ImageHistogram

ImageHistogram[image]

plots a histogram of the pixel levels for each channel in image.

ImageHistogram[image,bspec]

uses bin specification bspec.

ImageHistogram[image,bspec,range]

plots the histogram of the pixel values in the given range.

Details and Options

An image histogram is a graphical representation of the color distribution in an image.

ImageHistogram works with arbitrary grayscale and multichannel 2D and 3D images.
For RGB images, ImageHistogram by default displays the channels using red, green, and blue.
Binning specification bspec can be any of the following:

	n	n equally spaced bins
	Automatic	automatic choice of binning
	All	return tally of all available pixel values
	"Byte"	256 levels after converting data values to a "Byte" type

By default, for binary images two bins are used; otherwise, 128 bins are used.
The range can be of the following forms:

	Automatic	automatic ranges depending on the color space
	All	include all values
	{All,max}	include values below max
	{min,All}	include values above min
	{min,max}	include values between min and max

The following defaults are used for range depending on the image color space. The ranges are chosen to include the subspace of the "RGB" color space.
"Grayscale","RGB","CMYK","HSB" {0,1}

"XYZ" {0,1}

"LAB" {-1.13,1}

"LCH" {0,1.3}

"LUV" {-1.26,1.76}
ImageHistogram accepts options of ListPlot, with the following additions and changes: [List of all options]

Appearance	Automatic	detailed appearance of the histogram
AspectRatio	1/3	ratio of height to width
Axes	False	whether to draw axes
Filling	Axis	how to fill in stems for each point
Frame	True	whether to include a frame
FrameTicks	None	frame ticks
InterpolationOrder	0	the polynomial degree of curves used in joining data points
Joined	True	whether to join bars
Method	"IncludeOutOfRange"	method to use
PlotRangePadding	None	how much to pad the range of values

Possible settings for Appearance are:

	"RGB"	show RGB channel values and overlapping colors
	"Separated"	make separate histograms for each channel
	"Stacked"	stack values for each channel
	"Transparent"	show channels overlapping, using transparency

Possible settings for Method include:
"IncludeOutOfRange" values below range in first bin and values above range in last bin

"ExcludeOutOfRange" do not count out-of-range values

List of all options

AlignmentPoint	Center	the default point in the graphic to align with
Appearance	Automatic	detailed appearance of the histogram
AspectRatio	1/3	ratio of height to width
Axes	False	whether to draw axes
AxesLabel	None	axes labels
AxesOrigin	Automatic	where axes should cross
AxesStyle	{}	style specifications for the axes
Background	None	background color for the plot
BaselinePosition	Automatic	how to align with a surrounding text baseline
BaseStyle	{}	base style specifications for the graphic
ContentSelectable	Automatic	whether to allow contents to be selected
CoordinatesToolOptions	Automatic	detailed behavior of the coordinates tool
DataRange	Automatic	the range of x values to assume for data
Epilog	{}	primitives rendered after the main plot
Filling	Axis	how to fill in stems for each point
FillingStyle	Automatic	style to use for filling
FormatType	TraditionalForm	the default format type for text
Frame	True	whether to include a frame
FrameLabel	None	frame labels
FrameStyle	{}	style specifications for the frame
FrameTicks	None	frame ticks
FrameTicksStyle	{}	style specifications for frame ticks
GridLines	None	grid lines to draw
GridLinesStyle	{}	style specifications for grid lines
ImageMargins	0.	the margins to leave around the graphic
ImagePadding	All	what extra padding to allow for labels etc.
ImageSize	Automatic	the absolute size at which to render the graphic
InterpolationOrder	0	the polynomial degree of curves used in joining data points
IntervalMarkers	Automatic	how to render uncertainty
IntervalMarkersStyle	Automatic	style for uncertainty elements
Joined	True	whether to join bars
LabelingFunction	Automatic	how to label points
LabelingSize	Automatic	maximum size of callouts and labels
LabelStyle	{}	style specifications for labels
Method	"IncludeOutOfRange"	method to use
MultiaxisArrangement	None	how to arrange multiple axes for data
PerformanceGoal	$PerformanceGoal	aspects of performance to try to optimize
PlotHighlighting	Automatic	highlighting effect for curves
PlotLabel	None	overall label for the plot
PlotLabels	None	labels for data
PlotLayout	"Overlaid"	how to position data
PlotLegends	None	legends for data
PlotMarkers	None	markers to use to indicate each point
PlotRange	Automatic	range of values to include
PlotRangeClipping	True	whether to clip at the plot range
PlotRangePadding	None	how much to pad the range of values
PlotRegion	Automatic	the final display region to be filled
PlotStyle	Automatic	graphics directives to determine styles of points
PlotTheme	$PlotTheme	overall theme for the plot
PreserveImageOptions	Automatic	whether to preserve image options when displaying new versions of the same graphic
Prolog	{}	primitives rendered before the main plot
RotateLabel	True	whether to rotate y labels on the frame
ScalingFunctions	None	how to scale individual coordinates
TargetUnits	Automatic	units to display in the plot
Ticks	Automatic	axes ticks
TicksStyle	{}	style specifications for axes ticks

Examples

open allclose all

Basic Examples (3)

Histogram of an RGB image:

Histogram of a grayscale image:

Histogram of a 3D volume:

Scope (6)

Specify the number of levels:

Histogram of a grayscale image showing all distinct levels:

Use range specification All to plot the histogram from the minimum to maximum value in the image:

Histogram of a binary image:

Use a range specification that includes negative values for plotting the histogram:

Histogram of a CMYK image:

Options (10)

Appearance (2)

Use additive colors to represent overlapping regions of histograms of an RGB image:

Show separate histograms for each color channel:

Stack the color channels vertically:

For non-RGB images, default plotting colors are used for all appearances:

Transparent histogram of a Lab image:

Stacked histogram:

Separated histogram:

InterpolationOrder (2)

By default, the histogram is plotted with interpolation of order :

Create a smooth histogram of an image:

Joined (1)

Render histogram using a stem plot:

Use a disjoint histogram:

Method (1)

Control how pixels outside of the histogram range are counted and displayed:

PlotRange (1)

Use PlotRange->Automatic for automatically determining the plot range:

PlotRange->All includes the entire histogram:

Modify the plot range to better visualize the distribution of higher intensities:

PlotTheme (3)

Use a theme minimum styling:

Add horizontal grid lines to the plot:

Use a theme with dark background in a high-contrast color scheme:

Applications (1)

Use the image histograms to estimate a suitable threshold:

Select threshold value using visual inspection of histograms:

Binarize image using selected threshold:

Properties & Relations (3)

Image histogram can also be computed using Histogram; however, it is slower:

Find the histogram distribution of an image:

ImageHistogram blends alpha channel with black:

Blend with black before computing the histogram:

Blend with white:

Drop the alpha channel:

Possible Issues (1)

Histograms with varying bin widths cannot be displayed using the "Stacked" appearance:

Use a different appearance:

Interactive Examples (1)

Interactive histogram of an RGB image:

Neat Examples (1)

Histogram of an image that is made progressively darker: