UIGraphicsImageContext Memory Spike - Reducing Footprint

Question

I have a UIImage Category for iOS Objective-C which tints an image based on a given UIColor value. You can take a look at the method below:

- (UIImage *)tintImageWithTint:(UIColor *)color withIntensity:(float)alpha {
 CGSize size = self.size;
 UIGraphicsBeginImageContextWithOptions(size, NO, [UIScreen mainScreen].scale); // MEMORY SPIKE
 CGContextRef context = UIGraphicsGetCurrentContext();
 [self drawAtPoint:CGPointZero blendMode:kCGBlendModeNormal alpha:1.0]; // MEMORY SPIKE
 CGContextSetFillColorWithColor(context, color.CGColor);
 CGContextSetBlendMode(context, kCGBlendModeOverlay);
 CGContextSetAlpha(context, alpha);
 CGContextFillRect(UIGraphicsGetCurrentContext(), CGRectMake(CGPointZero.x, CGPointZero.y, self.size.width, self.size.height));
 // Get the resized image from the context and a UIImage
 CGImageRef newImageRef = CGBitmapContextCreateImage(context); // MEMORY SPIKE
 UIImage *tintedImage = [UIImage imageWithCGImage:newImageRef];
 CGImageRelease(newImageRef);
 UIGraphicsEndImageContext();
 return tintedImage;
}

I've been testing this method with Xcode's Instruments app and found that it takes up more than 96.0 % of all bytes used during the life cycle of the app. That's crazy! It allocates more than 5 MB very quickly, which causes a level one memory warning and begins to terminate other running processes.

Instruments Allocation Analysis

The image that I'm tinting is only a 111 KB, so I can't see how this code could possibly allocate more than 5 MB so quickly.

How can I improve the performance of this code and reduce its memory impact? I'm not very familiar with CoreGraphics, so any help would be appreciated.

Answer 1

your image might have 111 KB compressed as an jpg or a png. But for image processing it needs to be decompressed. It will be loaded into memory with 8 or 16 bit for each color channel. With RGB it would be up to 48 bit per pixel and 8 bit for the alpha cannel in case of png. So 5MB would represent roughly 1.25 million pixel, or something like 1000*1250 pixel.

Answer 2

You could use this approach on iOS 7 devices. I can't see which images you're using, so I don't know if this will be an actual improvement for you, but the new UIView methods are supposedly ultra-performant:

- (UIImage *)tintImageWithTint:(UIColor *)color withIntensity:(float)alpha {
 CGRect frame = CGRectMake(0, 0, self.size.width, self.size.height);
 UIView *view = [[UIView alloc] initWithFrame:frame];
 UIImageView *imageView = [[UIImageView alloc] initWithImage:self];
 UIView *tintView = [[UIView alloc] initWithFrame:frame];
 tintView.backgroundColor = color;
 tintView.alpha = alpha;
 [view addSubview:imageView];
 [view addSubview:tintView];
 UIGraphicsBeginImageContextWithOptions(self.size, NO, [UIScreen mainScreen].scale);
 [view drawViewHierarchyInRect:view.bounds afterScreenUpdates:YES];
 UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
 UIGraphicsEndImageContext();
 return image;
}

• Malachi: could you explain your review a little more please?
• Aaron Brager: @Malachi I'd be happy to. Are there specific questions I should answer?
• Malachi: you could explain why these are more performant, or how it works, etc. I don't code in Objective C or do anything for Apple Devices, but I know that we like our reviews to have a little more information in them.