Creating thumbnail -> ugly quality (Swift - preparingThumbnail)

Question

This is how I create a thumbnail from Data:

let image = UIImage(data: data)!
    .preparingThumbnail(of: .init(width: size, height: size))!

try image.pngData()!.write(to: url)

The data variable contains the original image. That looks good, but I want to create thumbnails from lists.

The size variable holds a value which is the same height as my Image in SwiftUI. The problem is, it looks horrible:

Thumbnail:

Original:

The 'thumbnail' is the same size as the image above, it really looks that bad on the device, it is not stretched out. What is the correct way to create a thumbnail of the same quality in iOS 15.0>?

Answer 1

Have you tried to consider the aspect ratio as well instead of just the size? Pass in the data (your let image = UIImage(data: data)! and see if that works)

func resizeImageWithAspect(image: UIImage,scaledToMaxWidth width:CGFloat,maxHeight height :CGFloat)->UIImage? {
    let oldWidth = image.size.width;
    let oldHeight = image.size.height;
    
    let scaledBy = (oldWidth > oldHeight) ? width / oldWidth : height / oldHeight;
    
    let newHeight = oldHeight * scaledBy;
    let newWidth = oldWidth * scaledBy;
    let newSize = CGSize(width: newWidth, height: newHeight)
    
    UIGraphicsBeginImageContextWithOptions(newSize,false,UIScreen.main.scale);
    
    image.draw(in: CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height));
    let newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage
}