Generate image thumbnail from existing CGImage with ImageIO? - ios

Question

I am trying to generate a thumbnail from an existing CGImage with the help of the function CGImageSourceCreateThumbnailAtIndex.
In all examples that I found the provided image source is created with the help of the image's url.
Since I don't have any URLs -only the image data- I tried like this:
func createThumbnailForImage(image: CGImage, size: Int) -> CGImage?
{
var provider = CGImageGetDataProvider(image)
if let imageSource = CGImageSourceCreateWithDataProvider(provider, nil)
{
let swiftDict = [
kCGImageSourceThumbnailMaxPixelSize as String : size,
kCGImageSourceCreateThumbnailFromImageIfAbsent as String : true
]
let nsDict = swiftDict as NSDictionary
let cfDict = nsDict as CFDictionary
return CGImageSourceCreateThumbnailAtIndex(imageSource, 0, cfDict)
}
return nil
}
The result I get is always nil.
My guess is that something is wrong with the image source but cannot really identify the problem.

Answer 1

There are implementation thumbnail generation for Swift 3
import Foundation
import UIKit
import ImageIO
class PhotoUtils: NSObject {
static func thumbnail(url:CFURL) -> UIImage {
let src = CGImageSourceCreateWithURL(url, nil)
return thumbnailImage(src: src!)
}
static func thumbnail(data imageData:CFData) -> UIImage {
let src = CGImageSourceCreateWithData(imageData, nil)
return thumbnailImage(src: src!)
}
static private func thumbnailImage(src: CGImageSource) -> UIImage {
let scale = UIScreen.main.scale
let w = (UIScreen.main.bounds.width / 3) * scale
let d : [NSObject:AnyObject] = [
kCGImageSourceShouldAllowFloat : true as AnyObject,
kCGImageSourceCreateThumbnailWithTransform : true as AnyObject,
kCGImageSourceCreateThumbnailFromImageAlways : true as AnyObject,
kCGImageSourceThumbnailMaxPixelSize : w as AnyObject
]
let imref = CGImageSourceCreateThumbnailAtIndex(src, 0, d as CFDictionary)
return UIImage(cgImage: imref!, scale: scale, orientation: .up)
}
}