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将CVImageBufferRef转换为PNG

qtkit cgimage png macos cocoa

nacho4d · 技术社区 · 14 年前

我想使用将所有帧写入磁盘QTKit.框架用于摄像头输入。但是我得到的所有图像都是半透明的,没有一些颜色,可能是颜色空间的问题?;( 它们在预览视图中看起来不错,但是当我写它们的时候“有些事情”发生了。

-(void)savePNGImage:(CGImageRef)imageRef path:(NSString *)path {
    NSURL *outURL = [[NSURL alloc] initFileURLWithPath:path]; 
    CGImageDestinationRef dr = CGImageDestinationCreateWithURL ((CFURLRef)outURL, (CFStringRef)@"public.png" , 1, NULL);
    CGImageDestinationAddImage(dr, imageRef, NULL);
    CGImageDestinationFinalize(dr);
    [outURL release];
}
-(void)saveJPEGImage:(CGImageRef)imageRef path:(NSString *)path {
    CFMutableDictionaryRef mSaveMetaAndOpts = CFDictionaryCreateMutable(nil, 0,
                                                                    &kCFTypeDictionaryKeyCallBacks,  &kCFTypeDictionaryValueCallBacks);
    CFDictionarySetValue(mSaveMetaAndOpts, kCGImageDestinationLossyCompressionQuality, 
                         [NSNumber numberWithFloat:1.0]);   // set the compression quality here
    NSURL *outURL = [[NSURL alloc] initFileURLWithPath:path];
    CGImageDestinationRef dr = CGImageDestinationCreateWithURL ((CFURLRef)outURL, (CFStringRef)@"public.jpeg" , 1, NULL);
    CGImageDestinationAddImage(dr, imageRef, mSaveMetaAndOpts);
    CGImageDestinationFinalize(dr);
    [outURL release];
}


- (void)captureOutput:(QTCaptureOutput *)captureOutput 
  didOutputVideoFrame:(CVImageBufferRef)videoFrame 
     withSampleBuffer:(QTSampleBuffer *)sampleBuffer 
       fromConnection:(QTCaptureConnection *)connection{

    CVPixelBufferLockBaseAddress(videoFrame,0); 
    uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(videoFrame); 
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(videoFrame); 
    size_t width = CVPixelBufferGetWidth(videoFrame); 
    size_t height = CVPixelBufferGetHeight(videoFrame); 
    CVPixelBufferUnlockBaseAddress(videoFrame,0);

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 
    CGContextRef newContext = CGBitmapContextCreate(baseAddress, 
                                                        width, height, 8, 
                                                        bytesPerRow, 
                                                        colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst); 
        CGImageRef frame = CGBitmapContextCreateImage(newContext); 

    CGContextRelease(newContext); 
    CGColorSpaceRelease(colorSpace);

    [self savePNGImage:frame path:[NSString stringWithFormat:@"/Users/nacho4d/Desktop/framesCam/frame%003d.png", frameNum++]];
[self saveJPEGImage:frame path:[NSString stringWithFormat:@"/Users/nacho4d/Desktop/framesCam/frame%003d.jpeg", frameNum++]];

    CGImageRelease(frame);
}

捕获器属性只是帧大小和像素格式,如下所示: [NSNumber numberWithUnsignedInt:kCVPixelFormatType_32ARGB], (id)kCVPixelBufferPixelFormatTypeKey

我也尝试过JPEG,我得到了同样的图像,像是图像中缺少一些通道,所有写入的帧都有白色背景。(因为JPEG不允许透明??)

alt text (我不显示PNG,因为它是透明的,很难在浏览器中看到)

提前谢谢。

3 回复 | 直到 13 年前

jakeva 13 年前

我不知道你的问题是什么,但下面是我如何保存图像到磁盘。只需传入从委托方法获得的CVImageBufferRef,当然还有您自己的URL,它应该可以正常工作。至少对我来说是这样。祝你好运!

-(void)saveImage:(CVImageBufferRef)image toURL:(NSURL*)url{

    NSCIImageRep *imageRep = [NSCIImageRep imageRepWithCIImage:[CIImage imageWithCVImageBuffer:image]];

    NSImage *_image = [[NSImage alloc] initWithSize:[imageRep size]];
    [_image addRepresentation:imageRep];

    NSData *bitmapData = [_image TIFFRep    resentation];
    NSBitmapImageRep *bitmapRep = [NSBitmapImageRep imageRepWithData:bitmapData];
    NSData *imageData = [bitmapRep representationUsingType:NSJPEGFileType properties:nil];

    [_image release];
    _image = [[NSImage alloc] initWithData:imageData];

    NSBitmapImageRep *imgRep = [[_image representations] objectAtIndex: 0];
    NSData *data = [imgRep representationUsingType: NSPNGFileType properties: nil];
    [data writeToFile: [self getSaveString] atomically: NO];

    [_image release];
}

jjwchoy 13 年前

CVPixelBufferUnlockBaseAddress(videoFrame,0);

到最后

Dave Branton 10 年前

我做了一些类似的事情,看到了同样的问题。我稍微修改了你的代码 kCGImageAlphaPremultipliedFirst kCGImageAlphaNoneSkipFirst . 大概是因为帧不包含alpha,即使它是每像素32位,这就解决了我的问题。