2 files changed, 24 insertions, 6 deletions
diff --git a/src/ipa/libipa/histogram.cpp b/src/ipa/libipa/histogram.cpp
index e7b80900..633dbd05 100644
--- a/src/ipa/libipa/histogram.cpp
+++ b/src/ipa/libipa/histogram.cpp
@@ -39,17 +39,23 @@ namespace ipa {
 
 /**
  * \brief Create a cumulative histogram
- * \param[in] data A pre-sorted histogram to be passed
+ * \param[in] data A (non-cumulative) histogram
  */
 Histogram::Histogram(Span<const uint32_t> data)
 {
-	cumulative_.reserve(data.size());
-	cumulative_.push_back(0);
-	for (const uint32_t &value : data)
-		cumulative_.push_back(cumulative_.back() + value);
+	cumulative_.resize(data.size() + 1);
+	cumulative_[0] = 0;
+	for (const auto &[i, value] : utils::enumerate(data))
+		cumulative_[i + 1] = cumulative_[i] + value;
 }
 
 /**
+ * \brief Create a cumulative histogram
+ * \param[in] data A (non-cumulative) histogram
+ * \param[in] transform The transformation function to apply to every bin
+ */
+
+/**
  * \fn Histogram::bins()
  * \brief Retrieve the number of bins currently used by the Histogram
  * \return Number of bins
diff --git a/src/ipa/libipa/histogram.h b/src/ipa/libipa/histogram.h
index 0379ab53..032adca0 100644
--- a/src/ipa/libipa/histogram.h
+++ b/src/ipa/libipa/histogram.h
@@ -10,10 +10,11 @@
 #include <assert.h>
 #include <limits.h>
 #include <stdint.h>
-
+#include <type_traits>
 #include <vector>
 
 #include <libcamera/base/span.h>
+#include <libcamera/base/utils.h>
 
 namespace libcamera {
 
@@ -24,6 +25,17 @@ class Histogram
 public:
 	Histogram() { cumulative_.push_back(0); }
 	Histogram(Span<const uint32_t> data);
+
+	template<typename Transform,
+		 std::enable_if_t<std::is_invocable_v<Transform, uint32_t>> * = nullptr>
+	Histogram(Span<const uint32_t> data, Transform transform)
+	{
+		cumulative_.resize(data.size() + 1);
+		cumulative_[0] = 0;
+		for (const auto &[i, value] : utils::enumerate(data))
+			cumulative_[i + 1] = cumulative_[i] + transform(value);
+	}
+
 	size_t bins() const { return cumulative_.size() - 1; }
 	uint64_t total() const { return cumulative_[cumulative_.size() - 1]; }
 	uint64_t cumulativeFrequency(double bin) const;