cppcode/colorfilteringIPOL.cpp File Reference

Various functions for RGB cube processing (including filtering and density computation). More...

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <time.h>
#include "mdmath.h"
#include "miscIPOL.h"
#include "colorfilteringIPOL.h"

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Classes
struct	infoPixel
	Data structure containing RGB information for each image pixel. More...
struct	RGBpoint
	Data structure containg information of a color point in RGB space. More...
struct	RGBbin
	List of data structures of type RGBpoint. More...
struct	infoProjection
	Information about the projection of an RGB color point onto a line or plane. More...
Functions
int	initialize_colorfiltering_data (unsigned char R, unsigned char G, unsigned char B, int w, int h, struct RGBbin *checkOut, struct infoPixel infopixOut, struct infoPixel infopixBOut, int repeatedRGBOut, unsigned char ignore000)
	initialization of data structures for RGB cube processing
void	delete_colorfiltering_data (struct RGBbin **check, struct infoPixel infopix, struct infoPixel *infopixB)
	free memory used to store temporary data structures
void	add_neighboursRGB (float R0, float G0, float B0, struct RGBbin *check, int iR, int iG, int iB, int rneigh, struct RGBpoint firstneighIn, struct RGBpoint **lastneighIn, int &nneigh, int &nneighdiff)
	add RGB points to a list of neighbors of a given RGB point in a color image
struct RGBpoint *	find_neighboursRGB (float R0, float G0, float B0, struct RGBbin ***check, int rneigh, int nneighmax, int &nneigh, int &nneighdiff)
	create a list of neighbors of a given RGB point (RGB points at L1-distance smaller than a threshold) in a color image
void	project_point (float R0, float G0, float B0, float &newR, float &newG, float &newB, float Rcm, float Gcm, float Bcm, float vx, float vy, float vz, unsigned char option)
	project RGB point onto a line or a plane
unsigned char	get_projectionRGB (float R0, float G0, float B0, struct RGBpoint firstneigh, struct infoProjection infoproj, unsigned char option)
	get parameters of a local line or a plane in the neighborhood of a given RGB point (use PCA) and project the point onto the line (plane)
unsigned char	find_projectionRGB (float R0, float G0, float B0, struct RGBbin **check, struct infoProjection infoproj, int rneigh, int nneighmin, unsigned char option)
	find the projection of a given RGB point, from a color image, onto a locally defined line or plane
void	process_RGBpoint (float R0, float G0, float B0, unsigned char validprojection, struct RGBbin **check, struct infoPixel infopix, struct infoPixel infopixB, struct infoProjection infoproj, int rsim)
	update RGB values from the projection of initial RGB points onto local lines or planes
void	reset_color_info (struct RGBbin ***check)
	reset data structures for a new iteration of the filtering algorithm
void	compute_errors_it (struct infoPixel infopix, struct infoPixel infopixPrev, int w, int h, float &dprev, int *repeatedRGB)
	compute average difference between RGB values in current and previous iterations of the algorithm
void	update_color_info (struct RGBbin **check, struct infoPixel infopix, int w, int h)
	update color information for a new iteration of the filtering algorithm
void	get_output_image (unsigned char outR, unsigned char outG, unsigned char outB, int w, int h, struct infoPixel infopix)
	compute output image from updated RGB values
int	colorfiltering (unsigned char R, unsigned char G, unsigned char B, unsigned char outR, unsigned char outG, unsigned char outB, int w, int h, struct paramColorFilter *param)
	Main function implementing the color filtering algorithm (LLP algorithm).
struct paramColorFilter *	new_colorfiltering_parameters (int rneigh, int rsim, int nneighmin, float eitmax, unsigned char option, unsigned char ignore000)
	Organize input parameters in a data structure.
void	delete_colorfiltering_parameters (struct paramColorFilter *param)
	Delete input parameters data structure.
float ***	RGBdensities (unsigned char R, unsigned char G, unsigned char *B, int w, int h, int rdst, float hdst, float &maxdst)
	Compute the density of the colors of an image.
void	delete_RGBdensities (float ***dsts)
	Delete data structure containing density values.
void	removeisolatedRGB (unsigned char R, unsigned char G, unsigned char B, unsigned char outR, unsigned char outG, unsigned char outB, int w, int h, int r, int nmin, int &nRGB, int &nisolatedRGB, int &nisolatedpixels)
	Filter out "isolated" colors in RGB space, that is, colors with a small number of neighbors.

Detailed Description

Various functions for RGB cube processing (including filtering and density computation).

Version:: 1.0

Author:: Jose Luis Lisani; <joseluis.lisani@uib.es>

Definition in file colorfilteringIPOL.cpp.

Function Documentation

void add_neighboursRGB	(	float	R0,
		float	G0,
		float	B0,
		struct RGBbin ***	check,
		int	iR,
		int	iG,
		int	iB,
		int	rneigh,
		struct RGBpoint **	firstneighIn,
		struct RGBpoint **	lastneighIn,
		int &	nneigh,
		int &	nneighdiff
	)

add RGB points to a list of neighbors of a given RGB point in a color image

Adds to the list all the colors of the image whose RGB coordinates are in the range [iR, iR+1), [iG, iG+1), [iB, iB+1)

Parameters:

`[in]`	R0,G0,B0	initial RGB point
`[in]`	check	check[iR][iG][iB] is a pointer to a RGBbin data structure that contains the list of pixels whose color is in the range [iR, iR+1), [iG, iG+1), [iB, iB+1)
`[in]`	rneigh	threshold distance that defines the neighborhood around the initial RGB point
	in/out]	firstneighIn, lastneighIn pointers to the beginning and end of the list
`[out]`	nneigh	number of color points in the list (each point appears as many times as pixels in the image have this color)
`[out]`	nneighdiff	number of diferent colors in the list (without taking into account the number of times it is repeated in the image)

Definition at line 304 of file colorfilteringIPOL.cpp.

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int colorfiltering	(	unsigned char *	R,
		unsigned char *	G,
		unsigned char *	B,
		unsigned char *	outR,
		unsigned char *	outG,
		unsigned char *	outB,
		int	w,
		int	h,
		struct paramColorFilter *	param
	)

Main function implementing the color filtering algorithm (LLP algorithm).

Algorithm description (LLP algorithm)

Image colors are considered as points in a 3D space, namely the color cube. The algorithm replaces each RGB color in the cube by its projection onto a line (or plane) locally defined. This line (or plane) is the one that better fits the spatial distribution of the colors in a neighborhood of the considered RGB point, and it is computed by Principal Components Analysis (PCA). Only points with a large enough number of neighboring colors are projected. The process is iterated until the average error between corresponding colors in consecutive iterations is below a threshold.

Parameters:

`[in]`	R,G,B	pointers to red, green and blue channels of the input image
`[out]`	outR,outG,outB	pointers to red, green and blue channels of the output image
`[in]`	w,h	width and height of the input (and output) images
`[in]`	param	data structure with the parameters of the algorithm:
	param.rneigh	radius of local neighborhood for computation of lines or planes
	param.nneighmin	minimum number of neighbors (number of different colors) needed to compute lines or planes
	param.rsim	speed up factor, the same line or plane computed for a given RGB point is used for its neighbors at L1-distance $\leq$ rsim
	param.eitmax	stop criterion of the algorithm. The algorithm is iterated until the average difference of corresponding colors in two consecutive iterations is below eitmax
	param.option	1 project to line, 2 project to plane
	param.ignore000	if TRUE ignore (0,0,0) color points (eventually belonging to pixels discarded in a pre-processing step)

Returns:: number of iterarations of the algorithm

Definition at line 1017 of file colorfilteringIPOL.cpp.

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void compute_errors_it	(	struct infoPixel *	infopix,
		struct infoPixel *	infopixPrev,
		int	w,
		int	h,
		float &	dprev,
		int *	repeatedRGB
	)

compute average difference between RGB values in current and previous iterations of the algorithm

Parameters:

`[in]`	infopix,infoPrev	information about the colors of the pixel in the current and previous iterations of the algorithm
`[in]`	w,h	dimensions of the input image (w*h = number of pixels)
`[out]`	dprev	average difference between current and previous iterations of the algorithm [in] repeatedRGB array of labels for the image pixels. Only one instance of each color has a label different from zero

This function is used in the main loop to decide whether further iterations are needed (if dprev is above a certain threshold)

Definition at line 845 of file colorfilteringIPOL.cpp.

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void delete_colorfiltering_data	(	struct RGBbin ***	check,
		struct infoPixel *	infopix,
		struct infoPixel *	infopixB
	)

free memory used to store temporary data structures

Definition at line 256 of file colorfilteringIPOL.cpp.

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void delete_colorfiltering_parameters ( struct paramColorFilter * param )

Delete input parameters data structure.

Definition at line 1151 of file colorfilteringIPOL.cpp.

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void delete_RGBdensities ( float *** dsts )

Delete data structure containing density values.

Definition at line 1247 of file colorfilteringIPOL.cpp.

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struct RGBpoint* find_neighboursRGB	(	float	R0,
		float	G0,
		float	B0,
		struct RGBbin ***	check,
		int	rneigh,
		int	nneighmax,
		int &	nneigh,
		int &	nneighdiff
	)			`[read]`

create a list of neighbors of a given RGB point (RGB points at L1-distance smaller than a threshold) in a color image

Parameters:

`[in]`	R0,G0,B0	initial RGB point
`[in]`	check	check[iR][iG][iB] is a pointer to a RGBbin data structure that contains the list of pixels whose color is in the range [iR, iR+1), [iG, iG+1), [iB, iB+1)
`[in]`	rneigh	threshold distance that defines the neighborhood around the initial RGB point
`[in]`	nneighmax	if nneighmax > 0, maximum number of different RGB points in the list, otherwise do not limit the size of the list
`[out]`	nneigh	number of color points in the list (each point appears as many times as pixels in the image have this color)
`[out]`	nneighdiff	number of diferent colors in the list (without taking into account the number of times it is repeated in the image)

The list is filled by looking for neighbors at L1-distances 0, 1, 2,..., rneigh, until at least nneighmax different colors are found (in the case that nneighmax > 0), or until the maximum distance rneigh is reached (in the case that nneighmax <= 0)

Returns:: pointer to the beginning of the list

Definition at line 376 of file colorfilteringIPOL.cpp.

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unsigned char find_projectionRGB	(	float	R0,
		float	G0,
		float	B0,
		struct RGBbin ***	check,
		struct infoProjection *	infoproj,
		int	rneigh,
		int	nneighmin,
		unsigned char	option
	)

find the projection of a given RGB point, from a color image, onto a locally defined line or plane

The list of neighbors (RGB points at L1-distance below some threshold) of the considered point is first computed. Each RGB point appears in the list as many times as it is found in the image (=number of pixels with the same RGB value), however the number of different RGB points is also computed. If the number of different RGB points is large enough then Principal Components Analysis is used to compute the line or plane that better fits the spatial distribution of RGB points. Finally the original point is projected onto this line or plane.

Parameters:

`[in]`	R0,G0,B0	initial RGB point
`[in]`	check	check[iR][iG][iB] is a pointer to a RGBbin data structure that contains the list of pixels whose color is in the range [iR, iR+1), [iG, iG+1), [iB, iB+1)
`[out]`	infoproj	data structure containing the parameters of the line or plane and the projection of the initial point
`[in]`	rneigh	threshold distance that defines the neighborhood of the initial RGB point
`[in]`	nneighmin	minimum number of different RGB points needed to perform PCA and compute projection
`[in]`	option	if option=2 compute plane, otherwise compute line

See also:: get_projectionRGB

Returns:: 0 if the point could not be projected, otherwise return 1 (projection onto line) o 2 (projection onto plane)

Definition at line 674 of file colorfilteringIPOL.cpp.

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void get_output_image	(	unsigned char *	outR,
		unsigned char *	outG,
		unsigned char *	outB,
		int	w,
		int	h,
		struct infoPixel *	infopix
	)

compute output image from updated RGB values

Parameters:

`[in]`	outR,outG,outB	color channels of the output image
`[in]`	w,h	dimensions of the output image
`[in]`	infopix	information about the colors of the pixel

Definition at line 939 of file colorfilteringIPOL.cpp.

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unsigned char get_projectionRGB	(	float	R0,
		float	G0,
		float	B0,
		struct RGBpoint *	firstneigh,
		struct infoProjection *	infoproj,
		unsigned char	option
	)

get parameters of a local line or a plane in the neighborhood of a given RGB point (use PCA) and project the point onto the line (plane)

The spatial distribution of the RGB points in the neighborhood of the considered point (L1-distance below a given threshold), including the point itself, is analyzed using Principal Components Analysis. For this analysis, the frequency of the color point (i.e. the number of times it appears in the image) is taken into account

The output line (or plane) is defined by the first (or two first) principal components and passes through the center of mass of the considered RGB points

See also:: compute_pca3

Parameters:

`[in]`	R0,G0,B0	initial RGB point
`[in]`	firstneigh	pointer to the list of neighbors of the input point
`[out]`	infoproj	data structure containing the parameters of the line or plane and the projection of the initial point
`[in]`	if	option=2 compute plane, otherwise compute line

Returns:: 1 if projection to a line, 2 if projection to a plane

Definition at line 550 of file colorfilteringIPOL.cpp.

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int initialize_colorfiltering_data	(	unsigned char *	R,
		unsigned char *	G,
		unsigned char *	B,
		int	w,
		int	h,
		struct RGBbin ****	checkOut,
		struct infoPixel **	infopixOut,
		struct infoPixel **	infopixBOut,
		int **	repeatedRGBOut,
		unsigned char	ignore000
	)

initialization of data structures for RGB cube processing

Parameters:

`[in]`	R,G,B	pointers to red, green and blue channels of the input image
`[out]`	checkOut	checkOut[iR][iG][iB] is a pointer to a RGBbin data structure that contains the list of pixels whose color is in the range [iR, iR+1), [iG, iG+1), [iB, iB+1)
`[out]`	infopixOut	infopixOut[k] is a pointer to a infoPixel data structure that contains information about the color of pixel k
`[out]`	infopixOutB	infopixOuBt[k] is a pointer to a infoPixel data structure that contains information about the color of pixel k
`[out]`	repeatedRGBOut	repeatedRGBOut[k] counts the number of occurrences of the color of p�xel k, provided that pixel k is the first occurrence of the color, else repeatedRGBOut[k]=0
`[in]`	ignore000	if ignore000=1 do not take into account pixels with (0, 0, 0) color (eventually excluded from processing after a preprocessing step)

Remark: Initially infopixOut and infopixOutB contain the same information, but as the algorithm iterates one of them is used to store the update information while the other keeps the old RGB values. Their role switches as the algorithm iterates.

Returns:: number of colors in the image (always number of colors <= number of pixels)

Definition at line 161 of file colorfilteringIPOL.cpp.

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struct paramColorFilter* new_colorfiltering_parameters	(	int	rneigh,
		int	rsim,
		int	nneighmin,
		float	eitmax,
		unsigned char	option,
		unsigned char	ignore000
	)			`[read]`

Organize input parameters in a data structure.

Parameters:

`[in]`	rneigh	distance defining the neighborhood of a color point (neighbors are RGB points at L1-distance below rneigh)
`[in]`	rsim	distance defining a small neighborhood around each color point, it is used to speed up the algorithm. It must be much smaller than rneigh, typically rsim=rneigh/3
`[in]`	nneighmin	minimum number of neighbors needed to compute a local line or plane in the vicinity of a color point
`[in]`	eitmax	stop criterion of the algorithm. The algorithm is iterated until the average difference of corresponding colors in two consecutive iterations is below eitmax
`[in]`	option	project points to lines (option=1) or planes (option=2)
`[in]`	ignore000	if set to 1, do not take into account pixels with (0,0,0) RGB value (eventually discarded for computation in a preprocessing step)

Returns:: Data structure containing the input parameters

Definition at line 1129 of file colorfilteringIPOL.cpp.

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void process_RGBpoint	(	float	R0,
		float	G0,
		float	B0,
		unsigned char	validprojection,
		struct RGBbin ***	check,
		struct infoPixel *	infopix,
		struct infoPixel *	infopixB,
		struct infoProjection *	infoproj,
		int	rsim
	)

update RGB values from the projection of initial RGB points onto local lines or planes

Parameters:

`[in]`	R0,G0,B0	initial RGB point
`[in]`	validprojection	label indicating whether the point is projected to a line (1), a plane (2) or is not projected at all (0)
`[in]`	check	check[iR][iG][iB] is a pointer to a RGBbin data structure that contains the list of pixels whose color is in the range [iR, iR+1), [iG, iG+1), [iB, iB+1)
`[in]`	infopix	information about the current colors of the pixels
`[out]`	infopixB	information about the updated colors of the pixels
`[out]`	infoproj	data structure containing the parameters of the line or plane and the projection of the initial point
`[in]`	rsim	speed up parameter, all the points in a neighborhood of radius rsim of a the initial color point are projected to the same line/plane

Definition at line 721 of file colorfilteringIPOL.cpp.

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void project_point	(	float	R0,
		float	G0,
		float	B0,
		float &	newR,
		float &	newG,
		float &	newB,
		float	Rcm,
		float	Gcm,
		float	Bcm,
		float	vx,
		float	vy,
		float	vz,
		unsigned char	option
	)

project RGB point onto a line or a plane

Parameters:

`[in]`	R0,G0,B0	coordinates of the initial RGB point
`[out]`	newR,newG,newB	coordinates of the projected point
`[in]`	Rcm,Gcm,Bcm	point coordinates of a point contained in the line or plane
`[in]`	vx,vy,vy	coordinates of the unitary direction vector of the line, or the orthonormal vector to the plane
`[in]`	option	option=1 project to line, otherwise project to plane

Definition at line 493 of file colorfilteringIPOL.cpp.

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void removeisolatedRGB	(	unsigned char *	R,
		unsigned char *	G,
		unsigned char *	B,
		unsigned char *	outR,
		unsigned char *	outG,
		unsigned char *	outB,
		int	w,
		int	h,
		int	r,
		int	nmin,
		int &	nRGB,
		int &	nisolatedRGB,
		int &	nisolatedpixels
	)

Filter out "isolated" colors in RGB space, that is, colors with a small number of neighbors.

The result is an image identical to the original, except at the pixels with "isolated" colors, whose value has been replace by (0, 0, 0). The number of neighbors of a pixel is the number of color points at L1-distance below some threshold. Each color appears in the list of neighbors as many times as it is present in the image (i.e. the frequency of the color is taken into account in the computations).

Parameters:

`[in]`	R,G,B	color channels of the input image
`[out]`	outR,outG,outB	color channels of the output image
`[in]`	w,h	dimensions of input and output images
`[in]`	r	radius of the neighborhood around each color point
`[in]`	nmin	threshold for the minimum number of neighboring color points needed to decide that a color is not "isolated"
`[out]`	nRGB	number of colors in input image
`[out]`	nisolatedRGB	number of "isolated" colors
`[out]`	nisolatedpixels	number of pixel with "isolated" color

Definition at line 1284 of file colorfilteringIPOL.cpp.

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void reset_color_info ( struct RGBbin *** check )

reset data structures for a new iteration of the filtering algorithm

Parameters:

[in] check check[iR][iG][iB] is a pointer to a RGBbin data structure that contains the list of pixels whose color is in the range [iR, iR+1), [iG, iG+1), [iB, iB+1)

Definition at line 809 of file colorfilteringIPOL.cpp.

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float*** RGBdensities	(	unsigned char *	R,
		unsigned char *	G,
		unsigned char *	B,
		int	w,
		int	h,
		int	rdst,
		float	hdst,
		float &	maxdst
	)

Compute the density of the colors of an image.

The density of a color C (in RGB space) is defined as

$\delta(C)=\sum_{C' \in {\cal S}} e^{-d(C, C')^2/h^2}$

where ${\cal S}$ is the set of neighbors of C $ d(C, C') $ is the Euclidean distance between colors C and C' in RGB space and $ h $ is a weighting parameter

The set of neighbors of a color C is composed of all the colors at L1-distance below some threshold $ r $ . Each color appears in the set of neighbors as many times as it is present in the image (i.e. the frequency of the color is taken into account in the computations). Tipically the weighting parameter is $h = r/\sqrt{2}$ so the weight of the furthest neighbors is $e^{-2}=0.135$

Parameters:

`[in]`	R,G,B	color channels of the image
`[in]`	w,h	dimensions of the image
`[in]`	rdst	radius of the neighbor around each color point
`[in]`	hdst	weighting parameter
`[out]`	maxdst	maximum density value

Returns:: density of each RGB point of the image

Definition at line 1186 of file colorfilteringIPOL.cpp.

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void update_color_info	(	struct RGBbin ***	check,
		struct infoPixel *	infopix,
		int	w,
		int	h
	)

update color information for a new iteration of the filtering algorithm

Parameters:

`[in]`	check	check[iR][iG][iB] is a pointer to a RGBbin data structure that contains the list of pixels whose color is in the range [iR, iR+1), [iG, iG+1), [iB, iB+1)
`[in]`	infopix	information about the colors of the pixel
`[in]`	w,h	dimensions of the input image (w*h = number of pixels)

Definition at line 884 of file colorfilteringIPOL.cpp.

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cppcode/colorfilteringIPOL.cpp File Reference

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