我正在将 OpenCV 框架与 Xcode 结合使用，并希望从
cv::MatIplImageUIImage注意：大多数实现无法正确处理 Alpha 通道或从 OpenCV 的 BGR 像素格式转换为 iOS 的 RGB。
这将正确地从
cv::MatUIImage+(UIImage *)UIImageFromCVMat:(cv::Mat)cvMat {
NSData *data = [NSData dataWithBytes:cvMat.data length:image.step.p[0]*image.rows];
CGColorSpaceRef colorSpace;
CGBitmapInfo bitmapInfo;
if (cvMat.elemSize() == 1) {
colorSpace = CGColorSpaceCreateDeviceGray();
bitmapInfo = kCGImageAlphaNone | kCGBitmapByteOrderDefault;
} else {
colorSpace = CGColorSpaceCreateDeviceRGB();
bitmapInfo = kCGBitmapByteOrder32Little | (
cvMat.elemSize() == 3? kCGImageAlphaNone : kCGImageAlphaNoneSkipFirst
);
}
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
bitmapInfo, // bitmap info
provider, //CGDataProviderRef
NULL, //decode
false, //should interpolate
kCGRenderingIntentDefault //intent
);
// Getting UIImage from CGImage
UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
CGDataProviderRelease(provider);
CGColorSpaceRelease(colorSpace);
return finalImage;
}
并将
UIImagecv::Mat+ (cv::Mat)cvMatWithImage:(UIImage *)image
{
CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
size_t numberOfComponents = CGColorSpaceGetNumberOfComponents(colorSpace);
CGFloat cols = image.size.width;
CGFloat rows = image.size.height;
cv::Mat cvMat(rows, cols, CV_8UC4); // 8 bits per component, 4 channels
CGBitmapInfo bitmapInfo = kCGImageAlphaNoneSkipLast | kCGBitmapByteOrderDefault;
// check whether the UIImage is greyscale already
if (numberOfComponents == 1){
cvMat = cv::Mat(rows, cols, CV_8UC1); // 8 bits per component, 1 channels
bitmapInfo = kCGImageAlphaNone | kCGBitmapByteOrderDefault;
}
CGContextRef contextRef = CGBitmapContextCreate(cvMat.data, // Pointer to backing data
cols, // Width of bitmap
rows, // Height of bitmap
8, // Bits per component
cvMat.step[0], // Bytes per row
colorSpace, // Colorspace
bitmapInfo); // Bitmap info flags
CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage);
CGContextRelease(contextRef);
return cvMat;
}
从 opencv 2.4.6 开始，已经包含此功能。 只需包含
opencv2/highgui/ios.h
在 OpenCV 3 中，此包含已更改为：
opencv2/imgcodecs/ios.h
您可以使用这些功能：
UIImage* MatToUIImage(const cv::Mat& image);
void UIImageToMat(const UIImage* image, cv::Mat& m, bool alphaExist = false);
这是将 cv::Mat 转换为
UIImage正确方法。
我见过的所有其他实现（包括 OpenCV 的文档）都是不正确：它们没有正确地从 OpenCV 的 BGR 转换为 iOS 的 RGB，并且它们不考虑 alpha 通道（如果存在）。请参阅上面的评论
bitmapInfo = …+(UIImage *)UIImageFromCVMat:(cv::Mat)cvMat {
NSData *data = [NSData dataWithBytes:cvMat.data length:cvMat.elemSize()*cvMat.total()];
CGColorSpaceRef colorSpace;
CGBitmapInfo bitmapInfo;
if (cvMat.elemSize() == 1) {
colorSpace = CGColorSpaceCreateDeviceGray();
bitmapInfo = kCGImageAlphaNone | kCGBitmapByteOrderDefault;
} else {
colorSpace = CGColorSpaceCreateDeviceRGB();
// OpenCV defaults to either BGR or ABGR. In CoreGraphics land,
// this means using the "32Little" byte order, and potentially
// skipping the first pixel. These may need to be adjusted if the
// input matrix uses a different pixel format.
bitmapInfo = kCGBitmapByteOrder32Little | (
cvMat.elemSize() == 3? kCGImageAlphaNone : kCGImageAlphaNoneSkipFirst
);
}
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
bitmapInfo, // bitmap info
provider, //CGDataProviderRef
NULL, //decode
false, //should interpolate
kCGRenderingIntentDefault //intent
);
// Getting UIImage from CGImage
UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
CGDataProviderRelease(provider);
CGColorSpaceRelease(colorSpace);
return finalImage;
}
您应该考虑使用本机 OpenCV 函数来进行来回转换：
#import <opencv2/imgcodecs/ios.h>
...
UIImage* MatToUIImage(const cv::Mat& image);
void UIImageToMat(const UIImage* image,
cv::Mat& m, bool alphaExist = false);
这里我把所有需要的转换方法都一并提到。
将UIImage颜色转换为UIImage灰色，不使用opencv，仅使用iOS库函数：
- (UIImage *)convertImageToGrayScale:(UIImage *)image
{
// Create image rectangle with current image width/height
CGRect imageRect = CGRectMake(0, 0, image.size.width, image.size.height);
// Grayscale color space
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
// Create bitmap content with current image size and grayscale colorspace
CGContextRef context = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, 0, colorSpace, kCGImageAlphaNone);
// Draw image into current context, with specified rectangle
// using previously defined context (with grayscale colorspace)
CGContextDrawImage(context, imageRect, [image CGImage]);
/* changes start here */
// Create bitmap image info from pixel data in current context
CGImageRef grayImage = CGBitmapContextCreateImage(context);
// release the colorspace and graphics context
CGColorSpaceRelease(colorSpace);
CGContextRelease(context);
// make a new alpha-only graphics context
context = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, 0, nil, kCGImageAlphaOnly);
// draw image into context with no colorspace
CGContextDrawImage(context, imageRect, [image CGImage]);
// create alpha bitmap mask from current context
CGImageRef mask = CGBitmapContextCreateImage(context);
// release graphics context
CGContextRelease(context);
// make UIImage from grayscale image with alpha mask
UIImage *grayScaleImage = [UIImage imageWithCGImage:CGImageCreateWithMask(grayImage, mask) scale:image.scale orientation:image.imageOrientation];
// release the CG images
CGImageRelease(grayImage);
CGImageRelease(mask);
// return the new grayscale image
return grayScaleImage;
}
将彩色 UIImage 转换为彩色 cvMat。请注意，您可以在多个链接中找到这段代码，但这里有一个小的修改。注意“交换频道”部分。这部分是为了保持颜色不受干扰，否则颜色通道会被修改。
另请注意以下几行。这些线将有助于保持图像的方向不受干扰。
if (image.imageOrientation == UIImageOrientationLeft || image.imageOrientation == UIImageOrientationRight) { cols = image.size.height; rows = image.size.width; }
- (cv::Mat)cvMatFromUIImage:(UIImage *)image
{
CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
CGFloat cols = image.size.width;
CGFloat rows = image.size.height;
if (image.imageOrientation == UIImageOrientationLeft
|| image.imageOrientation == UIImageOrientationRight) {
cols = image.size.height;
rows = image.size.width;
}
cv::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);
CGColorSpaceRelease(colorSpace);
//--swap channels -- //
std::vector<Mat> ch;
cv::split(cvMat,ch);
std::swap(ch[0],ch[2]);
cv::merge(ch,cvMat);
return cvMat;
}
将 UIImage 转换为 cvMat 灰色。注意这条线
cv::Mat cvMat(行, 列, CV_8UC4, 标量(1,2,3,4)); // 每 8 位 组件，4 通道
而不是
cv::Mat cvMat(行、列、CV_8UC1); // 每个组件 8 位，1 频道
此行是必需的，否则代码将抛出错误
- (cv::Mat)cvMatGrayFromUIImage:(UIImage *)image
{
CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
CGFloat cols = image.size.width;
CGFloat rows = image.size.height;
// cv::Mat cvMat(rows, cols, CV_8UC1); // 8 bits per component, 1 channels
cv::Mat cvMat(rows, cols, CV_8UC4, Scalar(1,2,3,4)); // 8 bits per component, 4 channels
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);
CGColorSpaceRelease(colorSpace);
return cvMat;
}
现在最后，将 cvMat（颜色，二进制，灰色）转换为 UIImage（颜色，二进制，灰色）。注意这一行：
UIImage *finalImage = [UIImage imageWithCGImage:imageRef scale:1 orientation:self.originalImage.imageOrientation];
这条线将有助于保持图像的原始方向
享受！
-(UIImage *)UIImageFromCVMat:(cv::Mat)cvMat {
NSData *data = [NSData dataWithBytes:cvMat.data length:cvMat.elemSize()*cvMat.total()];
CGColorSpaceRef colorSpace;
CGBitmapInfo bitmapInfo;
if (cvMat.elemSize() == 1) {
colorSpace = CGColorSpaceCreateDeviceGray();
bitmapInfo = kCGImageAlphaNone | kCGBitmapByteOrderDefault;
} else {
colorSpace = CGColorSpaceCreateDeviceRGB();
bitmapInfo = kCGBitmapByteOrder32Little | (
cvMat.elemSize() == 3? kCGImageAlphaNone : kCGImageAlphaNoneSkipFirst
);
}
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
bitmapInfo, // bitmap info
provider, //CGDataProviderRef
NULL, //decode
false, //should interpolate
kCGRenderingIntentDefault //intent
);
// Getting UIImage from CGImage
UIImage *finalImage = [UIImage imageWithCGImage:imageRef scale:1 orientation:self.originalImage.imageOrientation];
CGImageRelease(imageRef);
CGDataProviderRelease(provider);
CGColorSpaceRelease(colorSpace);
return finalImage;
}
您应该考虑使用本机 OpenCV 函数来进行来回转换：
#import <opencv2/imgcodecs/ios.h>
...
UIImage* MatToUIImage(const cv::Mat& image);
void UIImageToMat(const UIImage* image,
cv::Mat& m, bool alphaExist = false);
注意：如果你的 UIImage 来自相机，你应该“标准化”它（ iOS UIImagePickerController 结果上传后图像方向）在转换为
cv::Mat作为一个类别：
#import <UIKit/UIKit.h>
#import <opencv2/core/core.hpp>
using namespace cv;
@interface UIImage (OCV)
-(id)initWithOImage:(cv::Mat)oImage;
-(cv::Mat)oImage;
@end
和
#import "UIImage+OCV.h"
@implementation UIImage (OCV)
-(id)initWithOImage:(cv::Mat)oImage
{
NSData *data = [NSData dataWithBytes:oImage.data length:oImage.elemSize() * oImage.total()];
CGColorSpaceRef colorSpace;
if (oImage.elemSize() == 1) {
colorSpace = CGColorSpaceCreateDeviceGray();
} else {
colorSpace = CGColorSpaceCreateDeviceRGB();
}
CGDataProviderRef provider = CGDataProviderCreateWithCFData((__bridge CFDataRef)data);
CGImageRef imageRef = CGImageCreate(oImage.cols, // Width
oImage.rows, // Height
8, // Bits per component
8 * oImage.elemSize(), // Bits per pixel
oImage.step[0], // Bytes per row
colorSpace, // Colorspace
kCGImageAlphaNone | kCGBitmapByteOrderDefault, // Bitmap info flags
provider, // CGDataProviderRef
NULL, // Decode
false, // Should interpolate
kCGRenderingIntentDefault); // Intent
self = [self initWithCGImage:imageRef];
CGImageRelease(imageRef);
CGDataProviderRelease(provider);
CGColorSpaceRelease(colorSpace);
return self;
}
-(cv::Mat)oImage
{
CGColorSpaceRef colorSpace = CGImageGetColorSpace(self.CGImage);
CGFloat cols = self.size.width;
CGFloat rows = self.size.height;
cv::Mat cvMat(rows, cols, CV_8UC4); // 8 bits per component, 4 channels
CGContextRef contextRef = CGBitmapContextCreate(cvMat.data, // Pointer to backing 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), self.CGImage);
CGContextRelease(contextRef);
return cvMat;
}
@end
我在 UIImage 和 cvMat 之间转换的经历如下：
我使用方法时：
UIImage* MatToUIImage(const cv::Mat& image);
用于将 cv::Mat 转换为 UIImage 以及方法：
void UIImageToMat(const UIImage* image, cv::Mat& m);
将 UIImage 转换为 cv::Mat 这些方法在使用模拟器时无法正常工作。 当我在真实设备上部署我的应用程序后，没有任何问题。
最诚挚的问候， 纳扎尔