Package boofcv.alg.filter.binary

Class ThresholdNiblackFamily

java.lang.Object

boofcv.alg.filter.binary.ThresholdNiblackFamily

All Implemented Interfaces:

InputToBinary<GrayF32>

Direct Known Subclasses:

ThresholdNiblackFamily_MT

public class ThresholdNiblackFamily
extends Object
implements InputToBinary<GrayF32>

Several related algorithms based off the Niblack's [1] paper which are intended for use in thresholding images as a preprocessing step for OCR. All algorithms are based on local image statistics.

1. Niblack: T(x,y) = m(x,y) * [ 1 + k * (s(x,y)/R - 1)]
2. Sauvola: T(x,y) = m(x,y) * [ 1 + k * (s(x,y)/R - 1)]
3. Wolf-Jolion: T(x,y) = m(x,y) * [ 1 + k * (s(x,y)/R - 1)]

where T(x,y) is the pixel's threshold, m(x,y) is the local mean, s(x,y) is the local deviation, R is dynamic range of standard deviation, and k is a user specified threshold.

There are two tuning parameters 'k' a positive number and the the 'radius' of the local region. Recommended values:

• Niblack: k=0.3 and radius=15
• Sauvola: k=0.3 and radius=15
• Wolf-Jolion: k=0.5 and radius=15

[1] W.Niblack, An Introduction to Digital Image Processing. Prentice Hall, Englewood Cliffs, (1986).
[2] Sauvola, Jaakko, and Matti Pietikäinen. "Adaptive document image binarization." Pattern recognition 33.2 (2000): 225-236.
[3] C. Wolf, J-M. Jolion, “Extraction and Recognition of Artificial Text in Multimedia Documents”, Pattern Analysis and Applications, 6(4):309-326, (2003)

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static enum	ThresholdNiblackFamily.Variant	Which variant of this family is computed

Constructor Summary

Constructors

Constructor	Description
ThresholdNiblackFamily(ConfigLength width, float k, boolean down, ThresholdNiblackFamily.Variant variant)	Configures the algorithm.

Method Summary

Modifier and Type	Method	Description
protected void	applyThresholding(GrayF32 input, GrayU8 output)
ImageType<GrayF32>	getInputType()
void	process(GrayF32 input, GrayU8 output)	Converts the input image into a binary image.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

ThresholdNiblackFamily

public ThresholdNiblackFamily(ConfigLength width,
 float k,
 boolean down,
 ThresholdNiblackFamily.Variant variant)

Configures the algorithm.

Parameters:

width - size of local region. Try 31

k - User specified threshold adjustment factor. Must be positive. Try 0.3

down - Threshold down or up

Method Details

process

public void process(GrayF32 input,
 GrayU8 output)

Converts the input image into a binary image.

Specified by:

process in interface InputToBinary<GrayF32>

Parameters:

input - Input image. Not modified.

output - Output binary image. Modified.

applyThresholding

protected void applyThresholding(GrayF32 input,
 GrayU8 output)

getInputType

public ImageType<GrayF32> getInputType()

Specified by:

getInputType in interface InputToBinary<GrayF32>