Resize UIImage under memory constraints

Question

I have a massive UIImage downloaded from a web resource (>300MBs) which when I attempt to render is causing an app crash due to memory. I am trying to resize the image using the following code:

+ (UIImage *)imageWithImage:(UIImage *)image scaled:(float) scale {
    //UIGraphicsBeginImageContext(newSize);
    CGSize size = (CGSize){scale * image.size.width, scale * image.size.height};
    UIGraphicsBeginImageContextWithOptions(size, NO, 0.0);
    [image drawInRect:CGRectMake(0, 0, size.width, size.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

The problem is, as you may have guessed, that this requires actually rendering the image and thus causes the same crash. Is there a way to resize an large image without placing such an enormous memory strain on the system?

Answer 1

The problem is that you are holding the image in memory. Download it to disk and use the ImageIO framework to read a "thumbnail" (smaller size) directly from disk without ever having to hold the full-size image in memory.