Large Image Processing (ARC) Major memory leaks - objective-c

Question

My iPad app that I am creating has to be able to create the tiles for a 4096x2992 image that is generated earlier in my app..
4096x2992 image isn't very complex (what i'm testing with) and when written to file in png format is approximately 600kb...
On the simulator, this code seems to work fine however when I run the app in tighter memory conditions (on my iPad) the process quits because it ran out of memory...
I've been using the same code in the app previously what was working fine (was only creating tiles for 3072x2244 images however)...
Either I must be doing something stupidly wrong or my #autoreleasepool's aren't working as they should (i think i mentioned that im using ARC)... When running in instruments I can just see the memory used climb up until ~500mb where it then crashes!
I've analysed the code and it hasn't found a single memory leak related to this part of my app so I'm really confused on why this is crashing on me...
Just a little history on how my function gets called so you know whats happening... The app uses CoreGraphics to render a UIView (4096x2992) with some UIImageView's inside it then it sends that UIImage reference into my function buildFromImage: (below) where it begins cutting up/resizing the image to create my file...
Here is the buildFromImage: code... the memory issues are built up from within the main loop under NSLog(#"LOG ------------> Begin tile loop ");...
-(void)buildFromImage:(UIImage *)__image {
NSLog(#"LOG ------------> Begin Build ");
//if the __image is over 4096 width of 2992 height then we must resize it! (stop crashes ect)
if (__image.size.width > __image.size.height) {
if (__image.size.width > 4096) {
__image = [self resizeImage:__image toSize:CGSizeMake(4096, (__image.size.height * 4096 / __image.size.width))];
}
} else {
if (__image.size.height > 2992) {
__image = [self resizeImage:__image toSize:CGSizeMake((__image.size.width * 2992 / __image.size.height), 2992)];
}
}
//create preview image (if landscape, no more than 748 high... if portrait, no more than 1004 high) must keep scale
NSString *temp_archive_store = [[NSString alloc] initWithFormat:#"%#/%i-temp_imgdat.zip",NSTemporaryDirectory(),arc4random()];
NSString *temp_tile_store = [[NSString alloc] initWithFormat:#"%#/%i-temp_tilestore/",NSTemporaryDirectory(),arc4random()];
//create the temp dir for the tile store
[[NSFileManager defaultManager] createDirectoryAtPath:temp_tile_store withIntermediateDirectories:YES attributes:nil error:nil];
//create each tile and add it to the compressor once its made
//size of tile
CGSize tile_size = CGSizeMake(256, 256);
//the scales that we will be generating the tiles too
NSMutableArray *scales = [[NSMutableArray alloc] initWithObjects:[NSNumber numberWithInt:1000],[NSNumber numberWithInt:500],[NSNumber numberWithInt:250],[NSNumber numberWithInt:125], nil]; //scales to loop round over
NSLog(#"LOG ------------> Begin tile loop ");
#autoreleasepool {
//loop through the scales
for (NSNumber *scale in scales) {
//scale the image
UIImage *imageForScale = [self resizedImage:__image scale:[scale intValue]];
//calculate number of rows...
float rows = ceil(imageForScale.size.height/tile_size.height);
//calulate number of collumns
float cols = ceil(imageForScale.size.width/tile_size.width);
//loop through rows and cols
for (int row = 0; row < rows; row++) {
for (int col = 0; col < cols; col++) {
NSLog(#"LOG ------> Creating Tile (%i,%i,%i)",col,row,[scale intValue]);
//build name for tile...
NSString *tile_name = [NSString stringWithFormat:#"%#_%i_%i_%i.png",#"image",[scale intValue],col,row];
#autoreleasepool {
//build tile for this coordinate
UIImage *tile = [self tileForRow:row column:col size:tile_size image:imageForScale];
//convert image to png data
NSData *tile_data = UIImagePNGRepresentation(tile);
[tile_data writeToFile:[NSString stringWithFormat:#"%#%#",temp_tile_store,tile_name] atomically:YES];
}
}
}
}
}
}
Here are my resizing/cropping functions too as these could also be causing the issue..
-(UIImage *)resizeImage:(UIImage *)inImage toSize:(CGSize)scale {
#autoreleasepool {
CGImageRef inImageRef = [inImage CGImage];
CGColorSpaceRef clrRf = CGColorSpaceCreateDeviceRGB();
CGContextRef ctx = CGBitmapContextCreate(NULL, ceil(scale.width), ceil(scale.height), CGImageGetBitsPerComponent(inImageRef), CGImageGetBitsPerPixel(inImageRef)*ceil(scale.width), clrRf, kCGImageAlphaPremultipliedFirst );
CGColorSpaceRelease(clrRf);
CGContextDrawImage(ctx, CGRectMake(0, 0, scale.width, scale.height), inImageRef);
CGImageRef img = CGBitmapContextCreateImage(ctx);
UIImage *image = [[UIImage alloc] initWithCGImage:img scale:1 orientation:UIImageOrientationUp];
CGImageRelease(img);
CGContextRelease(ctx);
return image;
}
}
- (UIImage *)tileForRow: (int)row column: (int)col size: (CGSize)tileSize image: (UIImage*)inImage
{
#autoreleasepool {
//get the selected tile
CGRect subRect = CGRectMake(col*tileSize.width, row * tileSize.height, tileSize.width, tileSize.height);
CGImageRef inImageRef = [inImage CGImage];
CGImageRef tiledImage = CGImageCreateWithImageInRect(inImageRef, subRect);
UIImage *tileImage = [[UIImage alloc] initWithCGImage:tiledImage scale:1 orientation:UIImageOrientationUp];
CGImageRelease(tiledImage);
return tileImage;
}
}
Now I never use to be that good with memory management, so I did take the time to read up on it and also converted my project to ARC to see if that could address my issues (that was a while ago) but from the results i get after profiling it in instruments I must be doing something STUPIDLY wrong for the memory to leak as bad as it does but I just can't see what i'm doing wrong.
If anybody can point out anything I may be doing wrong it would be great!
Thanks
Liam
(let me know if you need more info)

Answer 1

I use "UIImage+Resize". Inside #autoreleasepool {} it works fine with ARC in a loop.
https://github.com/AliSoftware/UIImage-Resize
-(void)compress:(NSString *)fullPathToFile {
#autoreleasepool {
UIImage *fullImage = [[UIImage alloc] initWithContentsOfFile:fullPathToFile];
UIImage *compressedImage = [fullImage resizedImageByHeight:1024];
NSData *compressedData = UIImageJPEGRepresentation(compressedImage, 75.0);
[compressedData writeToFile:fullPathToFile atomically:NO];
}
}