Memory leak with UIImage method "drawInRect" - ios

Question

I have question about correct using UIImage and method drawInRect.
I use iPad 4,Xcode Version 6.1.1, IOS 8.1.2 and I used ARC and I have tried without ARC
So, I have image "1.jpg".
Image Properties:
Dimension: 7500 x 8871 pixels
Resolution: 72 pixels/inch
Color Space: RGB
Alpha Channel: NO
I need to rescale the original image "1.jpg"
I use this code:
UIImage *originalImage=[UIImage imageNamed:#"1.jpg"];
CGSize newSize=(CGSizeMake(4096, 4096));
originalImage=[self GetScaledImage : originalImage andSize: newSize];
//----Scaling Method----------------------//
-(UIImage *) GetScaledImage :(UIImage *) inputImage andSize :(CGSize) inputSize
{
UIImage *newImage=[[[UIImage alloc] initWithCGImage:inputImage.CGImage] autorelease];
if (newImage)
{
UIGraphicsBeginImageContext(inputSize);
[newImage drawInRect: CGRectMake(0, 0, inputSize.width, inputSize.height)];
newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}
return newImage;
}
My question:
if I use newSize: (4096, 4096)
UIImage *originalImage=[UIImage imageNamed:#"1.jpg"];
CGSize newSize=(CGSizeMake(4096, 4096));
Memory now: 3.1 MB
originalImage=[self GetScaledImage : originalImage andSize: newSize];
Memory now: 4.3 MB
and it works correct
but if I use newSize: (3000, 4096)
I have this:
UIImage *originalImage=[UIImage imageNamed:#"1.jpg"];
CGSize newSize=(CGSizeMake(3000, 4096));
Memory now: 3.1 MB
originalImage=[self GetScaledImage : originalImage andSize: newSize];
Memory now: 52 MB
and it works incorrect
and magic: if I use newSize: (4096,3000) it works correct too but (3000,4096) works incorrect
So, my question: How does it work?

Answer 1

You can solve the problem by using the following method instead.
+ (UIImage *)scaleImageWithData:(NSData *)data withSize:(CGSize)size
scale:(CGFloat)scale
orientation:(UIImageOrientation)orientation {
CGFloat maxPixelSize = MAX(size.width, size.height);
CGImageSourceRef sourceRef = CGImageSourceCreateWithData((__bridge CFDataRef)data, nil);
NSDictionary *options = #{(__bridge id)kCGImageSourceCreateThumbnailFromImageAlways:(__bridge id)kCFBooleanTrue,
(__bridge id)kCGImageSourceThumbnailMaxPixelSize:[NSNumber numberWithFloat:maxPixelSize]
};
CGImageRef imageRef = CGImageSourceCreateThumbnailAtIndex(sourceRef, 0, (__bridge CFDictionaryRef)options);
UIImage *resultImage = [UIImage imageWithCGImage:imageRef scale:scale orientation:orientation];
CGImageRelease(imageRef);
CFRelease(sourceRef);
return resultImage;
}

Answer 2

I suppose there is no magic. The CGImage object is not deallocated but owned. For this, you need to set image.CGImage to some variable and then release it with
CFRelease(cgImage);
Also try to clear graphics context after all processing done.