在我的iPhone应用程序中，我用相机拍了一张照片，然后我想把它调整为290*390像素。我用这个方法来调整图像的大小:
UIImage *newImage = [image _imageScaledToSize:CGSizeMake(290, 390)
interpolationQuality:1];
它工作得很好，但它是一个没有记录的功能，所以我不能再在iPhone OS4上使用它了。
所以…调整UIImage大小最简单的方法是什么?
当前回答
斯威夫特5:
func imageWithImage(_ image: UIImage?, scaledToSize newSize: CGSize) -> UIImage? {
UIGraphicsBeginImageContextWithOptions(newSize, false, 0.0);
image?.draw(in: CGRect(x: 0.0, y: 0.0, width: newSize.width, height: newSize.height))
let newImage: UIImage? = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return newImage
}
用法:
let img: UIImage? = imageWithImage(UIImage(named: "DefaultAvatar"), scaledToSize:CGSize(width: 20.0, height: 20.0))
其他回答
以下是斯威夫特版的保罗·林奇的回答
func imageWithImage(image:UIImage, scaledToSize newSize:CGSize) -> UIImage{
UIGraphicsBeginImageContextWithOptions(newSize, false, 0.0);
image.drawInRect(CGRectMake(0, 0, newSize.width, newSize.height))
let newImage:UIImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return newImage
}
作为延伸:
public extension UIImage {
func copy(newSize: CGSize, retina: Bool = true) -> UIImage? {
// In next line, pass 0 to use the current device's pixel scaling factor (and thus account for Retina resolution).
// Pass 1 to force exact pixel size.
UIGraphicsBeginImageContextWithOptions(
/* size: */ newSize,
/* opaque: */ false,
/* scale: */ retina ? 0 : 1
)
defer { UIGraphicsEndImageContext() }
self.draw(in: CGRect(origin: .zero, size: newSize))
return UIGraphicsGetImageFromCurrentImageContext()
}
}
为什么这么复杂?我认为使用系统API可以达到同样的效果:
UIImage *largeImage;
CGFloat ratio = 0.4; // you want to get a new image that is 40% the size of large image.
UIImage *newImage = [UIImage imageWithCGImage:largeImage.CGImage
scale:1/ratio
orientation:largeImage.imageOrientation];
// notice the second argument, it is 1/ratio, not ratio.
唯一的问题是你应该传递目标比率的倒数作为第二个参数，因为根据文档，第二个参数指定原始图像与新缩放图像的比率。
下面是iwasrob对上述类别的修改。它保持原始图像的纵横比，而不是扭曲它。
- (UIImage*)scaleToSizeKeepAspect:(CGSize)size {
UIGraphicsBeginImageContext(size);
CGFloat ws = size.width/self.size.width;
CGFloat hs = size.height/self.size.height;
if (ws > hs) {
ws = hs/ws;
hs = 1.0;
} else {
hs = ws/hs;
ws = 1.0;
}
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, 0.0, size.height);
CGContextScaleCTM(context, 1.0, -1.0);
CGContextDrawImage(context, CGRectMake(size.width/2-(size.width*ws)/2,
size.height/2-(size.height*hs)/2, size.width*ws,
size.height*hs), self.CGImage);
UIImage* scaledImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return scaledImage;
}
如果你只想要一个更小的图像，不关心确切的大小:
+ (UIImage *)imageWithImage:(UIImage *)image scaledToScale:(CGFloat)scale
{
UIGraphicsBeginImageContextWithOptions(self.size, YES, scale);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
[self drawInRect:CGRectMake(0, 0, self.size.width, self.size.height)];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
将比例设置为0.25f将从800万相机中获得816 * 612的图像。
这里有一个UIImage+Scale的分类。
斯威夫特5:
func imageWithImage(_ image: UIImage?, scaledToSize newSize: CGSize) -> UIImage? {
UIGraphicsBeginImageContextWithOptions(newSize, false, 0.0);
image?.draw(in: CGRect(x: 0.0, y: 0.0, width: newSize.width, height: newSize.height))
let newImage: UIImage? = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return newImage
}
用法:
let img: UIImage? = imageWithImage(UIImage(named: "DefaultAvatar"), scaledToSize:CGSize(width: 20.0, height: 20.0))
