本文档尝试解答如下问题:
- 如何使用OpenCV函数 copyMakeBorder 设置边界(添加额外的边界)。
-
前一节我们学习了图像的卷积操作。一个很自然的问题是如何处理卷积边缘。当卷积点在图像边界时会发生什么，如何处理这个问题？
-
大多数用到卷积操作的OpenCV函数都是将给定图像拷贝到另一个轻微变大的图像中，然后自动填充图像边界(通过下面示例代码中的各种方式)。这样卷积操作就可以在边界像素安全执行了(填充边界在操作完成后会自动删除)。
-
本文档将会探讨填充图像边界的两种方法:
a. BORDER_CONSTANT: 使用常数填充边界 (i.e. 黑色或者 0) b. BORDER_REPLICATE: 复制原图中最临近的行或者列。
#ifdef __cplusplus
#import <opencv2/opencv.hpp>
#import <opencv2/imgcodecs/ios.h>
#import <opencv2/imgproc.hpp>
#import <opencv2/highgui.hpp>
#import <opencv2/core/operations.hpp>
#import <opencv2/core/core_c.h>
using namespace cv;
using namespace std;
#endif
#import "CopyMakeborderViewController.h"
@interface CopyMakeborderViewController ()
@end
@implementation CopyMakeborderViewController
Mat src, dst;
int ctop, cbottom, cleft, cright;
int borderType;
Scalar value;
RNG rng(12345);
- (void)viewDidLoad {
[super viewDidLoad];
UIImage * src1Image = [UIImage imageNamed:@"lena.jpg"];
Mat src = [self cvMatFromUIImage:src1Image];
UIImageView *imageView;
imageView = [self createImageViewInRect:CGRectMake(0, 100, 150, 150)];
[self.view addSubview:imageView];
imageView.image = [self UIImageFromCVMat:src];
ctop = (int) (0.05*src.rows);
cbottom = (int) (0.05*src.rows);
cleft = (int) (0.05*src.cols);
cright = (int) (0.05*src.cols);
dst = src;
[self createButtonFrame:CGRectMake(150, 100, 100, 50) title:@"border" Block:^NSString * _Nonnull(int hitCount) {
if (hitCount%2==0) {
borderType = BORDER_CONSTANT;
}else{
borderType = BORDER_REPLICATE;
}
value = Scalar(rng.uniform(0, 255), rng.uniform(0, 255), rng.uniform(0, 255) );
copyMakeBorder( src, dst, ctop, cbottom, cleft, cright, borderType, value );
UIImageView *imageView;
imageView = [self createImageViewInRect:CGRectMake(0, 250, 150, 150)];
[self.view addSubview:imageView];
imageView.image = [self UIImageFromCVMat:dst];
return nil;
}];
}
#pragma mark - private
//brg
- (cv::Mat)cvMatFromUIImage:(UIImage *)image
{
CGColorSpaceRef colorSpace =CGColorSpaceCreateDeviceRGB();
CGFloat cols = image.size.width;
CGFloat rows = image.size.height;
Mat cvMat(rows, cols, CV_8UC4); // 8 bits per component, 4 channels (color channels + alpha)
CGContextRef contextRef = CGBitmapContextCreate(cvMat.data, // Pointer to data
cols, // Width of bitmap
rows, // Height of bitmap
8, // Bits per component
cvMat.step[0], // Bytes per row
colorSpace, // Colorspace
kCGImageAlphaNoneSkipLast |
kCGBitmapByteOrderDefault); // Bitmap info flags
CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage);
CGContextRelease(contextRef);
Mat dst;
Mat src;
cvtColor(cvMat, dst, COLOR_RGBA2BGRA);
cvtColor(dst, src, COLOR_BGRA2BGR);
return src;
}
-(UIImage *)UIImageFromCVMat:(cv::Mat)cvMat
{
// mat 是brg 而 rgb
Mat src;
NSData *data=nil;
CGBitmapInfo info =kCGImageAlphaNone|kCGBitmapByteOrderDefault;
CGColorSpaceRef colorSpace;
if (cvMat.depth()!=CV_8U) {
Mat result;
cvMat.convertTo(result, CV_8U,255.0);
cvMat = result;
}
if (cvMat.elemSize() == 1) {
colorSpace = CGColorSpaceCreateDeviceGray();
data= [NSData dataWithBytes:cvMat.data length:cvMat.elemSize()*cvMat.total()];
} else if(cvMat.elemSize() == 3){
cvtColor(cvMat, src, COLOR_BGR2RGB);
data= [NSData dataWithBytes:src.data length:src.elemSize()*src.total()];
colorSpace = CGColorSpaceCreateDeviceRGB();
}else if(cvMat.elemSize() == 4){
colorSpace = CGColorSpaceCreateDeviceRGB();
cvtColor(cvMat, src, COLOR_BGRA2RGBA);
data= [NSData dataWithBytes:src.data length:src.elemSize()*src.total()];
info =kCGImageAlphaNoneSkipLast | kCGBitmapByteOrderDefault;
}else{
NSLog(@"[error:] 错误的颜色通道");
return nil;
}
CGDataProviderRef provider = CGDataProviderCreateWithCFData((__bridge CFDataRef)data);
// Creating CGImage from cv::Mat
CGImageRef imageRef = CGImageCreate(cvMat.cols, //width
cvMat.rows, //height
8, //bits per component
8 * cvMat.elemSize(), //bits per pixel
cvMat.step[0], //bytesPerRow
colorSpace, //colorspace
kCGImageAlphaNone|kCGBitmapByteOrderDefault,// bitmap info
provider, //CGDataProviderRef
NULL, //decode
false, //should interpolate
kCGRenderingIntentAbsoluteColorimetric //intent
);
// Getting UIImage from CGImage
UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
CGDataProviderRelease(provider);
CGColorSpaceRelease(colorSpace);
return finalImage;
}
@end
这里其实重点就是学习函数
copyMakeBorder( src, dst, top, bottom, left, right, borderType, value );
接受参数:
- src: 原图像
- dst: 目标图像
- top, bottom, left, right: 各边界的宽度，此处定义为原图像尺寸的5%。
- borderType: 边界类型，此处可以选择常数边界或者复制边界。
- value: 如果 borderType 类型是 BORDER_CONSTANT, 该值用来填充边界像素。
