29

我将 OpenCV 框架与 XCode 一起使用，并且想从 cvMat 或 IplImage 转换为 UIImage，该怎么做？谢谢。

4

8 回答 8

45

注意：大多数实现不能正确处理 alpha 通道或从 OpenCV 的 BGR 像素格式转换为 iOS 的 RGB。

这将正确转换cv::Mat为UIImage：

+(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; 
}

并转换UIImage为cv::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;
}
于 2012-04-20T22:55:08.167 回答
30

从 opencv 2.4.6 开始，此功能已包含在内。只包括

opencv2/highgui/ios.h

在 OpenCV 3 中，此包含已更改为：

opencv2/imgcodecs/ios.h

您可以使用以下功能：

UIImage* MatToUIImage(const cv::Mat& image);
void UIImageToMat(const UIImage* image, cv::Mat& m, bool alphaExist = false);
于 2015-02-24T13:56:57.883 回答
5
于 2016-03-14T22:15:48.083 回答
4

You should consider using native OpenCV functions to convert forth and back :

#import <opencv2/imgcodecs/ios.h>
...
UIImage* MatToUIImage(const cv::Mat& image);
void UIImageToMat(const UIImage* image,
                         cv::Mat& m, bool alphaExist = false);
于 2017-03-08T09:57:49.860 回答
2

Here I am mentioning all the needed conversion methods together.

Converting UIImage color to UIImage gray, without using opencv and only using iOS library functions: 

- (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;
}

Converting color UIImage to color cvMat. Please note that, you will find this piece of code in several links but there is a small modification here. Notice the portion "swap channels". This part is for keeping the color undisturbed otherwise the color channel got modified.

Also notice the following lines. These lines will help to keep the orientation of the image undisturbed.

    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;
}

Converting UIImage to cvMat gray. Notice the line

cv::Mat cvMat(rows, cols, CV_8UC4, Scalar(1,2,3,4)); // 8 bits per component, 4 channels

instead of

cv::Mat cvMat(rows, cols, CV_8UC1); // 8 bits per component, 1 channels

This line is needed otherwise the code will throw error

- (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;
}

Now finally, converting cvMat (color,binary, gray) to UIImage (color, binary, gray). Notice the line :

UIImage *finalImage = [UIImage imageWithCGImage:imageRef scale:1 orientation:self.originalImage.imageOrientation];

This line will help to keep the original orientation of the image

ENJOY !! 

-(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;
}
于 2016-10-17T13:12:14.777 回答
1

You should consider using native OpenCV functions to convert forth and back :

#import <opencv2/imgcodecs/ios.h>
...
UIImage* MatToUIImage(const cv::Mat& image);
void UIImageToMat(const UIImage* image,
                         cv::Mat& m, bool alphaExist = false);

Note: if your UIImage comes from the camera, you should 'normalize' it ( iOS UIImagePickerController result image orientation after upload) before converting to cv::Mat since OpenCV does not take into account Exif data. If you don't do that the result should be misoriented.

于 2017-03-08T10:04:05.247 回答
0

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
于 2015-01-05T16:47:38.090 回答
0

What I have experienced with converting between UIImage and cvMat is following:

When I used the method:

UIImage* MatToUIImage(const cv::Mat& image);

for converting cv::Mat to UIImage and the method:

void UIImageToMat(const UIImage* image, cv::Mat& m);

for converting UIImage to cv::Mat these methods didn't work correctly using the Simulator. After I deployed my app on a real device, there weren't any problems.

Best regards, Nazar

于 2016-05-07T21:48:46.160 回答