Memory leak in CoreImage/CoreVideo - ios

Question

I'm build an iOS app that does some basic detection.
I get the raw frames from AVCaptureVideoDataOutput, convert the CMSampleBufferRef to a UIImage, resize the UIImage, then convert it to a CVPixelBufferRef.
As far as I can detect with Instruments the leak is the last part where I convert the CGImage to a CVPixelBufferRef.
Here's the code I use:
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
videof = [[ASMotionDetect alloc] initWithSampleImage:[self resizeSampleBuffer:sampleBuffer]];
// ASMotionDetect is my class for detection and I use videof to calculate the movement
}
-(UIImage*)resizeSampleBuffer:(CMSampleBufferRef) sampleBuffer {
UIImage *img;
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
CVPixelBufferLockBaseAddress(imageBuffer,0); // Lock the image buffer
uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 0); // Get information of the image
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
size_t width = CVPixelBufferGetWidth(imageBuffer);
size_t height = CVPixelBufferGetHeight(imageBuffer);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
CGImageRef newImage = CGBitmapContextCreateImage(newContext);
CGContextRelease(newContext);
CGColorSpaceRelease(colorSpace);
CVPixelBufferUnlockBaseAddress(imageBuffer,0);
/* CVBufferRelease(imageBuffer); */ // do not call this!
img = [UIImage imageWithCGImage:newImage];
CGImageRelease(newImage);
newContext = nil;
img = [self resizeImageToSquare:img];
return img;
}
-(UIImage*)resizeImageToSquare:(UIImage*)_temp {
UIImage *img;
int w = _temp.size.width;
int h = _temp.size.height;
CGRect rect;
if (w>h) {
rect = CGRectMake((w-h)/2,0,h,h);
} else {
rect = CGRectMake(0, (h-w)/2, w, w);
}
//
img = [self crop:_temp inRect:rect];
return img;
}
-(UIImage*) crop:(UIImage*)image inRect:(CGRect)rect{
UIImage *sourceImage = image;
CGRect selectionRect = rect;
CGRect transformedRect = TransformCGRectForUIImageOrientation(selectionRect, sourceImage.imageOrientation, sourceImage.size);
CGImageRef resultImageRef = CGImageCreateWithImageInRect(sourceImage.CGImage, transformedRect);
UIImage *resultImage = [[UIImage alloc] initWithCGImage:resultImageRef scale:1.0 orientation:image.imageOrientation];
CGImageRelease(resultImageRef);
return resultImage;
}
And in my detection class I have:
- (id)initWithSampleImage:(UIImage*)sampleImage {
if ((self = [super init])) {
_frame = new CVMatOpaque();
_histograms = new CVMatNDOpaque[kGridSize *
kGridSize];
[self extractFrameFromImage:sampleImage];
}
return self;
}
- (void)extractFrameFromImage:(UIImage*)sampleImage {
CGImageRef imageRef = [sampleImage CGImage];
CVImageBufferRef imageBuffer = [self pixelBufferFromCGImage:imageRef];
CVPixelBufferLockBaseAddress(imageBuffer, 0);
// Collect some information required to extract the frame.
void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
size_t height = CVPixelBufferGetHeight(imageBuffer);
size_t width = CVPixelBufferGetWidth(imageBuffer);
// Extract the frame, convert it to grayscale, and shove it in _frame.
cv::Mat frame(height, width, CV_8UC4, baseAddress, bytesPerRow);
cv::cvtColor(frame, frame, CV_BGR2GRAY);
_frame->matrix = frame;
CVPixelBufferUnlockBaseAddress(imageBuffer, 0);
CGImageRelease(imageRef);
}
- (CVPixelBufferRef) pixelBufferFromCGImage: (CGImageRef) image
{
CVPixelBufferRef pxbuffer = NULL;
int width = CGImageGetWidth(image)*2;
int height = CGImageGetHeight(image)*2;
NSMutableDictionary *attributes = [NSMutableDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:kCVPixelFormatType_32ARGB], kCVPixelBufferPixelFormatTypeKey, [NSNumber numberWithInt:width], kCVPixelBufferWidthKey, [NSNumber numberWithInt:height], kCVPixelBufferHeightKey, nil];
CVPixelBufferPoolRef pixelBufferPool;
CVReturn theError = CVPixelBufferPoolCreate(kCFAllocatorDefault, NULL, (__bridge CFDictionaryRef) attributes, &pixelBufferPool);
NSParameterAssert(theError == kCVReturnSuccess);
CVReturn status = CVPixelBufferPoolCreatePixelBuffer(NULL, pixelBufferPool, &pxbuffer);
NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);
CVPixelBufferLockBaseAddress(pxbuffer, 0);
void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
NSParameterAssert(pxdata != NULL);
CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(pxdata, width,
height, 8, width*4, rgbColorSpace,
kCGImageAlphaNoneSkipFirst);
NSParameterAssert(context);
/* here is the problem: */
CGContextDrawImage(context, CGRectMake(0, 0, width, height), image);
CGColorSpaceRelease(rgbColorSpace);
CGContextRelease(context);
CVPixelBufferUnlockBaseAddress(pxbuffer, 0);
return pxbuffer;
}
With Instrument I found out that the problem is with CVPixelBufferRef allocations but I don't understand why - can someone see the problem?
Thank you

Answer 1

In -pixelBufferFromCGImage:, both pxBuffer and pixelBufferPool are not released. That makes sense for pxBuffer, as it is a return value, but not for pixelBufferPool – you create and leak one per call of the method.
A quick fix should be to
Release pixelBufferPool in -pixelBufferFromCGImage:
Release pxBuffer (the return value of -pixelBufferFromCGImage:) in -extractFrameFromImage:
You should also rename -pixelBufferFromCGImage: to -createPixelBufferFromCGImage: to make clear that it returns a retained object.