GlHistogram Class Reference

#include <ImFusion/GL/GlHistogram.h>

Provides an interface to calculate the histogram of an image either on the CPU or on the GPU. More...

Inheritance diagram for GlHistogram:

Detailed Description

Provides an interface to calculate the histogram of an image either on the CPU or on the GPU.

The GPU implementation supports two modes:

• If your hardware/driver combination supports OpenGL 4.3 (more precisely the ARB_shader_image_load_store and ARB_compute_shader extensions), GlHistogram will use OpenGL compute shaders.
• If your hardware/driver combination does not support OpenGL 4.3, GlHistogram will fall back to an OpenGL 3.3 implementation based on "Efficient Histogram Generation Using Scattering on GPUs" (Scheuermann, Hensley). Please be aware that this implementation is slower and may be less precise due to float arithmetic.

Usage Example:

GlHistogram histogrammer;
histogrammer.setBinCount(128);
histogrammer.setMinMaxIntensity(vec2{0.0, 42.0});
if (!histogrammer.update(img))
    return error();
const TypedImage<float>* histogram = histogrammer.typedData();

Note

• This class can calculate histograms for images with up to 4 channels.
• Due to using float as internal representation the histogram counts may become inaccurate or even saturate for values beyond 2^24.
• Due to the needed shaders and buffers, the instantiation of a GlHistogram instance is rather expensive. You should cache it if possible.

See also

HistogramDataComponent, GlJointHistogram

Public Types
enum	Device { Device_CPU = 0 , Device_GPU = 1 }

Public Member Functions
	GlHistogram ()
	Creates a new GlHistogram instance with default settings.

Configure Histogram Computation
int	binCount () const
	Returns the number of histogram bins.
void	setBinCount (int bins)
	Sets the number of histogram bins.
bool	mergesChannels () const
	Returns the flag whether to compute a single histogram of the averages over all channels or an individual histogram for each channel.
void	setMergeChannels (bool value)
	Sets the flag whether to compute a single histogram of the averages over all channels or an individual histogram for each channel.
vec2	minmaxIntensity () const
	Returns the minimum/maximum intensity to use during binning.
void	setMinmaxIntensity (vec2 value)
	Sets the minimum/maximum intensity to use during binning.

Run Histogram Computation
bool	update (SharedImage *image, Device device=Device_GPU, bool considerMask=false)
	Computes the histogram of the provided image and returns true on success.
bool	update (const GlImage *image, const GlMask *mask=nullptr)
	Computes the histogram of the provided image on the GPU and returns true on success.
bool	update (const MemImage *image, const Mask *mask=nullptr)
	Computes the histogram of the provided image on the CPU and returns true on success.

Access Results of the Computation
const SharedImage *	data () const
	Returns the histogram data as a 1D float image while maintaining its ownership.
const TypedImage< float > *	typedData () const
	Returns the histogram data as 1D float image while maintaining its ownership.
std::unique_ptr< SharedImage >	releaseData ()
	Returns the histogram data as a 1D float image and passes ownership of the returned pointer to the caller.
int	pixelCount (int channel=0) const
	Returns the total amount of pixels (sum of all bins) for the specified channel.
double	entropy (bool normalized=false, int channel=0)
	Return the image entropy based on the computed histogram.

Member Enumeration Documentation

Device

enum Device

Enumerator
Device_CPU	Compute the histogram on the CPU.
Device_GPU	Compute the histogram on the GPU, automatically detect OpenGL version to use.

Constructor & Destructor Documentation

GlHistogram()

GlHistogram

(

)

Creates a new GlHistogram instance with default settings.

Exceptions

std::runtime_error

if initialization of the OpenGL resources fails.

Member Function Documentation

minmaxIntensity()

vec2 minmaxIntensity

(

)

const

Returns the minimum/maximum intensity to use during binning.

If the minmax interval is empty (i.e. min == max) GlHistogram will use the following ranges during binning:

• Integral types: [std::numeric_limits<>::min(), std::numeric_limits<>::max()]
• Float types: [0, 1]

setMinmaxIntensity()

void setMinmaxIntensity

(

vec2

value

)

Sets the minimum/maximum intensity to use during binning.

If the minmax interval is empty (i.e. min == max) GlHistogram will use the following ranges during binning:

• Integral types: [std::numeric_limits<>::min(), std::numeric_limits<>::max()]
• Float types: [0, 1]

update() [1/3]

bool update	(	SharedImage *	image,
		Device	device = Device_GPU,
		bool	considerMask = false )

Computes the histogram of the provided image and returns true on success.

Parameters

image	Input image
device	Device to use for computation
considerMask	Flag whether to consider a Mask attached to the SharedImage during histogram computation

update() [2/3]

bool update	(	const GlImage *	image,
		const GlMask *	mask = nullptr )

Computes the histogram of the provided image on the GPU and returns true on success.

Parameters

image	Input image
mask	Optional GlMask to consider during during histogram computation

update() [3/3]

bool update	(	const MemImage *	image,
		const Mask *	mask = nullptr )

Computes the histogram of the provided image on the CPU and returns true on success.

Parameters

image	Input image
mask	Optional Mask to consider during during histogram computation

data()

const SharedImage * data

(

)

const

Returns the histogram data as a 1D float image while maintaining its ownership.

If the object was constructed with mergeChannels set to true, the data will be returned in a single channel image. If the object was constructed with mergeChannels set to false, the data will be returned in a 4-channel image.

entropy()

double entropy	(	bool	normalized = false,
		int	channel = 0 )

Return the image entropy based on the computed histogram.

Parameters

normalized

Normalize result with respect to number of bins (cf. Donath, Beckmann, 2006)

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

• ImFusion/GL/GlHistogram.h