Convert UIImage to NSData increase the size of the original image

Number:rdar://FB5986565 Date Originated:24/05/2016
Status:Open Resolved:
Product:iOS SDK Product Version:
Classification:No Value Reproducible:Always
When you convert a NSData to UIImage and back to NSData, the size of the image increases and the API do not provide a way to apply the same compression level of the original NSData, for some cases, even using the max compression of UIImageJPEGRepresentation.

Steps to Reproduce:
1. Download an image from an URL or load it from the assets
2. Convert the NSData to UIImage
3. Convert the UIImage to NSData using UIImageJPEGRepresentation or UIImagePNGRepresentation

Expected Results:
The API should provide a method to convert the UIImage to NSData using the same compression of the original NSData

Actual Results:
The NSData result of the conversion is always bigger than the original NSData. For some images, the compression level on UIImageJPEGRepresentation may result on a data with smaller size or close to the original size, but the process to achieve it losing quality as less as possible is not simple.

It can be seen using the example provided. That results on the follow:

Original data: 16456 b


- JPEG compressionQuality 1.0 image: 56647 b
- JPEG compressionQuality 0.0 image: 24628 b


- PNG image: 53419 b



- CF JPEG compressionQuality 1.0 image: 56647 b
- CF JPEG compressionQuality 0.0 image: 24628 b


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