libcamera  v0.2.0+31-5e4dc46a
Supporting cameras in Linux since 2019
Public Member Functions | List of all members
libcamera::ipa::Histogram Class Reference

The base class for creating histograms. More...

Public Member Functions

 Histogram (Span< const uint32_t > data)
 Create a cumulative histogram. More...
 
size_t bins () const
 Retrieve the number of bins currently used by the Histogram. 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()

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

Create a cumulative histogram.

Parameters
[in]dataA pre-sorted histogram to be passed

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]binThe 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

◆ interQuantileMean()

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

Calculate the mean between two quantiles.

Parameters
[in]lowQuantilelow Quantile
[in]highQuantilehigh 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]qthe desired point (0 <= q <= 1)
[in]firstlow limit (default is 0)
[in]lasthigh 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: