ │ | │ │ z p c - * ├────┼────┼────┼────┼────┼─ ──────┼────┤ o i e - * │ │ │ │ │ │ | │ │ n x l - * │ │ | │ │ e e l - * ├─── ───┼─ ──────┼────┤ s l s - * │ │ | │ │ s - * │ │ | │ │ - * ├─── Zone of Cells ───┼─ ──────┼────┤ │ - * │ (5 x 4) │ | │ │ │ - * │ │ | │ │ │ - * ├── ───┼─ ──────┼────┤ │ - * │ │ │ | │ │ │ - * │ │ │ │ │ │ | │ │ │ - * └────┴────┴────┴────┴────┴─ ──────┴────┘ / - * - * - * The algorithm works with a fixed number of zones \a kAwbStatsSizeX x - * \a kAwbStatsSizeY. For example, a frame of 1280x720 is divided into 80x45 - * cells of [16x16] pixels. In the case of \a kAwbStatsSizeX=16 and - * \a kAwbStatsSizeY=12 the zones are made of [5x4] cells. The cells are - * left-aligned and calculated by IPAIPU3::calculateBdsGrid(). - * - * Each statistics cell represents the average value of the pixels in that cell - * split by colour components. - * * The Accumulator structure stores the sum of the average of each cell in a * zone of the image, as well as the number of cells which were unsaturated and * therefore included in the average. @@ -152,6 +115,71 @@ static const struct ipu3_uapi_ccm_mat_config imguCssCcmDefault = { 0, 0, 8191, 0 }; +/** + * \class Awb + * \brief A Grey world white balance correction algorithm + * + * The Grey World algorithm assumes that the scene, in average, is neutral grey. + * Reference: Lam, Edmund & Fung, George. (2008). Automatic White Balancing in + * Digital Photography. 10.1201/9781420054538.ch10. + * + * The IPU3 generates statistics from the Bayer Down Scaler output into a grid + * defined in the ipu3_uapi_awb_config_s structure. + * + * - Cells are defined in Pixels + * - Zones are defined in Cells + * + * 80 cells + * /───────────── 1280 pixels ───────────\ + * 16 zones + * 16 + * ┌────┬────┬────┬────┬────┬─ ──────┬────┐ \ + * │Cell│ │ │ │ │ | │ │ │ + * 16 │ px │ │ │ │ │ | │ │ │ + * ├────┼────┼────┼────┼────┼─ ──────┼────┤ │ + * │ │ │ │ │ │ | │ │ + * │ │ │ │ │ │ | │ │ 7 + * │ ── │ ── │ ── │ ── │ ── │ ── ── ─┤ ── │ 1 2 4 + * │ │ │ │ │ │ | │ │ 2 0 5 + * + * │ │ │ │ │ │ | │ │ z p c + * ├────┼────┼────┼────┼────┼─ ──────┼────┤ o i e + * │ │ │ │ │ │ | │ │ n x l + * │ │ | │ │ e e l + * ├─── ───┼─ ──────┼────┤ s l s + * │ │ | │ │ s + * │ │ | │ │ + * ├─── Zone of Cells ───┼─ ──────┼────┤ │ + * │ (5 x 4) │ | │ │ │ + * │ │ | │ │ │ + * ├── ───┼─ ──────┼────┤ │ + * │ │ │ | │ │ │ + * │ │ │ │ │ │ | │ │ │ + * └────┴────┴────┴────┴────┴─ ──────┴────┘ / + * + * + * In each cell, the ImgU computes for each colour component the average of all + * unsaturated pixels (below a programmable threshold). It also provides the + * ratio of saturated pixels in the cell. + * + * The AWB algorithm operates on a coarser grid, made by grouping cells from the + * hardware grid into zones. The number of zones is fixed to \a kAwbStatsSizeX x + * \a kAwbStatsSizeY. For example, a frame of 1280x720 is divided into 80x45 + * cells of [16x16] pixels and 16x12 zones of [5x4] cells each + * (\a kAwbStatsSizeX=16 and \a kAwbStatsSizeY=12). If the number of cells isn't + * an exact multiple of the number of zones, the right-most and bottom-most + * cells are ignored. The grid configuration is computed by + * IPAIPU3::calculateBdsGrid(). + * + * Before calculating the gains, the algorithm aggregates the cell averages for + * each zone in generateAwbStats(). Cells that have a too high ratio of + * saturated pixels are ignored, and only zones that contain enough + * non-saturated cells are then used by the algorithm. + * + * The Grey World algorithm will then estimate the red and blue gains to apply, and + * store the results in the metadata. The green gain is always set to 1. + */ + Awb::Awb() : Algorithm() { |