孤獨的香蕉.png
<h4>一、前言</h6>
寫這篇博客的目的為記錄，并且供大家學習，希望大家多多交流，有不正確的地方請指正，輕噴。！~~
<h4>二、透視校正 簡介 </h6>
透視校正或者稱為透視控制是對照片進行合成或者編輯以得到符合大眾對于透視失真理解的結果的過程。
<h4>三、流程</h6>
首先想要對照片中的物體進行透視校正 所以就先要找到圖片中的物體，一般都是矩形的物體，所以就需要用到OpenCv中找矩形的方法先找到圖片中所有的矩形，然后判斷尋找最大的矩形，然后再對這個矩形進行校正就OK拉。
<h3>上代碼:</h3>
//尋找矩形
- (void)detectEdges{
cv::Mat original = [BLOpenCVHelper cvMatFromUIImage:_myImageView.image];
CGSize targetSize = self.myImageView.contentSize;
//把圖片按比例縮小，因為屏幕顯示的圖片并不是實際大小，所以需要把圖片的大小按比例縮小成當前屏幕的大小，并且映射過去，這樣找矩形的時候返回的4個點坐標才是正確的
cv::resize(original, original, cvSize(targetSize.width, targetSize.height));
std::vector<std::vector<cv::Point>>squares;
std::vector<cv::Point> largest_square;
//尋找矩形
find_squares(original, squares);
//尋找最大的矩形
find_largest_square(squares, largest_square);
if (largest_square.size() == 4) {
// Manually sorting points, needs major improvement. Sorry.
NSMutableArray *points = [NSMutableArray array];
NSMutableDictionary *sortedPoints = [NSMutableDictionary dictionary];
for (int i = 0; i < 4; i++)
{
NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:[NSValue valueWithCGPoint:CGPointMake(largest_square[i].x, largest_square[i].y)], @"point" , [NSNumber numberWithInt:(largest_square[i].x + largest_square[i].y)], @"value", nil];
[points addObject:dict];
}
int min = [[points valueForKeyPath:@"@min.value"] intValue];
int max = [[points valueForKeyPath:@"@max.value"] intValue];
int minIndex = 0;
int maxIndex = 0;
int missingIndexOne = 0;
int missingIndexTwo = 0;
for (int i = 0; i < 4; i++)
{
NSDictionary *dict = [points objectAtIndex:i];
if ([[dict objectForKey:@"value"] intValue] == min)
{
[sortedPoints setObject:[dict objectForKey:@"point"] forKey:@"0"];
minIndex = i;
continue;
}
if ([[dict objectForKey:@"value"] intValue] == max)
{
[sortedPoints setObject:[dict objectForKey:@"point"] forKey:@"2"];
maxIndex = i;
continue;
}
missingIndexOne = i;
}
for (int i = 0; i < 4; i++)
{
if (missingIndexOne != i && minIndex != i && maxIndex != i)
{
missingIndexTwo = i;
}
}
if (largest_square[missingIndexOne].x < largest_square[missingIndexTwo].x)
{
//2nd Point Found
[sortedPoints setObject:[[points objectAtIndex:missingIndexOne] objectForKey:@"point"] forKey:@"3"];
[sortedPoints setObject:[[points objectAtIndex:missingIndexTwo] objectForKey:@"point"] forKey:@"1"];
}
else
{
//4rd Point Found
[sortedPoints setObject:[[points objectAtIndex:missingIndexOne] objectForKey:@"point"] forKey:@"1"];
[sortedPoints setObject:[[points objectAtIndex:missingIndexTwo] objectForKey:@"point"] forKey:@"3"];
}
CGPoint point0 = [(NSValue *)[sortedPoints objectForKey:@"0"] CGPointValue];
CGPoint point1 = [(NSValue *)[sortedPoints objectForKey:@"1"] CGPointValue];
CGPoint point2 = [(NSValue *)[sortedPoints objectForKey:@"2"] CGPointValue];
CGPoint point3 = [(NSValue *)[sortedPoints objectForKey:@"3"] CGPointValue];
[_cropRect topLeftCornerToCGPoint:CGPointMake(point0.x+_myImageView.contentFrame.origin.x, point0.y+_myImageView.contentFrame.origin.y)];
[_cropRect topRightCornerToCGPoint:CGPointMake(point1.x+_myImageView.contentFrame.origin.x, point1.y+_myImageView.contentFrame.origin.y)];
[_cropRect bottomRightCornerToCGPoint:CGPointMake(point2.x+_myImageView.contentFrame.origin.x, point2.y+_myImageView.contentFrame.origin.y)];
[_cropRect bottomLeftCornerToCGPoint:CGPointMake(point3.x+_myImageView.contentFrame.origin.x, point3.y+_myImageView.contentFrame.origin.y)];
}
else{
//沒找到的時候
[_cropRect topLeftCornerToCGPoint:CGPointMake(50, 100)];
[_cropRect topRightCornerToCGPoint:CGPointMake(SCREEN_WIDTH-50, 100)];
[_cropRect bottomRightCornerToCGPoint:CGPointMake(SCREEN_WIDTH-50, SCREEN_HEIGHT-126)];
[_cropRect bottomLeftCornerToCGPoint:CGPointMake(50, SCREEN_HEIGHT-126)];
}
original.release();
}
<h4>接下來是尋找矩形的代碼<h4>
void find_squares(cv::Mat& image, std::vector<std::vector<cv::Point>>&squares) {
// blur will enhance edge detection
cv::Mat blurred(image);
// medianBlur(image, blurred, 9);
GaussianBlur(image, blurred, cvSize(11,11), 0);//change from median blur to gaussian for more accuracy of square detection
cv::Mat gray0(blurred.size(), CV_8U), gray;
std::vector<std::vector<cv::Point> > contours;
// find squares in every color plane of the image
for (int c = 0; c < 3; c++)
{
int ch[] = {c, 0};
mixChannels(&blurred, 1, &gray0, 1, ch, 1);
// try several threshold levels
const int threshold_level = 2;
for (int l = 0; l < threshold_level; l++)
{
// Use Canny instead of zero threshold level!
// Canny helps to catch squares with gradient shading
if (l == 0)
{
Canny(gray0, gray, 10, 20, 3); //
// Canny(gray0, gray, 0, 50, 5);
// Dilate helps to remove potential holes between edge segments
dilate(gray, gray, cv::Mat(), cv::Point(-1,-1));
}
else
{
gray = gray0 >= (l+1) * 255 / threshold_level;
}
// Find contours and store them in a list
findContours(gray, contours, CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE);
// Test contours
std::vector<cv::Point> approx;
for (size_t i = 0; i < contours.size(); i++)
{
// approximate contour with accuracy proportional
// to the contour perimeter
approxPolyDP(cv::Mat(contours[i]), approx, arcLength(cv::Mat(contours[i]), true)*0.02, true);
// Note: absolute value of an area is used because
// area may be positive or negative - in accordance with the
// contour orientation
if (approx.size() == 4 &&
fabs(contourArea(cv::Mat(approx))) > 1000 &&
isContourConvex(cv::Mat(approx)))
{
double maxCosine = 0;
for (int j = 2; j < 5; j++)
{
double cosine = fabs(angle(approx[j%4], approx[j-2], approx[j-1]));
maxCosine = MAX(maxCosine, cosine);
}
if (maxCosine < 0.3)
squares.push_back(approx);
}
}
}
}
}
<h4>最后剪切和校正<h4>
if([_cropRect frameEdited]){
//Thanks To stackOverflow
CGFloat scaleFactor = [_myImageView contentScale];
CGPoint ptBottomLeft = [_cropRect coordinatesForPoint:1 withScaleFactor:scaleFactor];
CGPoint ptBottomRight = [_cropRect coordinatesForPoint:2 withScaleFactor:scaleFactor];
CGPoint ptTopRight = [_cropRect coordinatesForPoint:3 withScaleFactor:scaleFactor];
CGPoint ptTopLeft = [_cropRect coordinatesForPoint:4 withScaleFactor:scaleFactor];
CGFloat w1 = sqrt( pow(ptBottomRight.x - ptBottomLeft.x , 2) + pow(ptBottomRight.x - ptBottomLeft.x, 2));
CGFloat w2 = sqrt( pow(ptTopRight.x - ptTopLeft.x , 2) + pow(ptTopRight.x - ptTopLeft.x, 2));
CGFloat h1 = sqrt( pow(ptTopRight.y - ptBottomRight.y , 2) + pow(ptTopRight.y - ptBottomRight.y, 2));
CGFloat h2 = sqrt( pow(ptTopLeft.y - ptBottomLeft.y , 2) + pow(ptTopLeft.y - ptBottomLeft.y, 2));
CGFloat maxWidth = (w1 < w2) ? w1 : w2;
CGFloat maxHeight = (h1 < h2) ? h1 : h2;
cv::Point2f src[4], dst[4];
src[0].x = ptTopLeft.x;
src[0].y = ptTopLeft.y;
src[1].x = ptTopRight.x;
src[1].y = ptTopRight.y;
src[2].x = ptBottomRight.x;
src[2].y = ptBottomRight.y;
src[3].x = ptBottomLeft.x;
src[3].y = ptBottomLeft.y;
dst[0].x = 0;
dst[0].y = 0;
dst[1].x = maxWidth - 1;
dst[1].y = 0;
dst[2].x = maxWidth - 1;
dst[2].y = maxHeight - 1;
dst[3].x = 0;
dst[3].y = maxHeight - 1;
cv::Mat undistorted = cv::Mat( cvSize(maxWidth,maxHeight), CV_8UC4);
cv::Mat original = [BLOpenCVHelper cvMatFromUIImage:_editorImg];
cv::warpPerspective(original, undistorted, cv::getPerspectiveTransform(src, dst), cvSize(maxWidth, maxHeight));
BLImageViewController *edcVc = [[BLImageViewController alloc] init];
UIImage *img = nil;
//判斷圖片方向
if (_rotateSlider == 0.5f||_rotateSlider == -1.5) {
img = [UIImage imageWithCGImage:[BLOpenCVHelper UIImageFromCVMat:undistorted].CGImage scale:1 orientation:UIImageOrientationRight];
}else if(std::abs(_rotateSlider) == 1.f||_rotateSlider==-3){
img = [UIImage imageWithCGImage:[BLOpenCVHelper UIImageFromCVMat:undistorted].CGImage scale:1 orientation:UIImageOrientationDown];
}else if (_rotateSlider == -0.5 || _rotateSlider == -2.5){
img =[UIImage imageWithCGImage:[BLOpenCVHelper UIImageFromCVMat:undistorted].CGImage scale:1 orientation:UIImageOrientationLeft];
}else{
img = [UIImage imageWithCGImage:[BLOpenCVHelper UIImageFromCVMat:undistorted].CGImage scale:1 orientation:UIImageOrientationUp];
}
//剪切并且跳轉到圖片展示頁面
edcVc.myImage = img;//[MMOpenCVHelper UIImageFromCVMat:undistorted];
[self.navigationController pushViewController:edcVc animated:YES];
original.release();
undistorted.release();
}
接下來是Demo 然后沒了哈哈
