Memory leak with core graphics - objective-c

Question

I've been tasked to solve a memory leak with a custom objective class for a legacy app that uses garbage collection.
The class takes in NSData from a jpeg file and can thumb the image. There is a method to return a new NSData object with the newly resized image.
ImageThumber * imgt = [ImageThumber withNSData:dataObjectFromJpeg];
[imgt thumbImage:1024];
NSdata * smallImage = [imgt imageData];
[imgt thumbImage:256];
NSdata * extraSmallImage = [imgt imageData];
It does what it's supposed to do but it's been discovered that for every ImageThumber that's created it allocates a ImageIO_jpeg_Data object that's never deallocated. This was found in Instruments.
When created using ImageThumber withNSData:(NSData) it creates a CGImage and stores it in a private CGImageRef variable
I found that if thumbImage:(int) isn't called the ImageIO_jpeg_Data will deallocate when ImageThumber is deallocated which leads me to believe the problem lies somewhere within the thumbImage method. If thumbImage method is called multiple times it doesn't create extra ImageIO_jpeg_Data.
I have little experience with core graphics and garbage collection.
+(id)SAMImageDataWithNSData:(NSData *)data
{
SAMImageData * new = [[[self alloc] init] autorelease];
new.imageData = [NSMutableData dataWithData:data];
CFDataRef imgData = (CFDataRef)data;
CGDataProviderRef imgDataProvider;
imgDataProvider = CGDataProviderCreateWithCFData(imgData);
new->_cgImageRef = CGImageCreateWithJPEGDataProvider(imgDataProvider, NULL, true, kCGRenderingIntentDefault);
CGDataProviderRelease(imgDataProvider);
int width = (int)CGImageGetWidth(new->_cgImageRef);
int height = (int)CGImageGetHeight(new->_cgImageRef);
new.originalSize = NSMakeSize(width, height);
return new;
}
-(void)thumbImage:(int)length
{
/* simple logic to calculate new width and height */
//If the next line is commented out the problem doesn't exist.
//You just don't get the image resize.
[self resizeCGImageToWidth:newSize.width andHeight:newSize.height];
CFMutableDataRef workingData = (CFMutableDataRef)[[NSMutableData alloc] initWithCapacity:0];
CGImageDestinationRef dest;
dest = CGImageDestinationCreateWithData(workingData,kUTTypeJPEG,1,NULL);
CGImageDestinationAddImage(dest,_cgImageRef,NULL);
CGImageDestinationFinalize(dest);
CFRelease(dest);
self.imageData = (NSMutableData *)workingData;
}
This where I believe the problem exists:
- (void)resizeCGImageToWidth:(int)width andHeight:(int)height {
CGColorSpaceRef colorspace = CGImageGetColorSpace(_cgImageRef);
CGContextRef context = CGBitmapContextCreate(NULL, width, height,
CGImageGetBitsPerComponent(_cgImageRef),
CGImageGetBytesPerRow(_cgImageRef),
colorspace,
kCGImageAlphaPremultipliedFirst);
CGColorSpaceRelease(colorspace);
if(context == NULL)
return;
CGContextDrawImage(context, CGRectMake(0, 0, width, height), _cgImageRef);
_cgImageRef = CGBitmapContextCreateImage(context);
CGContextRelease(context);
}