ipa: rpi: Add HDR support

Add support for the following HDR modes in the Raspberry Pi IPA:
- Night mode
- Single exposure mode
- Multi-exposure (merged and unmerged)

The algorithm is updated to expect the HDR short channel to meter
explicitly for highlights. This means that it will not in general
under-expose the short channel more than is actually necessary.

When images don't have much saturation, it's good to detect this so
that some of the boost we want to apply to the dark areas can be
implemented as regular gain. This means we can then adjust the tone
curve less, leading to less flat looking images.

The impact on the HDR algorithm is then that this determines how we
build tonemaps dynamically. The highlights are more-or-less correct
now, so we have to build a power-type curve that gives us the
appropriately configured targets in the lower part of the histogram.

We allow the tuning file to supply the maximum spatial gain value,
rather than the whole curve (though it can supply this if it
wants). Some parameter defaults are tweaked to be generally better
across the range of our cameras.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>

2 files changed, 105 insertions, 17 deletions

diff --git a/src/ipa/rpi/controller/rpi/hdr.cpp b/src/ipa/rpi/controller/rpi/hdr.cpp
index fb580548..28c2280a 100644
--- a/src/ipa/rpi/controller/rpi/hdr.cpp
+++ b/src/ipa/rpi/controller/rpi/hdr.cpp
@@ -7,6 +7,8 @@
 
 #include "hdr.h"
 
+#include <cmath>
+
 #include <libcamera/base/log.h>
 
 #include "../agc_status.h"
@@ -39,25 +41,52 @@ void HdrConfig::read(const libcamera::YamlObject &params, const std::string &mod
 		channelMap[v.get<unsigned int>().value()] = k;
 
 	/* Lens shading related parameters. */
-	if (params.contains("spatial_gain")) {
-		spatialGain.read(params["spatial_gain"]);
-		diffusion = params["diffusion"].get<unsigned int>(3);
-		/* Clip to an arbitrary limit just to stop typos from killing the system! */
-		const unsigned int MAX_DIFFUSION = 15;
-		if (diffusion > MAX_DIFFUSION) {
-			diffusion = MAX_DIFFUSION;
-			LOG(RPiHdr, Warning) << "Diffusion value clipped to " << MAX_DIFFUSION;
-		}
+	if (params.contains("spatial_gain_curve")) {
+		spatialGainCurve.read(params["spatial_gain_curve"]);
+	} else if (params.contains("spatial_gain")) {
+		double spatialGain = params["spatial_gain"].get<double>(2.0);
+		spatialGainCurve.append(0.0, spatialGain);
+		spatialGainCurve.append(0.01, spatialGain);
+		spatialGainCurve.append(0.06, 1.0); /* maybe make this programmable? */
+		spatialGainCurve.append(1.0, 1.0);
+	}
+
+	diffusion = params["diffusion"].get<unsigned int>(3);
+	/* Clip to an arbitrary limit just to stop typos from killing the system! */
+	const unsigned int MAX_DIFFUSION = 15;
+	if (diffusion > MAX_DIFFUSION) {
+		diffusion = MAX_DIFFUSION;
+		LOG(RPiHdr, Warning) << "Diffusion value clipped to " << MAX_DIFFUSION;
 	}
 
 	/* Read any tonemap parameters. */
 	tonemapEnable = params["tonemap_enable"].get<int>(0);
-	detailConstant = params["detail_constant"].get<uint16_t>(50);
-	detailSlope = params["detail_slope"].get<double>(8.0);
+	detailConstant = params["detail_constant"].get<uint16_t>(0);
+	detailSlope = params["detail_slope"].get<double>(0.0);
 	iirStrength = params["iir_strength"].get<double>(8.0);
 	strength = params["strength"].get<double>(1.5);
 	if (tonemapEnable)
 		tonemap.read(params["tonemap"]);
+	speed = params["speed"].get<double>(1.0);
+	if (params.contains("hi_quantile_targets")) {
+		hiQuantileTargets = params["hi_quantile_targets"].getList<double>().value();
+		if (hiQuantileTargets.empty() || hiQuantileTargets.size() % 2)
+			LOG(RPiHdr, Fatal) << "hi_quantile_targets much be even and non-empty";
+	} else
+		hiQuantileTargets = { 0.95, 0.65, 0.5, 0.28, 0.3, 0.25 };
+	hiQuantileMaxGain = params["hi_quantile_max_gain"].get<double>(1.6);
+	if (params.contains("quantile_targets")) {
+		quantileTargets = params["quantile_targets"].getList<double>().value();
+		if (quantileTargets.empty() || quantileTargets.size() % 2)
+			LOG(RPiHdr, Fatal) << "quantile_targets much be even and non-empty";
+	} else
+		quantileTargets = { 0.2, 0.03, 1.0, 0.15 };
+	powerMin = params["power_min"].get<double>(0.65);
+	powerMax = params["power_max"].get<double>(1.0);
+	if (params.contains("contrast_adjustments")) {
+		contrastAdjustments = params["contrast_adjustments"].getList<double>().value();
+	} else
+		contrastAdjustments = { 0.5, 0.75 };
 
 	/* Read any stitch parameters. */
 	stitchEnable = params["stitch_enable"].get<int>(0);
@@ -159,7 +188,7 @@ void Hdr::prepare(Metadata *imageMetadata)
 	}
 
 	HdrConfig &config = it->second;
-	if (config.spatialGain.empty())
+	if (config.spatialGainCurve.empty())
 		return;
 
 	AlscStatus alscStatus{}; /* some compilers seem to require the braces */
@@ -205,10 +234,61 @@ bool Hdr::updateTonemap([[maybe_unused]] StatisticsPtr &stats, HdrConfig &config
 		return true;
 
 	/*
-	 * If we wanted to build or adjust tonemaps dynamically, this would be the place
-	 * to do it. But for now we seem to be getting by without.
+	 * Create a tonemap dynamically. We have three ingredients.
+	 *
+	 * 1. We have a list of "hi quantiles" and "targets". We use these to judge if
+	 * the image does seem to be reasonably saturated. If it isn't, we calculate
+	 * a gain that we will feed as a linear factor into the tonemap generation.
+	 * This prevents unsaturated images from beoming quite so "flat".
+	 *
+	 * 2. We have a list of quantile/target pairs for the bottom of the histogram.
+	 * We use these to calculate how much gain we must apply to the bottom of the
+	 * tonemap. We apply this gain as a power curve so as not to blow out the top
+	 * end.
+	 *
+	 * 3. Finally, when we generate the tonemap, we have some contrast adjustments
+	 * for the bottom because we know that power curves can start quite steeply and
+	 * cause a washed-out look.
 	 */
 
+	/* Compute the linear gain from the headroom for saturation at the top. */
+	double gain = 10; /* arbitrary, but hiQuantileMaxGain will clamp it later */
+	for (unsigned int i = 0; i < config.hiQuantileTargets.size(); i += 2) {
+		double quantile = config.hiQuantileTargets[i];
+		double target = config.hiQuantileTargets[i + 1];
+		double value = stats->yHist.interQuantileMean(quantile, 1.0) / 1024.0;
+		double newGain = target / (value + 0.01);
+		gain = std::min(gain, newGain);
+	}
+	gain = std::clamp(gain, 1.0, config.hiQuantileMaxGain);
+
+	/* Compute the power curve from the amount of gain needed at the bottom. */
+	double min_power = 2; /* arbitrary, but config.powerMax will clamp it later */
+	for (unsigned int i = 0; i < config.quantileTargets.size(); i += 2) {
+		double quantile = config.quantileTargets[i];
+		double target = config.quantileTargets[i + 1];
+		double value = stats->yHist.interQuantileMean(0, quantile) / 1024.0;
+		value = std::min(value * gain, 1.0);
+		double power = log(target + 1e-6) / log(value + 1e-6);
+		min_power = std::min(min_power, power);
+	}
+	double power = std::clamp(min_power, config.powerMin, config.powerMax);
+
+	/* Generate the tonemap, including the contrast adjustment factors. */
+	Pwl tonemap;
+	tonemap.append(0, 0);
+	for (unsigned int i = 0; i <= 6; i++) {
+		double x = 1 << (i + 9); /* x loops from 512 to 32768 inclusive */
+		double y = pow(std::min(x * gain, 65535.0) / 65536.0, power) * 65536;
+		if (i < config.contrastAdjustments.size())
+			y *= config.contrastAdjustments[i];
+		if (!tonemap_.empty())
+			y = y * config.speed + tonemap_.eval(x) * (1 - config.speed);
+		tonemap.append(x, y);
+	}
+	tonemap.append(65535, 65535);
+	tonemap_ = tonemap;
+
 	return true;
 }
 
@@ -255,7 +335,7 @@ static void averageGains(std::vector<double> &src, std::vector<double> &dst, con
 
 void Hdr::updateGains(StatisticsPtr &stats, HdrConfig &config)
 {
-	if (config.spatialGain.empty())
+	if (config.spatialGainCurve.empty())
 		return;
 
 	/* When alternating exposures, only compute these gains for the short frame. */
@@ -270,7 +350,7 @@ void Hdr::updateGains(StatisticsPtr &stats, HdrConfig &config)
 		double g = region.val.gSum / counted;
 		double b = region.val.bSum / counted;
 		double brightness = std::max({ r, g, b }) / 65535;
-		gains_[0][i] = config.spatialGain.eval(brightness);
+		gains_[0][i] = config.spatialGainCurve.eval(brightness);
 	}
 
 	/* Ping-pong between the two gains_ buffers. */
diff --git a/src/ipa/rpi/controller/rpi/hdr.h b/src/ipa/rpi/controller/rpi/hdr.h
index 980aa3d1..ac855b22 100644
--- a/src/ipa/rpi/controller/rpi/hdr.h
+++ b/src/ipa/rpi/controller/rpi/hdr.h
@@ -26,7 +26,7 @@ struct HdrConfig {
 	std::map<unsigned int, std::string> channelMap;
 
 	/* Lens shading related parameters. */
-	Pwl spatialGain; /* Brightness to gain curve for different image regions. */
+	Pwl spatialGainCurve; /* Brightness to gain curve for different image regions. */
 	unsigned int diffusion; /* How much to diffuse the gain spatially. */
 
 	/* Tonemap related parameters. */
@@ -36,6 +36,14 @@ struct HdrConfig {
 	double iirStrength;
 	double strength;
 	Pwl tonemap;
+	/* These relate to adaptive tonemap calculation. */
+	double speed;
+	std::vector<double> hiQuantileTargets; /* quantiles to check for unsaturated images */
+	double hiQuantileMaxGain; /* the max gain we'll apply when unsaturated */
+	std::vector<double> quantileTargets; /* target values for histogram quantiles */
+	double powerMin; /* minimum tonemap power */
+	double powerMax; /* maximum tonemap power */
+	std::vector<double> contrastAdjustments; /* any contrast adjustment factors */
 
 	/* Stitch related parameters. */
 	bool stitchEnable;