How To Properly Compress UIImages At Runtime

Question

I need to load 4 images for simultaneous editing. When I load them from the users library, the memory exceeds 500mb and crashes.

Here is a log from a raw allocations

Answer 1

I ended up hard coding a size reduction before processing the image. Here is the code:

PHImageManager.defaultManager().requestImageForAsset(asset, targetSize:CGSizeMake(CGFloat(asset.pixelWidth), CGFloat(asset.pixelHeight)), contentMode: .AspectFill, options: options)
{
  result, info in
  var minRatio:CGFloat = 1
  //Reduce file size so take 1/2 UIScreen.mainScreen().bounds.width/2 || CGFloat(asset.pixelHeight) > UIScreen.mainScreen().bounds.height/2)
  {
    minRatio = min((UIScreen.mainScreen().bounds.width/2)/(CGFloat(asset.pixelWidth)), ((UIScreen.mainScreen().bounds.height/2)/CGFloat(asset.pixelHeight)))
  }

  var size:CGSize = CGSizeMake((CGFloat(asset.pixelWidth)*minRatio),(CGFloat(asset.pixelHeight)*minRatio))
  UIGraphicsBeginImageContextWithOptions(size, false, 0.0)
  result.drawInRect(CGRectMake(0, 0, size.width, size.height))
  var final = UIGraphicsGetImageFromCurrentImageContext()
  var image = iImage(uiimage: final)
}

Answer 2

The reason you're having crashes and seeing such high memory usage is that you are missing the call to UIGraphicsEndImageContext(); -- so you are leaking memory like crazy.

For every call to UIGraphicsBeginImageContextWithOptions, make sure you have a call to UIGraphicsEndImageContext (after UIGraphicsGetImage*).

Also, you should wrap in @autorelease (I'm presuming you're using ARC), otherwise you'll still have out-of-memory crashes if you are rapidly processing images.

Do it like this:

@autorelease {
  UIGraphicsBeginImageContextWithOptions(...);
  ..
  something = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
}