Memory issue in using UIImagePNGRepresentation

Question

Hi Guys 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;
}

Answer 1

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.

Answer 2

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];

...

Answer 3

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