使用CGImageSourceCreateThumbnailAtIndex从UIImage创建缩略图

Question

我想使用该函数CGImageSourceCreateThumbnailAtIndex从一个创建一个缩略图UIImage.我所拥有的就是它UIImage自己.图像是a上的快照UIView.

请,我不想使用任何其他方法来创建缩略图,只是使用缩略图CGImageSourceCreateThumbnailAtIndex,因为我想将其性能与我已有的其他方法进行比较.

说,这是我到目前为止的代码.

我UIImage用这段代码创建了一个类别:

- (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;
}

我的问题在于这一行:

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

这个函数的第一个参数需要一个CGImageSourceRef,但就像我说的,我只是有一个UIImage,那个图像是在内存上,而不是在磁盘上,我不想将它保存到磁盘上,或者性能会下降.

我怎么CGImageSourceRef从UIImage内存中得到一个？

Answer 1

Swift 4代码

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)

Answer 2

Swift 5.1 扩展

基于伊万的回答

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)

  }
}

Answer 3

您是否尝试CGImageSourceCreateWithData过CFDataRef像这样使用和传递图像数据.

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);
UIImage *scaled = [UIImage imageWithCGImage:scaledImageRef];
CGImageRelease(scaledImageRef);
return scaled;

注意:如果您有URL图像,则可以CGImageSourceRef使用创建CGImageSourceCreateWithURL.

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