Memory issue in using UIImagePNGRepresentation

Question

I found this module to be troublesome. I import more than 100 images from Photolibrary, save them in documents directory with a different name. As expected I had a memory issue in the unusual place. It seems UIImagePNGRepresenation is caching files. So when I run the below process for 300+ images, I see "Overall bytes" in the range of 3.00 GB and crashes due to Memory (tested in allocations tool). I have pasted the code below. Is there any alternative for this code

-(void)something
{
   NSData *data=nil;
   for (int i=0; i<numberOfImages; i++) {
    
    @autoreleasepool {
        
        UIImage *image=[UIImage imageNamed:[NSString stringWithFormat:@"image%d.png",i]];
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        
        NSString *documentsDirectory = [[paths objectAtIndex:0] stringByAppendingString:@"directoryname"];
        
        NSString *fullPath = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"image%d.png",i]];
        
        //convert image into .png format
        data=UIImagePNGRepresentation(image);
        [data writeToURL:[NSURL URLWithString:fullPath] atomically:NO];
      }
   }
   data=nil;
}

Woodbridge

Answer 1

I mailed this issue to Apple and they asked me to introduce sleep cycles between every allocation. Add sleep before allocation.

Woodbridge

I also tried this but not helpful..Please provide other way to solve this...Thanks in advance – Sodium

Answer 2

I solve this issue by sending a 4 channels image (RGBA or RGBX) instead of a 3 channels image (RGB).

You can check if there's any chance to change parameters of your image.

Whyalla

Answer 3

The caching is coming from [UIImage imageNamed:], not UIImagePNGRepresentation(). Do this instead:

NSString *imageName = [NSString stringWithFormat:@"image%d.png", i];
NSString *imagePath = [[NSBundle mainBundle] pathForResource:imageName];
UIImage *image = [UIImage imageWithContentsOfFile:imagePath];

...

Michaelamichaele

No. It did not work. I tried with [UIImage imageWithContentsOfFile:], [[UIImage alloc]initWithContentsOfFile:]. The issue is during conversion of UIImage to NSData. I checked the above some 15 times – Woodbridge

Ok, well seen as you're not using the images anyway, and they're pngs to start with, why not just copy them? [NSFileManager copyItemAtPath:toPath:error:] – Michaelamichaele

Great Idea..! I will check that now – Woodbridge

No it did not work. Assets URL are different from normal one. – Woodbridge

You can copy the raw data using ALAssetRepresentation. The downside is photos are typically JPEG, not PNG. – Hildegardehildesheim