Brightness and contrast adjustment

Functions
VISP_EXPORT void	vp::clahe (const vpImage< unsigned char > &I1, vpImage< unsigned char > &I2, int blockRadius=150, int bins=256, float slope=3.0f, bool fast=true)
VISP_EXPORT void	vp::clahe (const vpImage< vpRGBa > &I1, vpImage< vpRGBa > &I2, int blockRadius=150, int bins=256, float slope=3.0f, bool fast=true)
VISP_EXPORT void	vp::adjust (vpImage< unsigned char > &I, double alpha, double beta)
VISP_EXPORT void	vp::adjust (const vpImage< unsigned char > &I1, vpImage< unsigned char > &I2, double alpha, double beta)
VISP_EXPORT void	vp::adjust (vpImage< vpRGBa > &I, const double alpha, double beta)
VISP_EXPORT void	vp::adjust (const vpImage< vpRGBa > &I1, vpImage< vpRGBa > &I2, double alpha, double beta)

Detailed Description

Brightness and contrast adjustment.

Function Documentation

adjust() [1/4]

void vp::adjust	(	vpImage< unsigned char > &	I,
		double	alpha,
		double	beta
	)

Adjust the brightness of a grayscale image such as the new intensity is alpha x old_intensity + beta.

Parameters

I	: The grayscale image to adjust the brightness.
alpha	: Multiplication coefficient.
beta	: Constant value added to the old intensity.

Examples:

testImgproc.cpp, and tutorial-brightness-adjustment.cpp.

Definition at line 81 of file vpImgproc.cpp.

References vpImage< Type >::performLut().

Referenced by vp::adjust().

adjust() [2/4]

void vp::adjust	(	const vpImage< unsigned char > &	I1,
		vpImage< unsigned char > &	I2,
		double	alpha,
		double	beta
	)

Adjust the brightness of a grayscale image such as the new intensity is alpha x old_intensity + beta.

Parameters

I1	: The original grayscale image.
I2	: The grayscale image after adjusting pixel intensities.
alpha	: Multiplication coefficient.
beta	: Constant value added to the old intensity.

Definition at line 104 of file vpImgproc.cpp.

References vp::adjust().

adjust() [3/4]

void vp::adjust	(	vpImage< vpRGBa > &	I,
		const double	alpha,
		double	beta
	)

Adjust the brightness of a color image such as the new intensity is alpha x old_intensity + beta.

Parameters

I	: The color image to adjust the brightness.
alpha	: Multiplication coefficient.
beta	: Constant value added to the old intensity.

Definition at line 122 of file vpImgproc.cpp.

References vpRGBa::A, vpRGBa::B, vpRGBa::G, vpImage< Type >::performLut(), and vpRGBa::R.

adjust() [4/4]

void vp::adjust	(	const vpImage< vpRGBa > &	I1,
		vpImage< vpRGBa > &	I2,
		double	alpha,
		double	beta
	)

Adjust the brightness of a color image such as the new intensity is alpha x old_intensity + beta.

Parameters

I1	: The original color image.
I2	: The color image after adjusting pixel intensities.
alpha	: Multiplication coefficient.
beta	: Constant value added to the old intensity.

Definition at line 148 of file vpImgproc.cpp.

References vp::adjust().

clahe() [1/2]

void vp::clahe	(	const vpImage< unsigned char > &	I1,
		vpImage< unsigned char > &	I2,
		int	blockRadius = 150,
		int	bins = 256,
		float	slope = 3.0f,
		bool	fast = true
	)

Adjust the contrast of a grayscale image locally using the Contrast Limited Adaptative Histogram Equalization method. The limit parameter allows to limit the slope of the transformation function to prevent the overamplification of noise. This method is a transcription of the CLAHE ImageJ plugin code by Stephan Saalfeld.

Parameters

I1	: The first grayscale image.
I2	: The second grayscale image after application of the CLAHE method.
blockRadius	: The size (2*blockRadius+1) of the local region around a pixel for which the histogram is equalized. This size should be larger than the size of features to be preserved.
bins	: The number of histogram bins used for histogram equalization (between 1 and 256). The number of histogram bins should be smaller than the number of pixels in a block.
slope	: Limits the contrast stretch in the intensity transfer function. Very large values will let the histogram equalization do whatever it wants to do, that is result in maximal local contrast. The value 1 will result in the original image.
fast	: Use the fast but less accurate version of the filter. The fast version does not evaluate the intensity transfer function for each pixel independently but for a grid of adjacent boxes of the given block size only and interpolates for locations in between.

Examples:

testImgproc.cpp, and tutorial-contrast-sharpening.cpp.

Definition at line 228 of file vpCLAHE.cpp.

References vpImage< Type >::getHeight(), vpImage< Type >::getWidth(), and vpImage< Type >::resize().

Referenced by vp::clahe().

clahe() [2/2]

void vp::clahe	(	const vpImage< vpRGBa > &	I1,
		vpImage< vpRGBa > &	I2,
		int	blockRadius = 150,
		int	bins = 256,
		float	slope = 3.0f,
		bool	fast = true
	)

Adjust the contrast of a color image locally using the Contrast Limited Adaptative Histogram Equalization method. The limit parameter allows to limit the slope of the transformation function to prevent the overamplification of noise. This method is a transcription of the CLAHE ImageJ plugin code by Stephan Saalfeld.

Parameters

I1	: The first color image.
I2	: The second color image after application of the CLAHE method.
blockRadius	: The size (2*blockRadius+1) of the local region around a pixel for which the histogram is equalized. This size should be larger than the size of features to be preserved.
bins	: The number of histogram bins used for histogram equalization (between 1 and 256). The number of histogram bins should be smaller than the number of pixels in a block.
slope	: Limits the contrast stretch in the intensity transfer function. Very large values will let the histogram equalization do whatever it wants to do, that is result in maximal local contrast. The value 1 will result in the original image.
fast	: Use the fast but less accurate version of the filter. The fast version does not evaluate the intensity transfer function for each pixel independently but for a grid of adjacent boxes of the given block size only and interpolates for locations in between.

Definition at line 493 of file vpCLAHE.cpp.

References vpImage< Type >::bitmap, vp::clahe(), vpImage< Type >::getHeight(), vpImage< Type >::getWidth(), vpImage< Type >::resize(), and vpImageConvert::split().