org.openimaj.image.processing.edges

Class StrokeWidthTransform

java.lang.Object

org.openimaj.image.processing.edges.StrokeWidthTransform

All Implemented Interfaces:

ImageProcessor<FImage>, Processor<FImage>, SinglebandImageProcessor<Float,FImage>

@Reference(type=Inproceedings,
           author={"Epshtein, B.","Ofek, E.","Wexler, Y."},
           title="Detecting text in natural scenes with stroke width transform",
           year="2010",
           booktitle="Computer Vision and Pattern Recognition (CVPR), 2010 IEEE Conference on",
           pages={"2963","2970"},
           customData={"keywords","image processing;text analysis;image operator;image pixel;natural images;natural scenes;stroke width transform;text detection;Colored noise;Computer vision;Engines;Filter bank;Geometry;Image segmentation;Layout;Optical character recognition software;Pixel;Robustness","doi","10.1109/CVPR.2010.5540041","ISSN","1063-6919"})
public class StrokeWidthTransform
extends Object
implements SinglebandImageProcessor<Float,FImage>

Implementation of the Stroke Width Transform.

The Stroke Width Transform detects strokes and their respective widths from an image. This implementation contains a number of enhancements to improve the quality of the detected strokes, based on ideas from LibCCV implementation:

• We search around the stroke in a small window for endpoints.
• We search around the endpoint in a small window for matching gradients.
• In addition to the stroke along the gradient, we also stroke at +/-45 degrees from this.

Author:

Jonathon Hare (jsh2@ecs.soton.ac.uk)

Nested Class Summary

Nested classes/interfaces inherited from interface org.openimaj.image.processor.SinglebandImageProcessor

SinglebandImageProcessor.Processable<T,S extends Image<T,S>,I extends Image<?,I>>

Constructor Summary

Constructors

Constructor and Description
StrokeWidthTransform(boolean direction, CannyEdgeDetector canny) Construct the SWT with the given Canny edge detector.
StrokeWidthTransform(boolean direction, float sigma) Construct the SWT with the given sigma for smoothing in the Canny phase The Canny thresholds are chosen automatically.
StrokeWidthTransform(boolean direction, float lowThresh, float highThresh, float sigma) Construct with all Canny parameters set manually.

Method Summary

Modifier and Type	Method and Description
boolean	getDirection() Get the direction of the SWT; true for dark on light, false for light
int	getMaxStrokeWidth() Get the maximum stroke width
static FImage	normaliseImage(FImage input) Normalise the output image of the StrokeWidthTransform for display.
void	processImage(FImage image) Process an image.
void	setDirection(boolean direction) Set the direction of the SWT; true for dark on light, false for light
void	setMaxStrokeWidth(int maxStrokeWidth) Set the maximum stroke width

Methods inherited from class java.lang.Object

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

Constructor Detail

StrokeWidthTransform

public StrokeWidthTransform(boolean direction,
                            CannyEdgeDetector canny)

Construct the SWT with the given Canny edge detector.

Parameters:

direction - direction of the SWT; true for dark on light, false for light on dark.

canny - the canny edge detector

StrokeWidthTransform

public StrokeWidthTransform(boolean direction,
                            float sigma)

Construct the SWT with the given sigma for smoothing in the Canny phase The Canny thresholds are chosen automatically.

Parameters:

direction - direction of the SWT; true for dark on light, false for light on dark.

sigma - the amount of initial blurring

StrokeWidthTransform

public StrokeWidthTransform(boolean direction,
                            float lowThresh,
                            float highThresh,
                            float sigma)

Construct with all Canny parameters set manually.

Parameters:

direction - direction of the SWT; true for dark on light, false for light on dark.

lowThresh - lower hysteresis threshold.

highThresh - upper hysteresis threshold.

sigma - the amount of initial blurring.

Method Detail

getMaxStrokeWidth

public int getMaxStrokeWidth()

Get the maximum stroke width

Returns:

the maximum stroke width

setMaxStrokeWidth

public void setMaxStrokeWidth(int maxStrokeWidth)

Set the maximum stroke width

Parameters:

maxStrokeWidth - the maximum stroke width

processImage

public void processImage(FImage image)

Description copied from interface: ImageProcessor

Process an image. Implementing classes must alter the image passed in-place or assign the output to the input using Image.internalAssign(Image).

Specified by:

processImage in interface ImageProcessor<FImage>

Parameters:

image - The image to process in place.

normaliseImage

public static FImage normaliseImage(FImage input)

Normalise the output image of the StrokeWidthTransform for display. This replaces all Float.POSITIVE_INFINITY pixels with a value of 1, and min-max normalises all the valid stroke pixels to be between 0 and 1.

Parameters:

input - the image to normalise

Returns:

the normalised image

getDirection

public boolean getDirection()

Get the direction of the SWT; true for dark on light, false for light

Returns:

the direction

setDirection

public void setDirection(boolean direction)

Set the direction of the SWT; true for dark on light, false for light

Parameters:

direction - the direction to set