Animating retina images - objective-c

Question

I'm trying to animate some images. The images are working well on non-retina iPads but their retina counterparts are slow and the animations will not cycle through at the specified rate. The code i'm using is below with the method called every 1/25th second. This method appears to perform better than UIViewAnimations.
if (counter < 285) {
NSString *file = [[NSBundle mainBundle] pathForResource:[NSString stringWithFormat:#"Animation HD1.2 png sequence/file_HD1.2_%d", counter] ofType:#"png"];
#autoreleasepool {
UIImage *someImage = [UIImage imageWithContentsOfFile:file];
falling.image = someImage;
}
counter ++;
} else {
NSLog(#"Timer invalidated");
[timer invalidate];
timer = nil;
counter = 1;
}
}
I realise there are a lot of images but the performance is the same for animations with less frames. Like i said, the non-retina animations work well. Each image above is about 90KB. Am i doing something wrong or is this simply a limitation of the iPad? To be honest, i find it hard to believe that it couldn't handle something like this when it can handle the likes of complex 3D games so i imagine i'm doing something wrong. Any help would be appreciated.
EDIT 1:
From the answers below, I have edited my code but to no avail. Executing the code below results in the device crashing.
in viewDidLoad
NSString *fileName;
myArray = [[NSMutableArray alloc] init];
for(int i = 1; i < 285; i++) {
fileName = [NSString stringWithFormat:#"Animation HD1.2 png sequence/HD1.2_%d.png", i];
[myArray addObject:[UIImage imageNamed:fileName]];
NSLog(#"Loaded image: %d", i);
}
falling.userInteractionEnabled = NO;
falling.animationImages = humptyArray;
falling.animationDuration = 11.3;
falling.animationRepeatCount = 1;
falling.contentMode = UIViewContentModeCenter;
the animation method
-(void) triggerAnimation {
[falling startAnimating];
}

Answer 1

First of all, animation performance on the retina iPad is notoriously choppy. That said, there are a few things you could do to make sure your getting the best performance for your animation (in no particular order).
Preloading the images - As some others have mentioned, your animation speed suffers when you have to wait for the reading of your image before you draw it. If you use UIImageView's animation properties this preloading will be taken care of automatically.
Using the right image type - Despite the advantage in file size, using JPEGs instead of PNGs will slow your animation down significantly. PNGs are less compressed and are easier for the system to decompress. Also, Apple has significantly optimized the iOS system for reading and drawing PNG images.
Reducing Blending - If at all possible, try and remove any transparency from your animation images. Make sure there is no alpha channel in your images even if it seems completely opaque. You can verify by opening the image in Preview and opening the inspector. By reducing or removing these transparent pixels, you eliminate extra rendering passes the system has to do when displaying the image. This can make a significant difference.
Using a GPU backed animation - Your current method of using a timer to animate the image is not recommended for optimal performance. By not using UIViewAnimation or CAAnimation you are forcing the CPU to do most of the animation work. Many of the animation techniques of Core Animation and UIViewAnimation are optimized and backed by OpenGL which using the GPU to process images and animate. Graphics processing is what the GPU is made for and by utilizing it you will maximize your animation performance.
Avoiding pixel misalignment - Make sure your animation images are at the right size on screen when displaying them. If you are stretching your image while animating or using an incorrect frame, the system has to do more work to process each frame. Also, using whole numbers for any frame or point values will keep from anti-aliasing when the system tries to position an image on a fractional pixel.
Be wary of shadows and rounded corners - CALayer has lots of easy ways to create shadows and rounded corners, but if you are moving these layers in animations, often times the system will redraw the layer in each frame of the animation. This is the case when specifying a shadow using the shadowOffset property (using UILabel's shadow properties will not render every frame). Also, borders and using maskToBounds and clipToBounds will be more performance intensive rather than just using an image editor to crop the actual asset.

Answer 2

There are a few things to notice here:
If "falling" is UIImageView, make sure it's content mode says something like "center" and not some sort of scaling (make sure your images fit it, of course).
Other than that, as #FogleBird said, test if your device have enough memory to preload all images, if not, try to at least preload the data by creating NSData objects with the image files.
Your use of #autorelease pool is not very useful, you end up creating an auto release object that does a single thing - remove a reference to an already retained object - no memory gain, but performance loss.
If anything, you should have wrapped the file name formatter code, and considering this method is called by an NSTimer, it is already wrapped in an autorelease pool.

Answer 3

just wanted to point out - when you are creating the NSString with the image name - what is the "Animation HD1.2 png sequence/HD1.2_%d.png" ?
It looks likey you are trying to put a path there, try just the image name - eg. "HD1.2_%d.png".