问题描述
我必须构建一个程序，以倾斜的形式（已扫描的图像）进行图像处理。第一步是摆脱扭曲。我成功获取了图像的轮廓，并且尝试进行本帖子Remove top section of image above border line to detect text document中介绍的four_point_transform。但是，由于以下原因，我的代码失败了：
java.lang.RuntimeException: OpenCV(4.4.0) C:\projects\javacpp-presets\opencv\cppbuild\windows-x86_64\opencv-4.4.0\modules\imgproc\src\imgwarp.cpp:3391: error: (-215:Assertion Failed) src.checkVector(2,CV_32F) == 4 && dst.checkVector(2,CV_32F) == 4 in function 'cv::getPerspectiveTransform
protected static void fixSkeweness(Mat mat){
Mat mask = new Mat();
Mat gray = new Mat();
Mat denoised = new Mat();
Mat bin = new Mat();
Mat hierarchy = new Mat();
MatVector contours = new MatVector();
cvtColor(mat,gray,COLOR_BGR2GRAY);
//normalize
GaussianBlur(gray,denoised,new Size(5,5),0);
threshold(denoised,mask,255,THRESH_BINARY_INV | THRESH_OTSU);
normalize(gray,norM_MINMAX,-1,mask);
// Convert image to binary
threshold(gray,bin,150,THRESH_BINARY);
// Find contours
findContours(bin,contours,hierarchy,RETR_TREE,CHAIN_APPROX_NONE);
long contourCount = contours.size();
System.out.println("Countour count " + contourCount);
double maxArea = 0;
int maxAreaId = 0;
for (int i = 0; i < contourCount; ++i) {
// Calculate the area of each contour
Mat contour = contours.get(i);
double area = contourArea(contour);
if(area > maxArea){
maxAreaId = i;
maxArea = area;
}
}
Double peri = arcLength(contours.get(maxAreaId),true);
Mat newcontour = new Mat();
approxpolyDP(contours.get(maxAreaId),newcontour,0.02 * peri,true);
Mat result = new Mat();
getPerspectiveTransform(newcontour.reshape(4,2),result);
imwrite("src/test/resources/isDataPage/fourPointTransform.jpg",result);
}
失败的代码行是：
getPerspectiveTransform(newcontour.reshape(4,result);
请给我一些帮助，以使其正常工作吗？
示例图片：
根据建议答案使用的工作代码
protected static Mat findBiggestContour(Mat mat){
Mat mask = new Mat();
Mat gray = new Mat();
Mat denoised = new Mat();
Mat bin = new Mat();
Mat hierarchy = new Mat();
MatVector contours = new MatVector();
//Pre-process image
cvtColor(mat,COLOR_BGR2GRAY);
threshold(gray,THRESH_BINARY_INV + THRESH_OTSU);
findContours(bin,CHAIN_APPROX_SIMPLE);
double maxArea = 0;
int maxAreaId = 0;
for (int i = 0; i < contours.size(); ++i) {
// Calculate the area of each contour
Mat contour = contours.get(i);
double area = contourArea(contour);
if(area > 5000 && i!=0){
maxAreaId = i;
maxArea = area;
}
}
//Get Min Area Rect and inverse it
RotatedRect rect = minAreaRect(contours.get(maxAreaId));
float newAngle = rect.angle();
if (rect.angle() < 45){
newAngle = newAngle + 90;
}
RotatedRect angle =rect.angle( newAngle);
int h = mat.size().height();
int w = mat.size().width();
int centerW = w/2;
int centerH = h/2;
//find rotation matrix and apply it woohoo
Point2f center = new Point2f(centerW,centerH);
Mat m = getRotationMatrix2D(center,angle.angle(),1.0);
Mat rotated = new Mat();
warpAffine(mat,rotated,m,new Size(w,h),INTER_CUBIC,BORDER_REPLICATE,new Scalar(10,10));
imwrite("src/test/resources/tmp2/rotrated.png",rotated);
return rotated;
}
解决方法
getPerspectiveTransform()正在以其他方式工作（请参阅我的评论）。但是，我发现minAreaRect()是更合适的方法。我没有准备好的Java环境，所以这里是python代码。希望您在转换时不会遇到困难。
img = cv2.imread('images/form.png')
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
# some preprocessing as you did
# your src image is pretty clean though,and if they all are like that,# I wouldn't use blur as it makes form borders less obvious
# gray = cv2.blur(gray,(5,5))
thresh = cv2.threshold(gray,255,cv2.THRESH_BINARY_INV + cv2.THRESH_OTSU)[1]
# find the largest contour assuming it will be some nice rectangle
ctrs,hier = cv2.findContours(thresh,cv2.RETR_LIST,cv2.CHAIN_APPROX_SIMPLE)
largest_ctr_idx = max(range(len(ctrs)),key=lambda i: cv2.contourArea(ctrs[i]))
# get the contour's rotation angle
angle = cv2.minAreaRect(ctrs[largest_ctr_idx])[-1]
if angle < -45:
angle += 90
# find rotation matrix and apply it woohoo
h,w = img.shape[:2]
center = (w // 2,h // 2)
m = cv2.getRotationMatrix2D(center,angle,1.0)
rotated = cv2.warpAffine(img,m,(w,h),flags=cv2.INTER_CUBIC,borderMode=cv2.BORDER_REPLICATE)
发现轮廓：
歪斜的图像：
