diff options
Diffstat (limited to 'src/ipa')
| -rw-r--r-- | src/ipa/ipu3/algorithms/agc.cpp | 25 |
1 files changed, 18 insertions, 7 deletions
diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp index c39e213f..582f0ae1 100644 --- a/src/ipa/ipu3/algorithms/agc.cpp +++ b/src/ipa/ipu3/algorithms/agc.cpp @@ -252,10 +252,19 @@ void Agc::computeExposure(IPAFrameContext &frameContext, double yGain, * \param[in] gain The gain to apply to the frame * \return The relative luminance * - * Luma is the weighted sum of gamma-compressed R′G′B′ components of a color - * video. The luma values are normalized as 0.0 to 1.0, with 1.0 being a - * theoretical perfect reflector of 100% reference white. We use the Rec. 601 - * luma here. + * This function estimates the average relative luminance of the frame that + * would be output by the sensor if an additional \a gain was applied. + * + * The estimation is based on the AWB statistics for the current frame. Red, + * green and blue averages for all cells are first multiplied by the gain, and + * then saturated to approximate the sensor behaviour at high brightness + * values. The approximation is quite rough, as it doesn't take into account + * non-linearities when approaching saturation. + * + * The relative luminance (Y) is computed from the linear RGB components using + * the Rec. 601 formula. The values are normalized to the [0.0, 1.0] range, + * where 1.0 corresponds to a theoretical perfect reflector of 100% reference + * white. * * More detailed information can be found in: * https://en.wikipedia.org/wiki/Relative_luminance @@ -267,6 +276,7 @@ double Agc::estimateLuminance(IPAFrameContext &frameContext, { double redSum = 0, greenSum = 0, blueSum = 0; + /* Sum the per-channel averages, saturated to 255. */ for (unsigned int cellY = 0; cellY < grid.height; cellY++) { for (unsigned int cellX = 0; cellX < grid.width; cellX++) { uint32_t cellPosition = cellY * stride_ + cellX; @@ -275,10 +285,11 @@ double Agc::estimateLuminance(IPAFrameContext &frameContext, reinterpret_cast<const ipu3_uapi_awb_set_item *>( &stats->awb_raw_buffer.meta_data[cellPosition] ); + const uint8_t G_avg = (cell->Gr_avg + cell->Gb_avg) / 2; - redSum += cell->R_avg * gain; - greenSum += (cell->Gr_avg + cell->Gb_avg) / 2 * gain; - blueSum += cell->B_avg * gain; + redSum += std::min(cell->R_avg * gain, 255.0); + greenSum += std::min(G_avg * gain, 255.0); + blueSum += std::min(cell->B_avg * gain, 255.0); } } |