Why does my UIImage take up so much memory?

Question

I have a UIImage that I'm loading into one of my app's views. It is a 10.7 MB image, but when it loads in the app, the app's resource usage suddenly jumps by 50 MB. Why does it do this? Shouldn't memory used increase by only about 10.7MB? I am certain that loading the image is what causes the jump in memory usage because I tried commenting these lines out and the memory usage went back to around 8 MB. Here's how I load the image:

UIImage *image = [UIImage imageNamed:@"background.jpg"];
self.backgroundImageView = [[UIImageView alloc] initWithImage:image];
[self.view addSubview:self.backgroundImageView];

If there is no way to decrease the memory used by this image, is there a way to force it to deallocate when I want it to? I'm using ARC.

Answer 1

No, it should not be 10.7MB. The 10.7MB is the compressed size of the image. The image loaded in to the UIImage object is a decoded image.

For each pixel in the image 4 bytes (R,G,B and Alpha) are used, therefore you can calculate the memory size, height x width x 4 = total bytes in memory.

So the moment you loaded the image into memory it will take up lots of memory, and since a UIImageView is used to present the image and as a subview the images is kept in memory.

You should try and change the size of the image to match the size of the iOS screen size.

Answer 2

As @rckoenes said Don't show the images with high file size. You need to resize the image before you display it.

UIImage *image = [UIImage imageNamed:@"background.jpg"];
self.backgroundImageView =[self imageWithImage:display scaledToSize:CGSizeMake(20, 20)];//Give your CGSize of the UIImageView.
[self.view addSubview:self.backgroundImageView];


-(UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize {
    //UIGraphicsBeginImageContext(newSize);
    // In next line, pass 0.0 to use the current device's pixel scaling factor (and thus account for Retina resolution).
    // Pass 1.0 to force exact pixel size.
    UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);
    [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}