Having trouble creating UIImage from CIImage in iOS5

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];

spybart · Answer 1 · 2011-10-17T01:31:10.700

35

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

edited Oct 17 '11 at 01:31

answered Oct 17 '11 at 01:07

spybart

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Thanks -- this does indeed let me draw the image. However it leaks memory causing the app to crash after running a few seconds. – user491880 Oct 17 '11 at 02:08
Yea, I haven't really looked into it too much yet. I'm sure you have to release the contexts or the CGImageRef at some point. Also I'm sure the method above isn't the practical way of using CIImage views. I plan to watch the "Using Core Image on iOS & Mac OS X" video (which is on the Apple Developer site, WWDC 2011 Session Videos) tomorrow and learn more in-depth, I'll drop a line if I learn anything useful. – spybart Oct 17 '11 at 02:16
I recommend you also watch this video and/or look at the presentation slides as it explains how to use Core Image, and goes into detail about contexts and when to use CPU/GPU and more – spybart Oct 17 '11 at 21:17
I also found this to be useful: OpenGL ES Programming Guide for iOS http://developer.apple.com/library/ios/#documentation/3DDrawing/Conceptual/OpenGLES_ProgrammingGuide/WorkingwithEAGLContexts/WorkingwithEAGLContexts.html – spybart Oct 17 '11 at 21:44
Would you mind explaining why this works vs. imageWithCIImage? I agree with you, I just can't understand why imageWithCIImage alone does not work, as it should according to the docs. – akaru Nov 09 '11 at 06:24
It sounds like imageWithCGImage does not retain the given CGImage. When you call _create_CGImage you get a non-autoreleased object, so it is not freed - This is probably the cause for it working but also leaking... – Oded Ben Dov Dec 02 '11 at 21:22
3

@akaru here's what UIImage reference says about its CGImage property: "If the UIImage object was initialized using a CIImage object, the value of the property is NULL". and it looks like UIImageView tries to access UIImage's CGImage in its implementation. this also looks to be the case for UIImagePNGRepresentation function - it returns nil if UIImage is not CGImage-based. But +[CIContext createCGImage:] just does what it says - creates CGImage, so it works – Russian Jan 07 '12 at 13:25
A good answer by Tulca, @akaru you should select this answer. – C4 - Travis Mar 10 '12 at 06:42
@C4-Travis it's not my question to answer. – akaru Jan 06 '13 at 23:44
@akaru oops! sorry for that. – C4 - Travis Jan 08 '13 at 19:07
@Russian thanks for finding the explanation! No way I would have figured it out on my own. Also, I will point out that we have to use alloc/init instead of the convenience methods for creating the CIImage to get this to work. – windson May 18 '13 at 00:22
@spybart Your code leaks: [context createCGImage...] creates a CGContextRef that must be released (even in ARC). Since you don't assign it to a variable, you cannot release it, and you leak quite a bit of memory here. – xaphod Aug 17 '16 at 15:10

user491880 · Answer 2 · 2011-11-26T01:17:44.810

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!

score 3 · Answer 3 · answered May 10 '12 at 13:12

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

answered May 10 '12 at 13:12

sathiamoorthy

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Did not work for me. I created the CIImage in a different way than shown here. – Automatico Dec 28 '15 at 13:34

score 3 · Answer 4 · answered Mar 18 '15 at 13:56

3

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.

answered Mar 18 '15 at 13:56

JVillella

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brilliant, thanks!!! I wonder why Apple provides [UIImage imageWithCIImage] if it rarely works. Thanks Apple. – Duck Apr 20 '17 at 11:42
1

I ran into some very subtle color distortion and alpha blending issues with this method, fixed by setting color space context = [CIContext contextWithOptions:@{kCIContextWorkingColorSpace : [NSNull null]}]; – user1055568 Oct 08 '17 at 04:19
Thanks @user1055568 that was the critical piece of information we needed – Airsource Ltd Feb 07 '19 at 21:28

Having trouble creating UIImage from CIImage in iOS5

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