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

快速解决方案的拉伸填充,方面填补和方面适合

extension UIImage {
    enum ContentMode {
        case contentFill
        case contentAspectFill
        case contentAspectFit
    }
    
    func resize(withSize size: CGSize, contentMode: ContentMode = .contentAspectFill) -> UIImage? {
        let aspectWidth = size.width / self.size.width
        let aspectHeight = size.height / self.size.height
        
        switch contentMode {
        case .contentFill:
            return resize(withSize: size)
        case .contentAspectFit:
            let aspectRatio = min(aspectWidth, aspectHeight)
            return resize(withSize: CGSize(width: self.size.width * aspectRatio, height: self.size.height * aspectRatio))
        case .contentAspectFill:
            let aspectRatio = max(aspectWidth, aspectHeight)
            return resize(withSize: CGSize(width: self.size.width * aspectRatio, height: self.size.height * aspectRatio))
        }
    }
    
    private func resize(withSize size: CGSize) -> UIImage? {
        UIGraphicsBeginImageContextWithOptions(size, false, self.scale)
        defer { UIGraphicsEndImageContext() }
        draw(in: CGRect(x: 0.0, y: 0.0, width: size.width, height: size.height))
        return UIGraphicsGetImageFromCurrentImageContext()
    }
}

要使用,您可以执行以下操作:

let image = UIImage(named: "image.png")!
let newImage = image.resize(withSize: CGSize(width: 200, height: 150), contentMode: .contentAspectFill)

感谢abdullahselek最初的解决方案。

其他回答

如果你想做一个UIImage的缩略图(按比例调整大小或可能涉及到一些裁剪),检查UIImage+Resize类别,它允许你使用简洁的,类似imagemagick的语法:

UIImage* squareImage       = [image resizedImageByMagick: @"320x320#"];

[cf Chris]调整大小到所需的大小:

UIImage *after = [UIImage imageWithCGImage:before.CGImage
                                     scale:CGImageGetHeight(before.CGImage)/DESIREDHEIGHT
                               orientation:UIImageOrientationUp];

或者,等效地,替换CGImageGetWidth(…)/DESIREDWIDTH

最简单的方法是设置UIImageView的框架,并将contentMode设置为其中一个调整大小的选项。

或者你可以使用这个实用工具方法,如果你真的需要调整图像的大小:

+ (UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize {
    //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.
    UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);
    [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();    
    UIGraphicsEndImageContext();
    return newImage;
}

使用示例:

#import "MYUtil.h"
…
UIImage *myIcon = [MYUtil imageWithImage:myUIImageInstance scaledToSize:CGSizeMake(20, 20)];

正确的Swift 3.0 iOS 10+解决方案:使用ImageRenderer和闭包语法:

func imageWith(newSize: CGSize) -> UIImage {
    let image = UIGraphicsImageRenderer(size: newSize).image { _ in
        draw(in: CGRect(origin: .zero, size: newSize))
    }
        
    return image.withRenderingMode(renderingMode)
}

这是Objective-C版本:

@implementation UIImage (ResizeCategory)
- (UIImage *)imageWithSize:(CGSize)newSize
{
    UIGraphicsImageRenderer *renderer = [[UIGraphicsImageRenderer alloc] initWithSize:newSize];
    UIImage *image = [renderer imageWithActions:^(UIGraphicsImageRendererContext*_Nonnull myContext) {
        [self drawInRect:(CGRect) {.origin = CGPointZero, .size = newSize}];
    }];
    return [image imageWithRenderingMode:self.renderingMode];
}
@end

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。