ImageDev

HistogramEqualization

Enhances the contrast of an image by performing an histogram equalization.

Access to parameter description

This algorithm performs an histogram equalization of image $I$ onto image $O$. For example, if an image contains $N$ pixels and uses $M$ gray values, there is an average of $N/M$ pixels per gray level. An image is correctly contrasted if the number of pixels is close to this mean value for each gray level value.

The aim of histogram equalization is to transform the histogram to make it uniform. In Figure 1-a, the histogram is very condensed, and the image is poorly contrasted.
In Figure 1-b, the histogram is more widely distributed, and the image has better contrast.

<b> Figure 1.</b> Histogram equalization
Figure 1. Histogram equalization


See also

Function Syntax

This function returns outputImage. 
// Function prototype
std::shared_ptr< iolink::ImageView >
histogramEqualization( std::shared_ptr< iolink::ImageView > inputImage,
                       HistogramEqualization::RangeMode rangeMode,
                       iolink::Vector2i32 intensityInputRange,
                       iolink::Vector2i32 intensityOutputRange,
                       std::shared_ptr< iolink::ImageView > outputImage = NULL );
This function returns outputImage. 
// Function prototype.
histogram_equalization( input_image,
                        range_mode = HistogramEqualization.RangeMode.MIN_MAX,
                        intensity_input_range = [0, 255],
                        intensity_output_range = [0, 255],
                        output_image = None )
This function returns outputImage. 
// Function prototype.
public static IOLink.ImageView
HistogramEqualization( IOLink.ImageView inputImage,
                       HistogramEqualization.RangeMode rangeMode = ImageDev.HistogramEqualization.RangeMode.MIN_MAX,
                       int[] intensityInputRange = null,
                       int[] intensityOutputRange = null,
                       IOLink.ImageView outputImage = null );

Class Syntax

Parameters

Parameter Name Description Type Supported Values Default Value
input
inputImage
The input image to enhance. Image Binary, Label or Grayscale nullptr
input
rangeMode
The way to define the input intensity range.
MIN_MAX The input intensity range is between the minimum and the maximum of the image intensities.
OTHER The input intensity range is between user-defined bounds [a,b].
Enumeration MIN_MAX
input
intensityInputRange
The input intensity range [a, b] to use when the range mode is set to OTHER. This parameter is ignored with the MIN_MAX range mode. Vector2i32 >=0 {0, 255}
input
intensityOutputRange
The output intensity range. Vector2i32 >=0 {0, 255}
output
outputImage
The output image. Its dimensions and type are forced to the same values as the input. Image nullptr
Parameter Name Description Type Supported Values Default Value
input
input_image
The input image to enhance. image Binary, Label or Grayscale None
input
range_mode
The way to define the input intensity range.
MIN_MAX The input intensity range is between the minimum and the maximum of the image intensities.
OTHER The input intensity range is between user-defined bounds [a,b].
enumeration MIN_MAX
input
intensity_input_range
The input intensity range [a, b] to use when the range mode is set to OTHER. This parameter is ignored with the MIN_MAX range mode. vector2i32 >=0 [0, 255]
input
intensity_output_range
The output intensity range. vector2i32 >=0 [0, 255]
output
output_image
The output image. Its dimensions and type are forced to the same values as the input. image None
Parameter Name Description Type Supported Values Default Value
input
inputImage
The input image to enhance. Image Binary, Label or Grayscale null
input
rangeMode
The way to define the input intensity range.
MIN_MAX The input intensity range is between the minimum and the maximum of the image intensities.
OTHER The input intensity range is between user-defined bounds [a,b].
Enumeration MIN_MAX
input
intensityInputRange
The input intensity range [a, b] to use when the range mode is set to OTHER. This parameter is ignored with the MIN_MAX range mode. Vector2i32 >=0 {0, 255}
input
intensityOutputRange
The output intensity range. Vector2i32 >=0 {0, 255}
output
outputImage
The output image. Its dimensions and type are forced to the same values as the input. Image null

Object Examples

auto foam = readVipImage( std::string( IMAGEDEVDATA_IMAGES_FOLDER ) + "foam.vip" );

HistogramEqualization histogramEqualizationAlgo;
histogramEqualizationAlgo.setInputImage( foam );
histogramEqualizationAlgo.setRangeMode( HistogramEqualization::RangeMode::MIN_MAX );
histogramEqualizationAlgo.setIntensityInputRange( {0, 255} );
histogramEqualizationAlgo.setIntensityOutputRange( {0, 255} );
histogramEqualizationAlgo.execute();

std::cout << "outputImage:" << histogramEqualizationAlgo.outputImage()->toString();

foam = imagedev.read_vip_image(imagedev_data.get_image_path("foam.vip"))

histogram_equalization_algo = imagedev.HistogramEqualization()
histogram_equalization_algo.input_image = foam
histogram_equalization_algo.range_mode = imagedev.HistogramEqualization.MIN_MAX
histogram_equalization_algo.intensity_input_range = [0, 255]
histogram_equalization_algo.intensity_output_range = [0, 255]
histogram_equalization_algo.execute()

print( "output_image:", str( histogram_equalization_algo.output_image ) )

ImageView foam = Data.ReadVipImage( @"Data/images/foam.vip" );

HistogramEqualization histogramEqualizationAlgo = new HistogramEqualization
{
    inputImage = foam,
    rangeMode = HistogramEqualization.RangeMode.MIN_MAX,
    intensityInputRange = new int[]{0, 255},
    intensityOutputRange = new int[]{0, 255}
};
histogramEqualizationAlgo.Execute();

Console.WriteLine( "outputImage:" + histogramEqualizationAlgo.outputImage.ToString() );

Function Examples

auto foam = readVipImage( std::string( IMAGEDEVDATA_IMAGES_FOLDER ) + "foam.vip" );

auto result = histogramEqualization( foam, HistogramEqualization::RangeMode::MIN_MAX, {0, 255}, {0, 255} );

std::cout << "outputImage:" << result->toString();

foam = imagedev.read_vip_image(imagedev_data.get_image_path("foam.vip"))

result = imagedev.histogram_equalization( foam, imagedev.HistogramEqualization.MIN_MAX, [0, 255], [0, 255] )

print( "output_image:", str( result ) )

ImageView foam = Data.ReadVipImage( @"Data/images/foam.vip" );

IOLink.ImageView result = Processing.HistogramEqualization( foam, HistogramEqualization.RangeMode.MIN_MAX, new int[]{0, 255}, new int[]{0, 255} );

Console.WriteLine( "outputImage:" + result.ToString() );