libcamera: ipa: Raspberry Pi IPA

Initial implementation of the Raspberry Pi (BCM2835) libcamera IPA and
associated libraries.

All code is licensed under the BSD-2-Clause terms.
Copyright (c) 2019-2020 Raspberry Pi Trading Ltd.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

1 files changed, 64 insertions, 0 deletions

diff --git a/src/ipa/raspberrypi/controller/histogram.cpp b/src/ipa/raspberrypi/controller/histogram.cpp
new file mode 100644
index 00000000..103d3f60
--- /dev/null
+++ b/src/ipa/raspberrypi/controller/histogram.cpp
@@ -0,0 +1,64 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+/*
+ * Copyright (C) 2019, Raspberry Pi (Trading) Limited
+ *
+ * histogram.cpp - histogram calculations
+ */
+#include <math.h>
+#include <stdio.h>
+
+#include "histogram.hpp"
+
+using namespace RPi;
+
+uint64_t Histogram::CumulativeFreq(double bin) const
+{
+	if (bin <= 0)
+		return 0;
+	else if (bin >= Bins())
+		return Total();
+	int b = (int)bin;
+	return cumulative_[b] +
+	       (bin - b) * (cumulative_[b + 1] - cumulative_[b]);
+}
+
+double Histogram::Quantile(double q, int first, int last) const
+{
+	if (first == -1)
+		first = 0;
+	if (last == -1)
+		last = cumulative_.size() - 2;
+	assert(first <= last);
+	uint64_t items = q * Total();
+	while (first < last) // binary search to find the right bin
+	{
+		int middle = (first + last) / 2;
+		if (cumulative_[middle + 1] > items)
+			last = middle; // between first and middle
+		else
+			first = middle + 1; // after middle
+	}
+	assert(items >= cumulative_[first] && items <= cumulative_[last + 1]);
+	double frac = cumulative_[first + 1] == cumulative_[first] ? 0
+		      : (double)(items - cumulative_[first]) /
+				  (cumulative_[first + 1] - cumulative_[first]);
+	return first + frac;
+}
+
+double Histogram::InterQuantileMean(double q_lo, double q_hi) const
+{
+	assert(q_hi > q_lo);
+	double p_lo = Quantile(q_lo);
+	double p_hi = Quantile(q_hi, (int)p_lo);
+	double sum_bin_freq = 0, cumul_freq = 0;
+	for (double p_next = floor(p_lo) + 1.0; p_next <= ceil(p_hi);
+	     p_lo = p_next, p_next += 1.0) {
+		int bin = floor(p_lo);
+		double freq = (cumulative_[bin + 1] - cumulative_[bin]) *
+			      (std::min(p_next, p_hi) - p_lo);
+		sum_bin_freq += bin * freq;
+		cumul_freq += freq;
+	}
+	// add 0.5 to give an average for bin mid-points
+	return sum_bin_freq / cumul_freq + 0.5;
+}