IplImageとUIImageの相互変換

既に色々な方が書いており色々なユーティリティとなっているが、私は取りあえずObjective-Cのクラスユーティリティとして使っている。(そのうち手を入れる予定だ)

• • OpenCVUtil

+ (IplImage*)IplImageFromUIImage:(UIImage*)image
{
    CGImageRef imageRef = image.CGImage;
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    IplImage *iplimage = cvCreateImage(cvSize(image.size.width,image.size.height), IPL_DEPTH_8U, 4 );
    
    CGContextRef contextRef = CGBitmapContextCreate(
                                iplimage->imageData,
                                iplimage->width,
                                iplimage->height,
                                iplimage->depth,
                                iplimage->widthStep,
                                colorSpace,
                                kCGImageAlphaPremultipliedLast|kCGBitmapByteOrderDefault);
    CGContextDrawImage(contextRef,
                       CGRectMake(0, 0, image.size.width, image.size.height),
                       imageRef);
    
    CGContextRelease(contextRef);
    CGColorSpaceRelease(colorSpace);
    
    IplImage *ret = cvCreateImage(cvGetSize(iplimage), IPL_DEPTH_8U, 3);
    cvCvtColor(iplimage, ret, CV_RGBA2BGR);
    cvReleaseImage(&iplimage);
    
    return ret;
}
+ (UIImage*)UIImageFromIplImage:(IplImage*)image
{
    CGColorSpaceRef colorSpace;
    if (image->nChannels == 1)
    {
        colorSpace = CGColorSpaceCreateDeviceGray();
    } else {
        colorSpace = CGColorSpaceCreateDeviceRGB();
        //BGRになっているのでRGBに変換
        cvCvtColor(image, image, CV_BGR2RGB);
    }
    NSData *data = [NSData dataWithBytes:image->imageData length:image->imageSize];
    CGDataProviderRef provider = CGDataProviderCreateWithCFData((__bridge CFDataRef)data);
    CGImageRef imageRef = CGImageCreate(image->width,
                                        image->height,
                                        image->depth,
                                        image->depth * image->nChannels,
                                        image->widthStep,
                                        colorSpace,
                                        kCGImageAlphaNone|kCGBitmapByteOrderDefault,
                                        provider,
                                        NULL,
                                        false,
                                        kCGRenderingIntentDefault
                                        );
    UIImage *ret = [UIImage imageWithCGImage:imageRef];
    
    CGImageRelease(imageRef);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpace);
    
    return ret;
}

cvCvtColorは重要だ。CGImageの色空間は"RGB"でありIplImageの"BGR"とは違うため、この色の変換を忘れるとおかしなことになってしまう。(赤と青が反転する)

使い方は以下のようになるだろう。

UIImage* src = [UIImage imageNamed:@"icebraker.png"];
IplImage* img = [OpenCVUtil IplImageFromUIImage:src];
/** OpenCVによる画像処理　**/
imgProcessed.image = [OpenCVUtil UIImageFromIplImage:img];