在iOS5中从CIImage创建UIImage时遇到问题

Question

I'm using the AVFoundation framework. In my sample buffer delegate I have the following code:

-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{
     CVPixelBufferRef pb = CMSampleBufferGetImageBuffer(sampleBuffer);
     CIImage *ciImage = [CIImage imageWithCVPixelBuffer:pb];
     self.imageView.image = [UIImage imageWithCIImage:ciImage];
}

I am able to use the CIImage to run the face detector etc. but it does not show up in the UIImageView ... the imageView remains white. Any ideas as to the problem? I am using the following to setup my session:

    self.session = [[AVCaptureSession alloc] init];
self.session.sessionPreset = AVCaptureSessionPreset640x480;
self.videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
self.videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:nil]; 
self.frameOutput = [[AVCaptureVideoDataOutput alloc] init];
self.frameOutput.videoSettings = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey];

Answer 1

This might help. I was having the same issue (image not being drawn to screen) with this code:

CIImage *image = [[CIImage alloc] initWithImage:[UIImage imageNamed:@"mushroom.jpg"]];

theImageView.image = [UIImage imageWithCIImage:image];

However, after changing the code to this, it now works correctly:

CIImage *image = [[CIImage alloc] initWithImage:[UIImage imageNamed:@"mushroom.jpg"]];

CIContext *context = [CIContext contextWithOptions:nil];

theImageView.image = [UIImage imageWithCGImage:[context createCGImage:image fromRect:image.extent]];

To read more about CIContext take a look here: http://developer.apple.com/library/ios/#DOCUMENTATION/GraphicsImaging/Reference/QuartzCoreFramework/Classes/CIContext_Class/Reference/Reference.html#//apple_ref/occ/cl/CIContext

Answer 2

Here is one way that I got it to work:

CIContext *context = [CIContext contextWithOptions:nil];
CGImageRef ref = [context createCGImage:result fromRect:ciImage.extent];
self.imgView.image = [UIImage imageWithCGImage:ref scale:1.0 orientation:UIImageOrientationRight];
CGImageRelease(ref);

Note: Creating the context multiple times is really bad and actually causes a memory leak. You should just create the context once as a property in your class instance and reuse it!

Answer 3

CIImage *ciImage = [UIImage imageNamed:@"imageName.png"].CIImage;
UIImage *uiImage = [[UIImage alloc] initWithCIImage:ciImage];

Answer 4

Here is a complete code sample that I've used in my projects.

- (UIImage *)makeUIImageFromCIImage:(CIImage *)ciImage {
    CIContext *context = [CIContext contextWithOptions:nil];
    CGImageRef cgImage = [context createCGImage:ciImage fromRect:[ciImage extent]];

    UIImage* uiImage = [UIImage imageWithCGImage:cgImage];
    CGImageRelease(cgImage);

    return uiImage;
}

CIImage is basically a recipe for an image. You will run into problems if you try to directly convert from CIImage to UIImage . For example, calling

NSData * UIImageJPEGRepresentation (
   UIImage *image,
   CGFloat compressionQuality
);

will return nil .