How To Properly Compress UIImages At Runtime - ios

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 dump before I did any compression attempts:
Code:
var pickedImage = UIImage(data: imageData)
Instrument:
I have read several posts on compressing UIImages. I have tried reducing the UIImage:
New Code:
var pickedImage = UIImage(data: imageData, scale:0.1)
Instrument:
Reducing the scale of the UIImage had NO EFFECT?! Very odd.
So now I tried creating a JPEG compression based on the full UIImage
New code:
var pickedImage = UIImage(data: imageData)
var compressedData:NSData = UIImageJPEGRepresentation(pickedImage,0)
var compressedImage:UIImage = UIImage(data: compressedData)!//this is now used to display
Instrument:
Now, I suspect because I am converting the image its still being loaded. And since this is all occuring inside a callback from PHImageManager, I need a way to create a compressed UIImage from the NSData, but the setting the scale to 0.1 did NOTHING.
So any suggestions as to how I can compress this UIImage right from the NSData would be life saving!!!
Thanks

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();
}