Rendering 60 images causing memory warning

Question

I'm rendering 60 images and getting a memory warning. Is there a better approach to my code below?

- (void)change{
    for (int aniCount = 1; aniCount < 60; aniCount++) {
        if ([UIScreen mainScreen].bounds.size.height == 568) {
           self.renderString = [NSString stringWithFormat: @"%i_5.png", aniCount + 1];
           self.imageView.image = [UIImage imageNamed:@"1_5.png"];
        }else{
            self.renderString =  [NSString stringWithFormat: @"%i.png", aniCount + 1];
        }
        // here is the code to pre-render the image
        UIImage *frameImage = [UIImage imageNamed:self.renderString];
        UIGraphicsBeginImageContext(frameImage.size);
        CGRect rect = CGRectMake(0, 0, frameImage.size.width, frameImage.size.height);
        [frameImage drawInRect:rect];
        UIImage *renderedImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();

        [self.menuanimationImages addObject:renderedImage];
    }

    self.imageView.animationImages = [NSArray arrayWithArray: self.menuanimationImages];
 }

This method is called in my - (void)viewDidLoad

An example of what the app screen looks like: https://www.youtube.com/watch?v=2f80UcLhOW8

Answer 1

Do we infer from the check of the screen resolution that these are full screen images? If so, to do a full screen animation with 60 images requires an extraordinary amount of memory, and I'm not surprised you'd get memory warnings. Each image, when used in a UIImageView will require at least four bytes per pixel.

For non-retina images on 4" screen, that would require roughly 42mb for 60 full screen images. If those are retina images (with twice the resolution) that jumps to 166mb. Don't look at the size of the PNG files when considering the amount of memory used, because PNG files have some compression, but they'll be uncompressed when you use them in your app.

Generally you would not want to animate use that many full screen images. You would want to probably consider programmatically animating the view using UIKit animation or Core Animation (or other similar technologies). Or, if you really have to use a sequence of images, see if you can constrain the portion that's animated to a smaller portion of the screen, thus using smaller images and requiring far less memory.

It's hard to say without knowing what the animation looks like. If you describe the animation (or show us a screen snapshot or two), we can probably suggest far less memory intensive approaches.

---

In your comments you shared a link to a video that features the desired kaleidoscopic effect. A couple of thoughts:

1. I'd first focus on programmatic ways to render kaleidoscopic effects. Given the complexity here, this might lead me to research "OpenGL ES" approaches for rendering this kaleidoscopic effect. You might even chance upon some existing implementations.

2. I notice that there are Core Image filters for CIKaleidoscope and CITriangleKaleidoscope that might be useful in generating the effect you're looking for (see the Core Image Filter Reference for information on those two filters). I don't think those will be quite right here, but work checking out.

3. Failing the above attempts to programmatically render the kaleidoscope, it strikes me that, at the very least, you could reduce memory requirements of your current implementation by a factor of four given that the the kaleidoscope-effect seems to be both horizontally and vertically symmetric. So you could theoretically have a sequence of images for the upper left quadrant, and then render the other three as transforms of the same image.

4. Or you could alternatively create a full screen video and use the media player framework to play it.

I'd probably exhaust those lines of inquiry before I pursued doing a animation via a sequence of full screen images. The full screen images is just going to be a memory inefficient way to tackle this sort of problem, and you're almost certainly likely to run into challenges. And if you ever consider iPad rendition of the app or want to consider longer sequences, the approach of a series of full screen images is likely to be entirely untenable.