调整图像大小而不会降低质量

Question

我正在使用下面的功能来调整图像宽度和高度,但我注意到它会破坏图像质量.

class func imageWithSize(image: UIImage,size: CGSize)->UIImage{
    if UIScreen.mainScreen().respondsToSelector("scale"){
        UIGraphicsBeginImageContextWithOptions(size,false,UIScreen.mainScreen().scale);
    }
    else
    {
        UIGraphicsBeginImageContext(size);
    }

    image.drawInRect(CGRectMake(0, 0, size.width, size.height));
    var newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return newImage;
}

class func resizeImageWithAspect(image: UIImage,scaledToMaxWidth width:CGFloat,maxHeight height :CGFloat)->UIImage
{


    let scaleFactor =  width / height;


    let newSize = CGSizeMake(width, height);

    return imageWithSize(image, size: newSize);
}

还有另一种方法可以在不破坏质量的情况下调整图像大小吗？或者我如何修复下面的功能,以便在调整大小后不会破坏图像质量？

Answer 1

这是我在swift中的代码.对于平方图像,它工作得很好,没有任何质量损失!

extension UIImage {

    func resize(targetSize: CGSize) -> UIImage {
        return UIGraphicsImageRenderer(size:targetSize).image { _ in
            self.draw(in: CGRect(origin: .zero, size: targetSize))
        }
    }

}

Answer 2

这是我的Objective-C代码.这对我有用.

+ (UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize isAspectRation:(BOOL)aspect {
    if (!image) {
        return nil;
    }
    //UIGraphicsBeginImageContext(newSize);
    // In next line, pass 0.0 to use the current device's pixel scaling factor (and thus account for Retina resolution).
    // Pass 1.0 to force exact pixel size.
    CGFloat originRatio = image.size.width / image.size.height;
    CGFloat newRatio = newSize.width / newSize.height;

    CGSize sz;

    if (!aspect) {
        sz = newSize;
    }else {
        if (originRatio < newRatio) {
            sz.height = newSize.height;
            sz.width = newSize.height * originRatio;
        }else {
            sz.width = newSize.width;
            sz.height = newSize.width / originRatio;
        }
    }
    CGFloat scale = 1.0;
    //    if([[UIScreen mainScreen]respondsToSelector:@selector(scale)]) {
    //        CGFloat tmp = [[UIScreen mainScreen]scale];
    //        if (tmp > 1.5) {
    //            scale = 2.0;
    //        }
    //    }
    sz.width /= scale;
    sz.height /= scale;
    UIGraphicsBeginImageContextWithOptions(sz, NO, scale);
    [image drawInRect:CGRectMake(0, 0, sz.width, sz.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

我看到了你的代码Swift.我只是将我转换Objective-C为Swift没有测试.你可以尝试一下,让我知道.谢谢!

struct CommonUtils {
    static func imageWithImage(image: UIImage, scaleToSize newSize: CGSize, isAspectRation aspect: Bool) -> UIImage{

        let originRatio = image.size.width / image.size.height;//CGFloat
        let newRatio = newSize.width / newSize.height;

        var sz: CGSize = CGSizeZero

        if (!aspect) {
            sz = newSize
        }else {
            if (originRatio < newRatio) {
                sz.height = newSize.height
                sz.width = newSize.height * originRatio
            }else {
                sz.width = newSize.width
                sz.height = newSize.width / originRatio
            }
        }
        let scale: CGFloat = 1.0

        sz.width /= scale
        sz.height /= scale
        UIGraphicsBeginImageContextWithOptions(sz, false, scale)
        image.drawInRect(CGRectMake(0, 0, sz.width, sz.height))
        let newImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return newImage
    }
}

Answer 3

我刚刚使用 swift 5 创建了这个有用的 UIImage 扩展。您可以使用它来调整 UIImage 的大小，而不会损失质量。

我添加了几种方法，以便能够将图像的大小调整为宽度或高度，并保持纵横比。

extension UIImage {

    func resize(targetSize: CGSize) -> UIImage {
        return UIGraphicsImageRenderer(size:targetSize).image { _ in
            self.draw(in: CGRect(origin: .zero, size: targetSize))
        }
    }

    func resize(scaledToWidth desiredWidth: CGFloat) -> UIImage {
        let oldWidth = size.width
        let scaleFactor = desiredWidth / oldWidth

        let newHeight = size.height * scaleFactor
        let newWidth = oldWidth * scaleFactor
        let newSize = CGSize(width: newWidth, height: newHeight)

        return resize(targetSize: newSize)
    }

    func resize(scaledToHeight desiredHeight: CGFloat) -> UIImage {
        let scaleFactor = desiredHeight / size.height
        let newWidth = size.width * scaleFactor
        let newSize = CGSize(width: newWidth, height: desiredHeight)

        return resize(targetSize: newSize)
    }

}