samples/risp4ml/isp_stages/gamma.c

#include "samples/risp4ml/common/utils.h"
#include "samples/risp4ml/isp_stages/gamma.h"

#define kRgbColorChannels 3

static const uint16_t kRgbPipelineBpp = 16;
static const uint32_t kRgbPipelineMaxVal = (1 << kRgbPipelineBpp) - 1;

// Fixed HW Parameters
static const uint8_t kGammaNumberSegments = 4;
static const uint8_t kGammaLogSegmentOffsets[] = {0, 3, 2, 1};
static const uint8_t kGammaLogSegmentSpacing[] = {8, 9, 10, 11};
static const uint16_t kGammaLogNumberPoints[] = {5, 4, 4, 4};
static const uint16_t kGammaSegmentLutOffset[] = {0, 32, 48, 64};

static GammaParams gamma_params = {
    .enable = true,
    .lut = {0,     3255,  5552,  7237,  8618,  9809,  10868, 11828, 12710,
            13531, 14300, 15026, 15713, 16368, 16995, 17596, 18173, 18731,
            19269, 19790, 20295, 20786, 21264, 21728, 22182, 22624, 23056,
            23479, 23892, 24297, 24694, 25083, 25466, 26209, 26928, 27623,
            28298, 28953, 29590, 30211, 30816, 31406, 31983, 32547, 33099,
            33640, 34170, 34689, 35199, 36192, 37151, 38080, 38980, 39855,
            40705, 41534, 42341, 43129, 43899, 44652, 45389, 46111, 46818,
            47512, 48192, 49517, 50798, 52037, 53239, 54407, 55542, 56648,
            57726, 58778, 59806, 60811, 61794, 62757, 63702, 64627, 65535}};

void set_gamma_params(GammaParams* params) { gamma_params = *params; }

void gamma_process(Image* img) {
  if (!gamma_params.enable) return;

  pixel_type_t* line[kRgbColorChannels];

  for (uint16_t y = 0; y < img->height; ++y) {
    for (uint16_t c = 0; c < kRgbColorChannels; ++c) {
      line[c] = image_row(img, c, y);
    }

    for (uint16_t x = 0; x < img->width; ++x) {
      for (uint16_t c = 0; c < kRgbColorChannels; ++c) {
        pixel_type_t pixel_val =
            (pixel_type_t)Clamp(line[c][x], 0, kRgbPipelineMaxVal);

        // Determine segment
        int segment_index =
            (kGammaNumberSegments - 1) -
            ClzMsb(pixel_val, kRgbPipelineBpp, kGammaNumberSegments - 1);
        uint16_t segment_left =
            segment_index ? 1 << (kRgbPipelineBpp -
                                  kGammaLogSegmentOffsets[segment_index])
                          : 0;

        // Bin index
        int bin_index = ((pixel_val - segment_left) >>
                         kGammaLogSegmentSpacing[segment_index]) +
                        kGammaSegmentLutOffset[segment_index];

        int offset_within_bin =
            (pixel_val - segment_left) &
            ((1 << kGammaLogSegmentSpacing[segment_index]) - 1);

        uint16_t l_val = gamma_params.lut[bin_index];
        uint16_t r_val = gamma_params.lut[bin_index + 1];

        uint16_t bin_size = 1 << kGammaLogSegmentSpacing[segment_index];

        uint32_t lerp_val = (l_val * (bin_size - offset_within_bin) +
                             r_val * offset_within_bin + (bin_size >> 1)) >>
                            kGammaLogSegmentSpacing[segment_index];

        // Clamping is not requied
        // TODO(alexkaplan): The comment above is from gChips source.
        // this calc needs to be checked carefully:
        //
        line[c][x] = (pixel_type_t)lerp_val;
      }
    }
  }
}