Creating a thumbnail from UIImage using CGImageSourceCreateThumbnailAtIndex

Question

I want to use the function CGImageSourceCreateThumbnailAtIndex to create a thumbnail from an UIImage. All I have is the UIImage itself. The image is the snapshot on a UIView.

Please, I don't want to use any other method to create the thumbnail, just the one using CGImageSourceCreateThumbnailAtIndex, because I want to compare its performance with the other methods I already have.

Said that, this is the code I have so far.

I have create a UIImage category with this code:

- (UIImage *)createSquaredThumbnailWithWidth:(NSInteger)width {

  CFDictionaryRef options = (__bridge CFDictionaryRef) @{
                                                         (id) kCGImageSourceCreateThumbnailWithTransform : @YES,
                                                         (id) kCGImageSourceCreateThumbnailFromImageAlways : @YES,
                                                         (id) kCGImageSourceThumbnailMaxPixelSize : @(width)
                                                         };

  CGImageRef scaledImageRef = CGImageSourceCreateThumbnailAtIndex(????, 0, options);


  UIImage* scaled = [UIImage imageWithCGImage:scaledImageRef];

  CGImageRelease(scaledImageRef);

  return scaled;
}

My problem is with this line:

  CGImageRef scaledImageRef = CGImageSourceCreateThumbnailAtIndex(????, 0, options);

The first parameter of this function demands a CGImageSourceRef, but like I said, I just have an UIImage, that image is on memory, not on disk, and I don't want to save it to disk, or the performance will go down the drain.

How do I get a CGImageSourceRef from a UIImage that is on memory???

what about on memory? all image instances are in memory. Use it as @Nirav D said. — Muhammad Zohaib Ehsan, Nov 18 '16 at 12:24
Out of curiosity, which method for creating a thumbnail from a UIImage is the 'best' (in terms of memory usage, time etc)? — Z S, Nov 14 '18 at 19:55

score 23 · Answer 1 · answered Sep 15 '17 at 07:43

23

Swift 4 code

let imageData = UIImagePNGRepresentation(image)!
let options = [
    kCGImageSourceCreateThumbnailWithTransform: true,
    kCGImageSourceCreateThumbnailFromImageAlways: true,
    kCGImageSourceThumbnailMaxPixelSize: 300] as CFDictionary
let source = CGImageSourceCreateWithData(imageData, nil)!
let imageReference = CGImageSourceCreateThumbnailAtIndex(source, 0, options)!
let thumbnail = UIImage(cgImage: imageReference)

answered Sep 15 '17 at 07:43

Ivan Vavilov

1,520
1
15
28

This really came handy after series of web search! Thanks for this wonderful solution. – Aweda Mar 05 '18 at 10:19
1

Also review a post https://nshipster.com/image-resizing/ by mattt where he has listed many image scaling techniques and their performance benchmarks. – Vijayendra Jul 08 '20 at 14:03
How to make thumbnail image orientation not rotated, i tried by changing kCGImageSourceCreateThumbnailWithTransform to false, but still it is rotating, All i need is whether original image is of portrait or landscape , i dont need thumbnail to be rotated. – virtplay Aug 21 '20 at 14:43
@virtplay you can apply image rotation from original image: UIImage(cgImage: cgImage, scale: originalImage.scale, orientation: originalImage.imageOrientation) – snake302 Jul 10 '23 at 11:29

score 14 · Answer 2 · answered Sep 26 '19 at 12:10

Swift 5.1 extension

based on Ivan's answer

extension UIImage {

  func getThumbnail() -> UIImage? {

    guard let imageData = self.pngData() else { return nil }

    let options = [
        kCGImageSourceCreateThumbnailWithTransform: true,
        kCGImageSourceCreateThumbnailFromImageAlways: true,
        kCGImageSourceThumbnailMaxPixelSize: 300] as CFDictionary

    guard let source = CGImageSourceCreateWithData(imageData as CFData, nil) else { return nil }
    guard let imageReference = CGImageSourceCreateThumbnailAtIndex(source, 0, options) else { return nil }

    return UIImage(cgImage: imageReference)

  }
}

.jpegData(compressionQuality: 0.95) is faster than .pngData() while providing almost the same quality — Ivan Nikitin, Apr 21 '22 at 17:25

score 12 · Accepted Answer · edited Jul 15 '22 at 10:46

Have you try using CGImageSourceCreateWithData and passing image data as CFDataRef like this:

Note: Using CGImageSourceCreateWithData loses information about image rotation, use the CGImageSourceCreateWithURL for hassle free rotation of final image.

NSData *imageData = UIImagePNGRepresentation(image);
CGImageSourceRef src = CGImageSourceCreateWithData((__bridge CFDataRef)imageData, NULL);
CFDictionaryRef options = (__bridge CFDictionaryRef) @{
                                                     (id) kCGImageSourceCreateThumbnailWithTransform : @YES,
                                                     (id) kCGImageSourceCreateThumbnailFromImageAlways : @YES,
                                                     (id) kCGImageSourceThumbnailMaxPixelSize : @(width)
                                                     };

CGImageRef scaledImageRef = CGImageSourceCreateThumbnailAtIndex(src, 0, options);
CFRelease(src);
UIImage *scaled = [UIImage imageWithCGImage:scaledImageRef];
CGImageRelease(scaledImageRef);
return scaled;

Note: If you have URL of image then you can create CGImageSourceRef using CGImageSourceCreateWithURL.

CGImageSourceRef src = CGImageSourceCreateWithURL((__bridge CFURLRef)(imageFileURL), NULL);

@Pang If you are facing memory leak than try once releasing src object. — Nirav D, Mar 29 '18 at 05:54
One of the least memory intensive options I've come across. Very useful, thank you. — dezinezync, Dec 19 '18 at 07:11

score 0 · Answer 4 · answered Aug 23 '22 at 12:30

0

Swift and iOS 15

func preparingThumbnail(of size: CGSize) -> UIImage?

Example would be:

let image = UIImage(named: "info")
image.preparingThumbnail(of size: CFSize(width: 300, height: 400))

answered Aug 23 '22 at 12:30

Wladislaw

1,200
2
12
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how to preserve aspect ratio? current it is not preserving – Rashesh Bosamiya Apr 20 '23 at 07:45

Creating a thumbnail from UIImage using CGImageSourceCreateThumbnailAtIndex

4 Answers4

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