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/* SPDX-License-Identifier: BSD-2-Clause */
/*
* Copyright (C) 2019, Raspberry Pi (Trading) Limited
*
* contrast.cpp - contrast (gamma) control algorithm
*/
#include <stdint.h>
#include "../contrast_status.h"
#include "../histogram.hpp"
#include "contrast.hpp"
using namespace RPi;
// This is a very simple control algorithm which simply retrieves the results of
// AGC and AWB via their "status" metadata, and applies digital gain to the
// colour channels in accordance with those instructions. We take care never to
// apply less than unity gains, as that would cause fully saturated pixels to go
// off-white.
#define NAME "rpi.contrast"
Contrast::Contrast(Controller *controller)
: ContrastAlgorithm(controller), brightness_(0.0), contrast_(1.0)
{
}
char const *Contrast::Name() const
{
return NAME;
}
void Contrast::Read(boost::property_tree::ptree const ¶ms)
{
// enable adaptive enhancement by default
config_.ce_enable = params.get<int>("ce_enable", 1);
// the point near the bottom of the histogram to move
config_.lo_histogram = params.get<double>("lo_histogram", 0.01);
// where in the range to try and move it to
config_.lo_level = params.get<double>("lo_level", 0.015);
// but don't move by more than this
config_.lo_max = params.get<double>("lo_max", 500);
// equivalent values for the top of the histogram...
config_.hi_histogram = params.get<double>("hi_histogram", 0.95);
config_.hi_level = params.get<double>("hi_level", 0.95);
config_.hi_max = params.get<double>("hi_max", 2000);
config_.gamma_curve.Read(params.get_child("gamma_curve"));
}
void Contrast::SetBrightness(double brightness)
{
brightness_ = brightness;
}
void Contrast::SetContrast(double contrast)
{
contrast_ = contrast;
}
static void fill_in_status(ContrastStatus &status, double brightness,
double contrast, Pwl &gamma_curve)
{
status.brightness = brightness;
status.contrast = contrast;
for (int i = 0; i < CONTRAST_NUM_POINTS - 1; i++) {
int x = i < 16 ? i * 1024
: (i < 24 ? (i - 16) * 2048 + 16384
: (i - 24) * 4096 + 32768);
status.points[i].x = x;
status.points[i].y = std::min(65535.0, gamma_curve.Eval(x));
}
status.points[CONTRAST_NUM_POINTS - 1].x = 65535;
status.points[CONTRAST_NUM_POINTS - 1].y = 65535;
}
void Contrast::Initialise()
{
// Fill in some default values as Prepare will run before Process gets
// called.
fill_in_status(status_, brightness_, contrast_, config_.gamma_curve);
}
void Contrast::Prepare(Metadata *image_metadata)
{
std::unique_lock<std::mutex> lock(mutex_);
image_metadata->Set("contrast.status", status_);
}
Pwl compute_stretch_curve(Histogram const &histogram,
ContrastConfig const &config)
{
Pwl enhance;
enhance.Append(0, 0);
// If the start of the histogram is rather empty, try to pull it down a
// bit.
double hist_lo = histogram.Quantile(config.lo_histogram) *
(65536 / NUM_HISTOGRAM_BINS);
double level_lo = config.lo_level * 65536;
RPI_LOG("Move histogram point " << hist_lo << " to " << level_lo);
hist_lo = std::max(
level_lo,
std::min(65535.0, std::min(hist_lo, level_lo + config.lo_max)));
RPI_LOG("Final values " << hist_lo << " -> " << level_lo);
enhance.Append(hist_lo, level_lo);
// Keep the mid-point (median) in the same place, though, to limit the
// apparent amount of global brightness shift.
double mid = histogram.Quantile(0.5) * (65536 / NUM_HISTOGRAM_BINS);
enhance.Append(mid, mid);
// If the top to the histogram is empty, try to pull the pixel values
// there up.
double hist_hi = histogram.Quantile(config.hi_histogram) *
(65536 / NUM_HISTOGRAM_BINS);
double level_hi = config.hi_level * 65536;
RPI_LOG("Move histogram point " << hist_hi << " to " << level_hi);
hist_hi = std::min(
level_hi,
std::max(0.0, std::max(hist_hi, level_hi - config.hi_max)));
RPI_LOG("Final values " << hist_hi << " -> " << level_hi);
enhance.Append(hist_hi, level_hi);
enhance.Append(65535, 65535);
return enhance;
}
Pwl apply_manual_contrast(Pwl const &gamma_curve, double brightness,
double contrast)
{
Pwl new_gamma_curve;
RPI_LOG("Manual brightness " << brightness << " contrast " << contrast);
gamma_curve.Map([&](double x, double y) {
new_gamma_curve.Append(
x, std::max(0.0, std::min(65535.0,
(y - 32768) * contrast +
32768 + brightness)));
});
return new_gamma_curve;
}
void Contrast::Process(StatisticsPtr &stats, Metadata *image_metadata)
{
(void)image_metadata;
double brightness = brightness_, contrast = contrast_;
Histogram histogram(stats->hist[0].g_hist, NUM_HISTOGRAM_BINS);
// We look at the histogram and adjust the gamma curve in the following
// ways: 1. Adjust the gamma curve so as to pull the start of the
// histogram down, and possibly push the end up.
Pwl gamma_curve = config_.gamma_curve;
if (config_.ce_enable) {
if (config_.lo_max != 0 || config_.hi_max != 0)
gamma_curve = compute_stretch_curve(histogram, config_)
.Compose(gamma_curve);
// We could apply other adjustments (e.g. partial equalisation)
// based on the histogram...?
}
// 2. Finally apply any manually selected brightness/contrast
// adjustment.
if (brightness != 0 || contrast != 1.0)
gamma_curve = apply_manual_contrast(gamma_curve, brightness,
contrast);
// And fill in the status for output. Use more points towards the bottom
// of the curve.
ContrastStatus status;
fill_in_status(status, brightness, contrast, gamma_curve);
{
std::unique_lock<std::mutex> lock(mutex_);
status_ = status;
}
}
// Register algorithm with the system.
static Algorithm *Create(Controller *controller)
{
return (Algorithm *)new Contrast(controller);
}
static RegisterAlgorithm reg(NAME, &Create);
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