Binary morphology on run-length encoded image

Detailed Description

These functions support morphological operations on binary images. In order to be fast and space efficient binary images are encoded with a run-length representation. This representation groups continuous horizontal sequences of "on" pixels together in a "run". A run is charactarized by the column position of the first pixel in the run, the column position of the last pixel in the run and the row position. This representation is very compact for binary images which contain large continuous areas of "on" and "off" pixels. A checkerboard pattern would be a good example. The representation is not so suitable for binary images created from random noise images or other images where little correlation between neighboring pixels exists.

The morphological operations supported here are very similar to the operations supported in the imgproc module. In general they are fast. However on several occasions they are slower than the functions from imgproc. The structuring elements of cv::MORPH_RECT and cv::MORPH_CROSS have very good support from the imgproc module. Also small structuring elements are very fast in imgproc (presumably due to opencl support). Therefore the functions from this module are recommended for larger structuring elements (cv::MORPH_ELLIPSE or self defined structuring elements). A sample application (run_length_morphology_demo) is supplied which allows to compare the speed of some morphological operations for the functions using run-length encoding and the imgproc functions for a given image.

Run length encoded images are stored in standard opencv images. Images have a single column of cv::Point3i elements. The number of rows is the number of run + 1. The first row contains the size of the original (not encoded) image. For the runs the following mapping is used (x: column begin, y: column end (last column), z: row).

The size of the original image is required for compatibility with the imgproc functions when the boundary handling requires that pixel outside the image boundary are "on".

Functions
void	cv::ximgproc::rl::createRLEImage (const std::vector< cv::Point3i > &runs, OutputArray res, Size size=Size(0, 0))
	Creates a run-length encoded image from a vector of runs (column begin, column end, row)
void	cv::ximgproc::rl::dilate (InputArray rlSrc, OutputArray rlDest, InputArray rlKernel, Point anchor=Point(0, 0))
	Dilates an run-length encoded binary image by using a specific structuring element.
void	cv::ximgproc::rl::erode (InputArray rlSrc, OutputArray rlDest, InputArray rlKernel, bool bBoundaryOn=true, Point anchor=Point(0, 0))
	Erodes an run-length encoded binary image by using a specific structuring element.
cv::Mat	cv::ximgproc::rl::getStructuringElement (int shape, Size ksize)
	Returns a run length encoded structuring element of the specified size and shape.
bool	cv::ximgproc::rl::isRLMorphologyPossible (InputArray rlStructuringElement)
	Check whether a custom made structuring element can be used with run length morphological operations. (It must consist of a continuous array of single runs per row)
void	cv::ximgproc::rl::morphologyEx (InputArray rlSrc, OutputArray rlDest, int op, InputArray rlKernel, bool bBoundaryOnForErosion=true, Point anchor=Point(0, 0))
	Applies a morphological operation to a run-length encoded binary image.
void	cv::ximgproc::rl::paint (InputOutputArray image, InputArray rlSrc, const cv::Scalar &value)
	Paint run length encoded binary image into an image.
void	cv::ximgproc::rl::threshold (InputArray src, OutputArray rlDest, double thresh, int type)
	Applies a fixed-level threshold to each array element.

Function Documentation

createRLEImage()

void cv::ximgproc::rl::createRLEImage	(	const std::vector< cv::Point3i > &	runs,
		OutputArray	res,
		Size	size = Size(0, 0)
	)

#include <opencv2/ximgproc/run_length_morphology.hpp>

Creates a run-length encoded image from a vector of runs (column begin, column end, row)

Parameters

runs	vector of runs
res	result
size	image size (to be used if an "on" boundary should be used in erosion, using the default means that the size is computed from the extension of the input)

dilate()

void cv::ximgproc::rl::dilate	(	InputArray	rlSrc,
		OutputArray	rlDest,
		InputArray	rlKernel,
		Point	anchor = Point(0, 0)
	)

#include <opencv2/ximgproc/run_length_morphology.hpp>

Dilates an run-length encoded binary image by using a specific structuring element.

Parameters

rlSrc	input image
rlDest	result
rlKernel	kernel
anchor	position of the anchor within the element; default value (0, 0) is usually the element center.

erode()

void cv::ximgproc::rl::erode	(	InputArray	rlSrc,
		OutputArray	rlDest,
		InputArray	rlKernel,
		bool	bBoundaryOn = true,
		Point	anchor = Point(0, 0)
	)

#include <opencv2/ximgproc/run_length_morphology.hpp>

Erodes an run-length encoded binary image by using a specific structuring element.

Parameters

rlSrc	input image
rlDest	result
rlKernel	kernel
bBoundaryOn	indicates whether pixel outside the image boundary are assumed to be on (True: works in the same way as the default of cv::erode, False: is a little faster)
anchor	position of the anchor within the element; default value (0, 0) is usually the element center.

getStructuringElement()

cv::Mat cv::ximgproc::rl::getStructuringElement	(	int	shape,
		Size	ksize
	)

#include <opencv2/ximgproc/run_length_morphology.hpp>

Returns a run length encoded structuring element of the specified size and shape.

Parameters

shape	Element shape that can be one of cv::MorphShapes
ksize	Size of the structuring element.

isRLMorphologyPossible()

bool cv::ximgproc::rl::isRLMorphologyPossible

(

InputArray

rlStructuringElement

)

#include <opencv2/ximgproc/run_length_morphology.hpp>

Check whether a custom made structuring element can be used with run length morphological operations. (It must consist of a continuous array of single runs per row)

Parameters

rlStructuringElement

mask to be tested

morphologyEx()

void cv::ximgproc::rl::morphologyEx	(	InputArray	rlSrc,
		OutputArray	rlDest,
		int	op,
		InputArray	rlKernel,
		bool	bBoundaryOnForErosion = true,
		Point	anchor = Point(0, 0)
	)

#include <opencv2/ximgproc/run_length_morphology.hpp>

Applies a morphological operation to a run-length encoded binary image.

Parameters

rlSrc	input image
rlDest	result
op	all operations supported by cv::morphologyEx (except cv::MORPH_HITMISS)
rlKernel	kernel
bBoundaryOnForErosion	indicates whether pixel outside the image boundary are assumed to be on for erosion operations (True: works in the same way as the default of cv::erode, False: is a little faster)
anchor	position of the anchor within the element; default value (0, 0) is usually the element center.

paint()

void cv::ximgproc::rl::paint	(	InputOutputArray	image,
		InputArray	rlSrc,
		const cv::Scalar &	value
	)

#include <opencv2/ximgproc/run_length_morphology.hpp>

Paint run length encoded binary image into an image.

Parameters

image	image to paint into (currently only single channel images).
rlSrc	run length encoded image
value	all foreground pixel of the binary image are set to this value

threshold()

void cv::ximgproc::rl::threshold	(	InputArray	src,
		OutputArray	rlDest,
		double	thresh,
		int	type
	)

#include <opencv2/ximgproc/run_length_morphology.hpp>

Applies a fixed-level threshold to each array element.

Parameters

src	input array (single-channel).
rlDest	resulting run length encoded image.
thresh	threshold value.
type	thresholding type (only cv::THRESH_BINARY and cv::THRESH_BINARY_INV are supported)