libcamera::ipa::Histogram Class Reference

The base class for creating histograms. More...

Public Member Functions
	Histogram ()
	Construct an empty Histogram. More...
	Histogram (Span< const uint32_t > data)
	Create a cumulative histogram. More...
template<typename Transform , std::enable_if_t< std::is_invocable_v< Transform, uint32_t >> * = nullptr>
	Histogram (Span< const uint32_t > data, Transform transform)
	Create a cumulative histogram. More...
size_t	bins () const
	Retrieve the number of bins currently used by the Histogram. More...
const Span< const uint64_t >	data () const
	Retrieve the internal data. More...
uint64_t	total () const
	Retrieve the total number of values in the data set. More...
uint64_t	cumulativeFrequency (double bin) const
	Cumulative frequency up to a (fractional) point in a bin. More...
double	quantile (double q, uint32_t first=0, uint32_t last=UINT_MAX) const
	Return the (fractional) bin of the point through the histogram. More...
double	interQuantileMean (double lowQuantile, double hiQuantile) const
	Calculate the mean between two quantiles. More...

Detailed Description

The base class for creating histograms.

This class stores a cumulative frequency histogram, which is a mapping that counts the cumulative number of observations in all of the bins up to the specified bin. It can be used to find quantiles and averages between quantiles.

Constructor & Destructor Documentation

Histogram() [1/3]

libcamera::ipa::Histogram::Histogram ( )

inline

Construct an empty Histogram.

This empty constructor exists largely to allow Histograms to be embedded in other classes which may be created before the contents of the Histogram are known.

Histogram() [2/3]

libcamera::ipa::Histogram::Histogram

(

Span< const uint32_t >

data

)

Create a cumulative histogram.

Parameters

[in]

data

A (non-cumulative) histogram

Histogram() [3/3]

template<typename Transform , std::enable_if_t< std::is_invocable_v< Transform, uint32_t >> * = nullptr>

libcamera::ipa::Histogram::Histogram ( Span< const uint32_t >  data, Transform  transform  )

inline

Create a cumulative histogram.

Parameters

[in]	data	A (non-cumulative) histogram
[in]	transform	The transformation function to apply to every bin

Member Function Documentation

bins()

libcamera::ipa::Histogram::bins ( ) const

inline

Retrieve the number of bins currently used by the Histogram.

Returns

Number of bins

cumulativeFrequency()

uint64_t libcamera::ipa::Histogram::cumulativeFrequency

(

double

bin

)

const

Cumulative frequency up to a (fractional) point in a bin.

Parameters

[in]

bin

The bin up to which to cumulate

With F(p) the cumulative frequency of the histogram, the value is 0 at the bottom of the histogram, and the maximum is the number of bins. The pixels are spread evenly throughout the “bin” in which they lie, so that F(p) is a continuous (monotonically increasing) function.

Returns

The cumulative frequency from 0 up to the specified bin

data()

libcamera::ipa::Histogram::data ( ) const

inline

Retrieve the internal data.

Returns

The data

interQuantileMean()

double libcamera::ipa::Histogram::interQuantileMean	(	double	lowQuantile,
		double	highQuantile
	)		const

Calculate the mean between two quantiles.

Parameters

[in]	lowQuantile	low Quantile
[in]	highQuantile	high Quantile

Quantiles are not ideal for metering as they suffer several limitations. Instead, a concept is introduced here: inter-quantile mean. It returns the mean of all pixels between lowQuantile and highQuantile.

Returns

The mean histogram bin value between the two quantiles

quantile()

double libcamera::ipa::Histogram::quantile	(	double	q,
		uint32_t	first = 0,
		uint32_t	last = UINT_MAX
	)		const

Return the (fractional) bin of the point through the histogram.

Parameters

[in]	q	the desired point (0 <= q <= 1)
[in]	first	low limit (default is 0)
[in]	last	high limit (default is UINT_MAX)

A quantile gives us the point p = Q(q) in the range such that a proportion q of the pixels lie below p. A familiar quantile is Q(0.5) which is the median of a distribution.

Returns

The fractional bin of the point

total()

libcamera::ipa::Histogram::total ( ) const

inline

Retrieve the total number of values in the data set.

Returns

Number of values

---

The documentation for this class was generated from the following files:

• src/ipa/libipa/histogram.h
• src/ipa/libipa/histogram.cpp