OpenCV MatToUIImage causes a memory leak

Question

My project works with openCV for iOS (2.4.9). And I found the MatToUIImage function that will cause a memory leak, and this will only happen in iOS 10.X.

After updating this function (2.4.9) to the latest version (3.2.0), everything worked. The only difference is CGBitmapInfo .

So can someone tell me why?

2.4.9

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

    NSData *data = [NSData dataWithBytes:image.data
                                  length:image.elemSize()*image.total()];

    CGColorSpaceRef colorSpace;

    if (image.elemSize() == 1) {
        colorSpace = CGColorSpaceCreateDeviceGray();
    } else {
        colorSpace = CGColorSpaceCreateDeviceRGB();
    }

    CGDataProviderRef provider =
            CGDataProviderCreateWithCFData((__bridge CFDataRef)data);

    // Creating CGImage from cv::Mat
    CGImageRef imageRef = CGImageCreate(image.cols,
                                        image.rows,
                                        8,
                                        8 * image.elemSize(),
                                        image.step.p[0],
                                        colorSpace,
                                        kCGImageAlphaNone|
                                        kCGBitmapByteOrderDefault,
                                        provider,
                                        NULL,
                                        false,
                                        kCGRenderingIntentDefault
                                        );


    // Getting UIImage from CGImage
    UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpace);

    return finalImage;
}

3.2.0

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

    NSData *data = [NSData dataWithBytes:image.data
                                  length:image.elemSize()*image.total()];

    CGColorSpaceRef colorSpace;

    if (image.elemSize() == 1) {
        colorSpace = CGColorSpaceCreateDeviceGray();
    } else {
        colorSpace = CGColorSpaceCreateDeviceRGB();
    }

    CGDataProviderRef provider =
            CGDataProviderCreateWithCFData((__bridge CFDataRef)data);

    // Preserve alpha transparency, if exists
    bool alpha = image.channels() == 4;
    CGBitmapInfo bitmapInfo = (alpha ? kCGImageAlphaLast : kCGImageAlphaNone) | kCGBitmapByteOrderDefault;

    // Creating CGImage from cv::Mat
    CGImageRef imageRef = CGImageCreate(image.cols,
                                        image.rows,
                                        8,
                                        8 * image.elemSize(),
                                        image.step.p[0],
                                        colorSpace,
                                        bitmapInfo,
                                        provider,
                                        NULL,
                                        false,
                                        kCGRenderingIntentDefault
                                        );


    // Getting UIImage from CGImage
    UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpace);

    return finalImage;
}

Answer 1

(5.06.2017) , CFRelease , , ! , , - NSData () .

, , , ARC , :

- (void)runInBackgroundWithImageBuffer:(CVImageBufferRef)imageBuffer
                              callback:(void (^)())callback {
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(queue, ^{
        [self processImageBuffer:imageBuffer];
        if (callback != nil) {
            callback();
        }
    });
}

- (void)previewOpenCVImage:(cv::Mat *)image {
    UIImage *preview = MatToUIImage(*image);

    dispatch_async(dispatch_get_main_queue(), ^{
        // _imagePreview has (UIImageView *) type
        [_imagePreview setImage:preview];
    });
}

iPhone Simulator. , MatToUIImage . .

- , .

, :

• CFRelease((CFTypeRef)data)

• , CFRelease(image.CGImage) , , CFRelease((CFTypeRef)image)

, . , , .