Implementation of Contrast-Limited Adaptive Histogram Equalization (CLAHE). More...

Inheritance diagram for Ocean::CV::ContrastLimitedAdaptiveHistogram:

Public Types
typedef std::array< unsigned int, histogramSize >	TileHistogram
	Tile histogram. More...

typedef LookupCenter2< uint8_t >	TileLookupCenter2
	Image partitioning and tile boundary lookup. More...

Static Public Member Functions
static void	equalization8BitPerChannel (const uint8_t const source, const unsigned int width, const unsigned height, uint8_t const target, const Scalar clipLimit=Scalar(40), const unsigned int horizontalTiles=8u, const unsigned int verticalTiles=8u, const unsigned int sourcePaddingElements=0u, const unsigned int targetPaddingElements=0u, Worker *worker=nullptr)
	Histogram equalization a la CLAHE. More...

Static Public Attributes
static constexpr unsigned int	histogramSize = 256u
	Number of bins in the tile histograms. More...

Static Protected Member Functions
static void	computeLookupTable (const uint8_t source, const unsigned int width, const unsigned int height, uint8_t const lookupTable, const Scalar clipLimit, const unsigned int sourcePaddingElements=0u)
	Computation of a lookup table required to normalize an image histogram (used per tile) More...

static void	computeTileLookupTables (const uint8_t const source, const TileLookupCenter2 &lookupCenter2, std::vector< uint8_t > &tileLookupTables, const Scalar clipLimit, const unsigned int sourcePaddingElements=0u, Worker worker=nullptr)
	Computation of per-tile lookup tables required to normalize an image histogram given a partitioned image. More...

static void	computeLowBilinearInterpolationFactors7BitPrecision (const TileLookupCenter2 &lookupCenter2, const bool isHorizontal, Index32 lowBins, uint8_t lowFactors_fixed7)
	Computation of the bilinear interpolation parameters for the low bins of an image pixel If `isHorizontal == true`, this function computes the horizontal interpolation parameters, i.e., the left bins and left interpolation factors, otherwise it will compute the top bins and interpolation factors. More...

static void	bilinearInterpolation (const uint8_t const source, const TileLookupCenter2 &lookupCenter2, uint8_t const target, const std::vector< uint8_t > &tileLookupTables, const unsigned int sourcePaddingElements=0u, const unsigned int targetPaddingElements=0u, Worker *worker=nullptr)
	Histogram normalization by bilinearly interpolating pixels using the CLAHE per-tile lookup tables. More...

static void	computeTileLookupTablesSubset (const uint8_t const source, const TileLookupCenter2 lookupCenter2, uint8_t *const tileLookupTables, const Scalar clipLimit, const unsigned int sourcePaddingElements=0u, const unsigned int firstTile=0u, const unsigned int tileCount=0u)
	Helper function for the computation of per-tile lookup tables required to normalize an image histogram given a partitioned image. More...

static void	bilinearInterpolation7BitPrecisionSubset (const uint8_t const source, const TileLookupCenter2 lookupCenter2, uint8_t const target, const uint8_t const tileLookupTables, const Index32 const leftBins, const uint8_t const leftFactors_fixed7, const unsigned int sourcePaddingElements=0u, const unsigned int targetPaddingElements=0u, const unsigned int rowStart=0u, const unsigned int rowCount=0u)
	Integer-based (fixed-point arithmetic) helper function for the histogram normalization by bilinearly interpolating pixels using the CLAHE per-tile lookup tables. More...

static void	bilinearInterpolationNEON7BitPrecisionSubset (const uint8_t const source, const TileLookupCenter2 lookupCenter2, uint8_t const target, const uint8_t const tileLookupTables, const Index32 const leftBins, const uint8_t const leftFactors_fixed7, const Index32 const topBins, const uint8_t const topFactors_fixed7, const unsigned int sourcePaddingElements=0u, const unsigned int targetPaddingElements=0u, const unsigned int tileStart=0u, const unsigned int tileCount=0u)
	Helper function for the histogram normalization by bilinearly interpolating pixels using the CLAHE per-tile lookup tables. More...

Detailed Description

Implementation of Contrast-Limited Adaptive Histogram Equalization (CLAHE).

Member Typedef Documentation

◆ TileHistogram

typedef std::array<unsigned int, histogramSize> Ocean::CV::ContrastLimitedAdaptiveHistogram::TileHistogram

Tile histogram.

◆ TileLookupCenter2

typedef LookupCenter2<uint8_t> Ocean::CV::ContrastLimitedAdaptiveHistogram::TileLookupCenter2

Image partitioning and tile boundary lookup.

Member Function Documentation

◆ bilinearInterpolation()

static void Ocean::CV::ContrastLimitedAdaptiveHistogram::bilinearInterpolation	(	const uint8_t *const	source,
		const TileLookupCenter2 &	lookupCenter2,
		uint8_t *const	target,
		const std::vector< uint8_t > &	tileLookupTables,
		const unsigned int	sourcePaddingElements = `0u`,
		const unsigned int	targetPaddingElements = `0u`,
		Worker *	worker = `nullptr`
	)

staticprotected

Histogram normalization by bilinearly interpolating pixels using the CLAHE per-tile lookup tables.

Parameters

source	Pointer to the data of the source frame that will be processed, must be valid and 8-bit unsigned, 1-channel (`FrameType::FORMAT_Y8`)
lookupCenter2	Defines how the source frame is partitioned, image size and number of bins will be extracted from this object, must be valid
target	Pointer to the data of the target frame, must be valid and 8-bit unsigned, 1-channel (`FrameType::FORMAT_Y8`)
tileLookupTables	Storage location for the computed lookup tables; will be initialized internally to size N x 256, where N = the total number of bins
sourcePaddingElements	Number of padding elements in the source data, range: [0, infinity), default: 0
targetPaddingElements	Number of padding elements in the target data, range: [0, infinity), default: 0
worker	Optional worker instance for parallel execution, default: nullptr

◆ bilinearInterpolation7BitPrecisionSubset()

static void Ocean::CV::ContrastLimitedAdaptiveHistogram::bilinearInterpolation7BitPrecisionSubset	(	const uint8_t *const	source,
		const TileLookupCenter2 *	lookupCenter2,
		uint8_t *const	target,
		const uint8_t *const	tileLookupTables,
		const Index32 *const	leftBins,
		const uint8_t *const	leftFactors_fixed7,
		const unsigned int	sourcePaddingElements = `0u`,
		const unsigned int	targetPaddingElements = `0u`,
		const unsigned int	rowStart = `0u`,
		const unsigned int	rowCount = `0u`
	)

staticprotected

Integer-based (fixed-point arithmetic) helper function for the histogram normalization by bilinearly interpolating pixels using the CLAHE per-tile lookup tables.

Parameters

source	Pointer to the data of the source frame that will be processed, must be valid and 8-bit unsigned, 1-channel (`FrameType::FORMAT_Y8`)
lookupCenter2	Defines how the source frame is partitioned, image size and number of bins will be extracted from this object, must be valid
target	Pointer to the data of the target frame, must be valid and 8-bit unsigned, 1-channel (`FrameType::FORMAT_Y8`)
tileLookupTables	Storage location for the computed lookup tables; will be initialized internally to size N x 256, where N = the total number of bins
leftBins	Stores the indices of the closest bins left of a horizontal pixel location, must be initialized, expected size: image width
leftFactors_fixed7	Stores the horizontal interpolation factors for the left bins (as fixed-point number with 7-bit precision), must be initialized, expected size: image width
sourcePaddingElements	Number of padding elements in the source data, range: [0, infinity), default: 0
targetPaddingElements	Number of padding elements in the target data, range: [0, infinity), default: 0
rowStart	First image row to process, range: [0, height)
rowCount	Number of rows to process, range: [0, height - rowStart)

◆ bilinearInterpolationNEON7BitPrecisionSubset()

static void Ocean::CV::ContrastLimitedAdaptiveHistogram::bilinearInterpolationNEON7BitPrecisionSubset	(	const uint8_t *const	source,
		const TileLookupCenter2 *	lookupCenter2,
		uint8_t *const	target,
		const uint8_t *const	tileLookupTables,
		const Index32 *const	leftBins,
		const uint8_t *const	leftFactors_fixed7,
		const Index32 *const	topBins,
		const uint8_t *const	topFactors_fixed7,
		const unsigned int	sourcePaddingElements = `0u`,
		const unsigned int	targetPaddingElements = `0u`,
		const unsigned int	tileStart = `0u`,
		const unsigned int	tileCount = `0u`
	)

staticprotected

Helper function for the histogram normalization by bilinearly interpolating pixels using the CLAHE per-tile lookup tables.

Parameters

source	Pointer to the data of the source frame that will be processed, must be valid and 8-bit unsigned, 1-channel (`FrameType::FORMAT_Y8`)
lookupCenter2	Defines how the source frame is partitioned, image size and number of bins will be extracted from this object, must be valid
target	Pointer to the data of the target frame, must be valid and 8-bit unsigned, 1-channel (`FrameType::FORMAT_Y8`)
tileLookupTables	Storage location for the computed lookup tables; will be initialized internally to size N x 256, where N = the total number of bins
leftBins	Stores the indices of the closest bins left of a horizontal pixel location, must be initialized, expected size: image width
leftFactors_fixed7	Stores the horizontal interpolation factors for the left bins (as fixed-point number with 7-bit precision), must be initialized, expected size: image width
topBins	Stores the indices of the closest vertical bins above a pixel location, must be initialized, expected size: image height
topFactors_fixed7	Stores the vertical interpolation factors for the top bins (as fixed-point number with 7-bit precision), must be initialized, expected size: image height
sourcePaddingElements	Number of padding elements in the source data, range: [0, infinity), default: 0
targetPaddingElements	Number of padding elements in the target data, range: [0, infinity), default: 0
tileStart	First tile to process, range: [0, N), where N = number of tiles
tileCount	Number of tiles to process, range: [0, N - tileStart)

◆ computeLookupTable()

void Ocean::CV::ContrastLimitedAdaptiveHistogram::computeLookupTable	(	const uint8_t *	source,
		const unsigned int	width,
		const unsigned int	height,
		uint8_t *const	lookupTable,
		const Scalar	clipLimit,
		const unsigned int	sourcePaddingElements = `0u`
	)

inlinestaticprotected

Computation of a lookup table required to normalize an image histogram (used per tile)

Parameters

source	Pointer to the data of the source frame that will be processed, must be valid and 8-bit unsigned, 1-channel (`FrameType::FORMAT_Y8`)
width	The width of the source and target frames, range: [1, infinity)
height	The height of the source and target frames, range: [1, infinity)
lookupTable	Storage location for the computed lookup table, must be initialized, expected size: 256
clipLimit	Scaling factor to determine the tile clip limit, `tileClipLimit = clipLimit * N`, where `N = (tileSize / histogramSize)` is the number of pixels per bin if all pixels are distributed evenly over the histogram (average), range: [0, infinity)
sourcePaddingElements	Number of padding elements in the source data, range: [0, infinity), default: 0

◆ computeLowBilinearInterpolationFactors7BitPrecision()

static void Ocean::CV::ContrastLimitedAdaptiveHistogram::computeLowBilinearInterpolationFactors7BitPrecision	(	const TileLookupCenter2 &	lookupCenter2,
		const bool	isHorizontal,
		Index32 *	lowBins,
		uint8_t *	lowFactors_fixed7
	)

staticprotected

Computation of the bilinear interpolation parameters for the low bins of an image pixel If isHorizontal == true, this function computes the horizontal interpolation parameters, i.e., the left bins and left interpolation factors, otherwise it will compute the top bins and interpolation factors.

For the horizontal parameters (isHorizontal == true), the right counterparts can be computed as:

rightBins[i] = lowBins[i] + 1u rightFactors_fixed7[i] = 128u - lowFactors_fixed7[i]

and, similarly, for the vertical parameters (isHorizontal == false).

Note: 128u is the fixed-point, 7-bit precision equivalent of 1.0f

Parameters

lookupCenter2	Defines how the source frame is partitioned, image size and number of bins will be extracted from this object, must be valid, number of bins (`binsX()`) must >= 2
isHorizontal	If true, it will compute the horizontal interpolation parameters, otherwise the vertical parameters will be computed
lowBins	Stores the indices of the closest lower (lower = left if `isHorizontal == true`, otherwise lower = top) bins of a pixel location, must be initialized before calling this function, expected size: image width if `isHorizontal == true`, otherwise image height
lowFactors_fixed7	Stores the horizontal (if `isHorizontal == true`) or vertical (if `isHorizontal == false`) interpolation factors for the lower bins (as 8-bit fixed point numbers with 7-bit precision, i.e. range: [0, 1]), must be initialized before calling this function, expected size: image width if `isHorizontal == true`, otherwise image height

◆ computeTileLookupTables()

static void Ocean::CV::ContrastLimitedAdaptiveHistogram::computeTileLookupTables	(	const uint8_t *const	source,
		const TileLookupCenter2 &	lookupCenter2,
		std::vector< uint8_t > &	tileLookupTables,
		const Scalar	clipLimit,
		const unsigned int	sourcePaddingElements = `0u`,
		Worker *	worker = `nullptr`
	)

staticprotected

Computation of per-tile lookup tables required to normalize an image histogram given a partitioned image.

Parameters

source	Pointer to the data of the source frame that will be processed, must be valid and 8-bit unsigned, 1-channel (`FrameType::FORMAT_Y8`)
lookupCenter2	Defines how the source frame is partitioned, image size and number of bins will be extracted from this object, must be valid
tileLookupTables	Storage location for the computed lookup tables; will be initialized internally to size N x 256, where N = the total number of bins
clipLimit	Scaling factor to determine the tile clip limit, `tileClipLimit = clipLimit * N`, where `N = (tileSize / histogramSize)` is the number of pixels per bin if all pixels are distributed evenly over the histogram (average), range: [0, infinity)
sourcePaddingElements	Number of padding elements in the source data, range: [0, infinity), default: 0
worker	Optional worker instance for parallel execution, default: nullptr

◆ computeTileLookupTablesSubset()

static void Ocean::CV::ContrastLimitedAdaptiveHistogram::computeTileLookupTablesSubset	(	const uint8_t *const	source,
		const TileLookupCenter2 *	lookupCenter2,
		uint8_t *const	tileLookupTables,
		const Scalar	clipLimit,
		const unsigned int	sourcePaddingElements = `0u`,
		const unsigned int	firstTile = `0u`,
		const unsigned int	tileCount = `0u`
	)

staticprotected

Helper function for the computation of per-tile lookup tables required to normalize an image histogram given a partitioned image.

Parameters

source	Pointer to the data of the source frame that will be processed, must be valid and 8-bit unsigned, 1-channel (`FrameType::FORMAT_Y8`)
lookupCenter2	Defines how the source frame is partitioned, image size and number of bins will be extracted from this object, must be valid
tileLookupTables	Storage location for the computed lookup tables; will be initialized internally to size N x 256, where N = the total number of bins
clipLimit	Scaling factor to determine the tile clip limit, `tileClipLimit = clipLimit * N`, where `N = (tileSize / histogramSize)` is the number of pixels per bin if all pixels are distributed evenly over the histogram (average), range: [0, infinity)
sourcePaddingElements	Number of padding elements in the source data, range: [0, infinity), default: 0
firstTile	Index of first tile to process, range: [0, N), where N is the total number of tiles
tileCount	Number of tiles to process, range: [1, N], such `firstTile + tileCount < N` where N is the total number of tiles

◆ equalization8BitPerChannel()

static void Ocean::CV::ContrastLimitedAdaptiveHistogram::equalization8BitPerChannel	(	const uint8_t *const	source,
		const unsigned int	width,
		const unsigned	height,
		uint8_t *const	target,
		const Scalar	clipLimit = `Scalar(40)`,
		const unsigned int	horizontalTiles = `8u`,
		const unsigned int	verticalTiles = `8u`,
		const unsigned int	sourcePaddingElements = `0u`,
		const unsigned int	targetPaddingElements = `0u`,
		Worker *	worker = `nullptr`
	)

static

Histogram equalization a la CLAHE.

Parameters

source	Pointer to the data of the source frame that will be processed, must be valid and 8-bit unsigned, 1-channel (`FrameType::FORMAT_Y8`)
width	The width of the source and target frames, range: [horizontalTiles, infinity)
height	The height of the source and target frames, range: [verticalTiles, infinity)
target	Destination location for the result, must be valid and 8-bit unsigned, 1-channel (`FrameType::FORMAT_Y8`) and have the same size as the source
clipLimit	Global scaling factor to determine the tile clip limit, `tileClipLimit = clipLimit * N`, where `N = (tileSize / histogramSize)` is the number of pixels per bin if all pixels are distributed evenly over the histogram (average), range: [0, infinity), default: 40
horizontalTiles	Number of tiles the source image will be split horizontally, range: [2, width], default: 8
verticalTiles	Number of tiles the source image will be split vertically, range: [2, height], default: 8
sourcePaddingElements	Number of padding elements in the source data, range: [0, infinity), default: 0
targetPaddingElements	Number of padding elements in the target data, range: [0, infinity), default: 0
worker	Optional worker instance for parallel execution, default: nullptr

Field Documentation

◆ histogramSize

constexpr unsigned int Ocean::CV::ContrastLimitedAdaptiveHistogram::histogramSize = 256u

staticconstexpr

Number of bins in the tile histograms.

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

Histogram.h

Public Types

Static Public Member Functions

Static Public Attributes

Static Protected Member Functions

Detailed Description

Member Typedef Documentation

◆ TileHistogram

◆ TileLookupCenter2

Member Function Documentation

◆ bilinearInterpolation()

◆ bilinearInterpolation7BitPrecisionSubset()

◆ bilinearInterpolationNEON7BitPrecisionSubset()

◆ computeLookupTable()

◆ computeLowBilinearInterpolationFactors7BitPrecision()

◆ computeTileLookupTables()

◆ computeTileLookupTablesSubset()

◆ equalization8BitPerChannel()

Field Documentation

◆ histogramSize