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BoofCV is an open source Java library for real-time computer vision and robotics applications.
/*
* Copyright (c) 2011-2019, Peter Abeles. All Rights Reserved.
*
* This file is part of BoofCV (http://boofcv.org).
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package boofcv.alg.shapes.polygon;
import boofcv.alg.shapes.edge.SnapToLineEdge;
import boofcv.struct.distort.PixelTransform;
import boofcv.struct.image.ImageGray;
import georegression.geometry.UtilLine2D_F64;
import georegression.metric.Intersection2D_F64;
import georegression.struct.line.LineGeneral2D_F64;
import georegression.struct.point.Point2D_F32;
import georegression.struct.point.Point2D_F64;
import georegression.struct.shapes.Polygon2D_F64;
/**
*
* Improves the fits of a polygon's which is darker or lighter than the background. Info's edges are
* assumed to be perfectly straight lines. The edges are processed individually and fit to a line using weighted
* regression. Both black squares with white backgrounds and white shapes with black backgrounds can be found.
* The edges are selected to maximize the difference between light and dark regions.
*
*
* For example, assume an image axis aligned rectangle has a lower extent of 1,2 and a upper extent of 12,15, is
* entirely filled, excluding the upper extent pixels (as is typical). Then the found lower and upper extends of the
* found polygon will also be 1,2 and 12,15.
*
*
*
* If a line lies entirely along the image border it is not modified. If part of it lies along the image then only
* points not near the border are used to optimize its location.
*
*
* For input polygons which are in undistorted coordinates by with a distorted image call {@link #getSnapToEdge()}
* and invoke {@link SnapToLineEdge#setTransform(PixelTransform)}.
*
* @author Peter Abeles
*/
public class RefinePolygonToGrayLine> implements RefinePolygonToGray {
// How far away from a corner will it sample the line
private double cornerOffset = 2.0;
// maximum number of iterations
private int maxIterations = 10;
// convergence tolerance in pixels
private double convergeTolPixels = 0.01;
// The maximum number of pixels a corner can move in a single iteration
// designed to prevent divergence
private double maxCornerChangePixel=2;
private SnapToLineEdge snapToEdge;
//---------- storage for local work space
private LineGeneral2D_F64 general[] = new LineGeneral2D_F64[0]; // estimated line for each side
private Polygon2D_F64 previous;
// adjusted corner points which have been offset from the true corners
private Point2D_F64 adjA = new Point2D_F64();
private Point2D_F64 adjB = new Point2D_F64();
// the input image
protected T image;
private Class imageType;
// work space for checking to see if the line estimate diverged
private Point2D_F64 tempA = new Point2D_F64();
private Point2D_F64 tempB = new Point2D_F64();
private LineGeneral2D_F64 before = new LineGeneral2D_F64();
/**
* Constructor which provides full access to all parameters. See code documents
* value a description of these variables.
*
*/
public RefinePolygonToGrayLine(double cornerOffset, int lineSamples, int sampleRadius,
int maxIterations, double convergeTolPixels, double maxCornerChangePixel,
Class imageType ) {
this.cornerOffset = cornerOffset;
this.maxIterations = maxIterations;
this.convergeTolPixels = convergeTolPixels;
this.maxCornerChangePixel = maxCornerChangePixel;
this.snapToEdge = new SnapToLineEdge<>(lineSamples, sampleRadius, imageType);
this.imageType = imageType;
previous = new Polygon2D_F64(1);
}
/**
* Simplified constructor which uses reasonable default values for most variables
* @param numSides Number of sides on the polygon
* @param imageType Type of input image it processes
*/
public RefinePolygonToGrayLine(int numSides , Class imageType) {
previous = new Polygon2D_F64(numSides);
this.imageType = imageType;
this.snapToEdge = new SnapToLineEdge<>(20, 1, imageType);
}
/**
* Sets the image which is going to be processed. If a transform is to be used
* {@link SnapToLineEdge#setTransform} should be called before this.
*/
@Override
public void setImage(T image) {
this.image = image;
this.snapToEdge.setImage(image);
}
@Override
public void setLensDistortion(int width, int height, PixelTransform distToUndist, PixelTransform undistToDist) {
this.snapToEdge.setTransform(undistToDist);
}
@Override
public void clearLensDistortion() {
this.snapToEdge.setTransform(null);
}
/**
* Refines the fit a polygon by snapping it to the edges.
*
* @param input (input) Initial estimate for the polygon. CW or CCW ordering doesn't matter.
* @param output (output) the fitted polygon
*/
@Override
public boolean refine(Polygon2D_F64 input, Polygon2D_F64 output)
{
if( input.size() != output.size())
throw new IllegalArgumentException("Input and output sides do not match. "+input.size()+" "+output.size());
// sanity check input. If it's too small this algorithm won't work
if( checkShapeTooSmall(input) )
return false;
// see if this work space needs to be resized
if( general.length < input.size() ) {
general = new LineGeneral2D_F64[input.size() ];
for (int i = 0; i < general.length; i++) {
general[i] = new LineGeneral2D_F64();
}
}
// estimate line equations
return optimize(input,output);
}
/**
* Looks at the distance between each vertex. If that distance is so small the edge can't be measured the
* return true.
* @param input polygon
* @return true if too small or false if not
*/
private boolean checkShapeTooSmall(Polygon2D_F64 input) {
// must be longer than the border plus some small fudge factor
double minLength = cornerOffset*2 + 2;
for (int i = 0; i < input.size(); i++) {
int j = (i+1)%input.size();
Point2D_F64 a = input.get(i);
Point2D_F64 b = input.get(j);
if( a.distance2(b) < minLength*minLength )
return true;
}
return false;
}
/**
* Refines the initial line estimates using EM. The number of iterations is fixed.
*/
protected boolean optimize(Polygon2D_F64 seed , Polygon2D_F64 current ) {
previous.set(seed);
// pixels squares is faster to compute
double convergeTol = convergeTolPixels*convergeTolPixels;
// initialize the lines since they are used to check for corner divergence
for (int i = 0; i < seed.size(); i++) {
int j = (i + 1) % seed.size();
Point2D_F64 a = seed.get(i);
Point2D_F64 b = seed.get(j);
UtilLine2D_F64.convert(a,b,general[i]);
}
boolean changed = false;
for (int iteration = 0; iteration < maxIterations; iteration++) {
// snap each line to the edge independently. Lines will be in local coordinates
for (int i = 0; i < previous.size(); i++) {
int j = (i + 1) % previous.size();
Point2D_F64 a = previous.get(i);
Point2D_F64 b = previous.get(j);
before.set(general[i]);
boolean failed = false;
if( !optimize(a,b,general[i]) ) {
failed = true;
} else {
int k = (i+previous.size()-1) %previous.size();
// see if the corner has diverged
if( Intersection2D_F64.intersection(general[k], general[i],tempA) != null &&
Intersection2D_F64.intersection(general[i], general[j],tempB) != null ) {
if( tempA.distance(a) > maxCornerChangePixel || tempB.distance(b) > maxCornerChangePixel ) {
failed = true;
}
} else {
failed = true;
}
}
// The line fit failed. Probably because its along the image border. Revert it
if( failed ) {
general[i].set(before);
} else {
changed = true;
}
}
// Find the corners of the quadrilateral from the lines
if( !UtilShapePolygon.convert(general,current) )
return false;
// see if it has converged
boolean converged = true;
for (int i = 0; i < current.size(); i++) {
if( current.get(i).distance2(previous.get(i)) > convergeTol ) {
converged = false;
break;
}
}
if( converged ) {
// System.out.println("Converged early at "+iteration);
break;
} else {
previous.set(current);
}
}
return changed;
}
/**
* Fits a line defined by the two points. When fitting the line the weight of the edge is used to determine
* how influential the point is
* @param a Corner point in image coordinates.
* @param b Corner point in image coordinates.
* @param found (output) Line in image coordinates
* @return true if successful or false if it failed
*/
protected boolean optimize( Point2D_F64 a , Point2D_F64 b , LineGeneral2D_F64 found ) {
computeAdjustedEndPoints(a, b);
return snapToEdge.refine(adjA, adjB, found);
}
/**
* Used to specify a transform that is applied to pixel coordinates to bring them back into original input
* image coordinates. For example if the input image has lens distortion but the edge were found
* in undistorted coordinates this code needs to know how to go from undistorted back into distorted
* image coordinates in order to read the pixel's value.
*
* @param undistToDist Pixel transformation from undistorted pixels into the actual distorted input image..
*/
public void setTransform( PixelTransform undistToDist ) {
snapToEdge.setTransform(undistToDist);
}
private void computeAdjustedEndPoints(Point2D_F64 a, Point2D_F64 b) {
double slopeX = (b.x - a.x);
double slopeY = (b.y - a.y);
double r = Math.sqrt(slopeX*slopeX + slopeY*slopeY);
// vector of unit length pointing in direction of the slope
double unitX = slopeX/r;
double unitY = slopeY/r;
// offset from corner because the gradient because unstable around there
adjA.x = a.x + unitX*cornerOffset;
adjA.y = a.y + unitY*cornerOffset;
adjB.x = b.x - unitX*cornerOffset;
adjB.y = b.y - unitY*cornerOffset;
}
public SnapToLineEdge getSnapToEdge() {
return snapToEdge;
}
}
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