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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.sfm.d2;
import boofcv.abst.sfm.d2.ImageMotion2D;
import boofcv.alg.distort.DistortImageOps;
import boofcv.alg.distort.ImageDistort;
import boofcv.alg.misc.GImageMiscOps;
import boofcv.struct.distort.PixelTransform;
import boofcv.struct.image.ImageBase;
import georegression.metric.Area2D_F64;
import georegression.struct.InvertibleTransform;
import georegression.struct.homography.Homography2D_F64;
import georegression.struct.point.Point2D_F32;
import georegression.struct.point.Point2D_F64;
import georegression.struct.shapes.RectangleLength2D_I32;
/**
* Stitches together sequences of images using {@link ImageMotion2D}, typically used for image stabilization
* and creating mosaics. Internally any motion model in the Homogeneous family can be used. For convenience,
* those models are converted into a {@link Homography2D_F64} on output.
*
* The size of the stitch region is specified using {@link #configure(int, int, georegression.struct.InvertibleTransform)}
* which must be called before any images are processed. One of the parameters include an initial transform. The
* initial transform can be used to scale/translate/other the input image.
*
* A sudden change or jump in the shape of the view area can be an indication of a bad motion estimate. If a large
* jump larger than the user specified threshold is detected then {@link #process(boofcv.struct.image.ImageBase)}
* will return false.
*
* @author Peter Abeles
*/
public class StitchingFromMotion2D, IT extends InvertibleTransform>
{
// REFERENCE FRAME NOTES:
//
// World references to the stitched image
// Initial is the first video frame in video coordinates
// Current is the current video frame in video coordinates
// estimates image motion
private ImageMotion2D motion;
// renders the distorted image according to results from motion
private ImageDistort distorter;
// converts different types of motion models into other formats
private StitchingTransform converter;
// Transform from first video frame to the initial location in the stitched image
private IT worldToInit;
// size of the stitch image
private int widthStitch, heightStitch;
// Largest allowed fractional change in area
private double maxJumpFraction;
// image corners are used to detect large motions
private Corners corners = new Corners();
// size of view area in previous update
private double previousArea;
// storage for the transform from current frame to the initial frame
private IT worldToCurr;
private PixelTransform tranWorldToCurr;
private PixelTransform tranCurrToWorld;
private Point2D_F32 work = new Point2D_F32();
// storage for the stitched image
private I stitchedImage;
private I workImage;
// first time that it has been called
private boolean first = true;
/**
* Provides internal algorithms and tuning parameters.
*
* @param motion Estimates image motion
* @param distorter Applies found transformation to stitch images
* @param converter Converts internal model into a homogenous transformation
* @param maxJumpFraction If the view area changes by more than this fraction a fault is declared
*/
public StitchingFromMotion2D(ImageMotion2D motion,
ImageDistort distorter,
StitchingTransform converter ,
double maxJumpFraction )
{
this.motion = motion;
this.distorter = distorter;
this.converter = converter;
this.maxJumpFraction = maxJumpFraction;
worldToCurr = (IT)motion.getFirstToCurrent().createInstance();
}
/**
* Specifies size of stitch image and the location of the initial coordinate system.
*
* @param widthStitch Width of the image being stitched into
* @param heightStitch Height of the image being stitched into
* @param worldToInit (Option) Used to change the location of the initial frame in stitched image.
* null means no transform.
*/
public void configure( int widthStitch, int heightStitch , IT worldToInit ) {
this.worldToInit = (IT)worldToCurr.createInstance();
if( worldToInit != null )
this.worldToInit.set(worldToInit);
this.widthStitch = widthStitch;
this.heightStitch = heightStitch;
}
/**
* Estimates the image motion and updates stitched image. If it is unable to estimate the motion then false
* is returned and the stitched image is left unmodified. If false is returned then in most situations it is
* best to call {@link #reset()} and start over.
*
* @param image Next image in the sequence
* @return True if the stitched image is updated and false if it failed and was not
*/
public boolean process( I image ) {
if( stitchedImage == null ) {
stitchedImage = (I)image.createNew(widthStitch, heightStitch);
workImage = (I)image.createNew(widthStitch, heightStitch);
}
if( motion.process(image) ) {
update(image);
// check to see if an unstable and improbably solution was generated
return !checkLargeMotion(image.width, image.height);
} else {
return false;
}
}
/**
* Throws away current results and starts over again
*/
public void reset() {
if( stitchedImage != null )
GImageMiscOps.fill(stitchedImage, 0);
motion.reset();
worldToCurr.reset();
first = true;
}
/**
* Looks for sudden large changes in corner location to detect motion estimation faults.
* @param width image width
* @param height image height
* @return true for fault
*/
private boolean checkLargeMotion( int width , int height ) {
if( first ) {
getImageCorners(width,height,corners);
previousArea = computeArea(corners);
first = false;
} else {
getImageCorners(width,height,corners);
double area = computeArea(corners);
double change = Math.max(area/previousArea,previousArea/area)-1;
if( change > maxJumpFraction ) {
return true;
}
previousArea = area;
}
return false;
}
private double computeArea( Corners c ) {
return Area2D_F64.triangle(c.p0,c.p1,c.p2) +
Area2D_F64.triangle(c.p0,c.p2,c.p3);
}
/**
* Adds the latest image into the stitched image
*
* @param image
*/
private void update(I image) {
computeCurrToInit_PixelTran();
// only process a cropped portion to speed up processing
RectangleLength2D_I32 box = DistortImageOps.boundBox(image.width, image.height,
stitchedImage.width, stitchedImage.height,work, tranCurrToWorld);
int x0 = box.x0;
int y0 = box.y0;
int x1 = box.x0 + box.width;
int y1 = box.y0 + box.height;
distorter.setModel(tranWorldToCurr);
distorter.apply(image, stitchedImage,x0,y0,x1,y1);
}
private void computeCurrToInit_PixelTran() {
IT initToCurr = motion.getFirstToCurrent();
worldToInit.concat(initToCurr, worldToCurr);
tranWorldToCurr = converter.convertPixel(worldToCurr,tranWorldToCurr);
IT currToWorld = (IT) this.worldToCurr.invert(null);
tranCurrToWorld = converter.convertPixel(currToWorld, tranCurrToWorld);
}
/**
* Sets the current image to be the origin of the stitched coordinate system. The background is filled
* with a value of 0.
* Must be called after {@link #process(boofcv.struct.image.ImageBase)}.
*/
public void setOriginToCurrent() {
IT currToWorld = (IT)worldToCurr.invert(null);
IT oldWorldToNewWorld = (IT) worldToInit.concat(currToWorld,null);
PixelTransform newToOld = converter.convertPixel(oldWorldToNewWorld,null);
// fill in the background color
GImageMiscOps.fill(workImage, 0);
// render the transform
distorter.setModel(newToOld);
distorter.apply(stitchedImage, workImage);
// swap the two images
I s = workImage;
workImage = stitchedImage;
stitchedImage = s;
// have motion estimates be relative to this frame
motion.setToFirst();
first = true;
computeCurrToInit_PixelTran();
}
/**
* Resizes the stitch image. If no transform is provided then the old stitch region is simply
* places on top of the new one and copied. Pixels which do not exist in the old image are filled with zero.
*
* @param widthStitch The new width of the stitch image.
* @param heightStitch The new height of the stitch image.
* @param newToOldStitch (Optional) Transform from new stitch image pixels to old stick pixels. Can be null.
*/
public void resizeStitchImage( int widthStitch, int heightStitch , IT newToOldStitch ) {
// copy the old image into the new one
workImage.reshape(widthStitch,heightStitch);
GImageMiscOps.fill(workImage, 0);
if( newToOldStitch != null ) {
PixelTransform newToOld = converter.convertPixel(newToOldStitch,null);
distorter.setModel(newToOld);
distorter.apply(stitchedImage, workImage);
// update the transforms
IT tmp = (IT)worldToCurr.createInstance();
newToOldStitch.concat(worldToInit, tmp);
worldToInit.set(tmp);
computeCurrToInit_PixelTran();
} else {
int overlapWidth = Math.min(widthStitch,stitchedImage.width);
int overlapHeight = Math.min(heightStitch,stitchedImage.height);
GImageMiscOps.copy(0,0,0,0,overlapWidth,overlapHeight,stitchedImage,workImage);
}
stitchedImage.reshape(widthStitch,heightStitch);
I tmp = stitchedImage;
stitchedImage = workImage;
workImage = tmp;
this.widthStitch = widthStitch;
this.heightStitch = heightStitch;
}
/**
* Returns the location of the input image's corners inside the stitch image.
*
* @return image corners
*/
public Corners getImageCorners( int width , int height , Corners corners ) {
if( corners == null )
corners = new Corners();
int w = width;
int h = height;
tranCurrToWorld.compute(0,0,work); corners.p0.set(work.x, work.y);
tranCurrToWorld.compute(w,0,work); corners.p1.set(work.x, work.y);
tranCurrToWorld.compute(w,h,work); corners.p2.set(work.x, work.y);
tranCurrToWorld.compute(0,h,work); corners.p3.set(work.x, work.y);
return corners;
}
/**
* Transform from world coordinate system into the current image frame.
*
* @return Transformation
*/
public Homography2D_F64 getWorldToCurr( Homography2D_F64 storage ) {
return converter.convertH(worldToCurr,storage);
}
public IT getWorldToCurr() {
return worldToCurr;
}
public I getStitchedImage() {
return stitchedImage;
}
public ImageMotion2D getMotion() {
return motion;
}
public static class Corners {
public Point2D_F64 p0 = new Point2D_F64();
public Point2D_F64 p1 = new Point2D_F64();
public Point2D_F64 p2 = new Point2D_F64();
public Point2D_F64 p3 = new Point2D_F64();
}
}