Question

我在很多文章中都看到过通过保持宽高比来调整图像大小。这些函数在调整大小时使用RECT的固定点（宽度和高度）。但是在我的项目中，我需要仅根据宽度调整视图大小，应根据宽高比自动获取高度。任何人帮助我实现这一目标。

Answer 1

如果您知道新尺寸的高度和宽度，Srikar的方法效果很好。例如，如果您只知道要缩放的宽度而不关心高度，则首先必须计算高度的比例因子。

+(UIImage*)imageWithImage: (UIImage*) sourceImage scaledToWidth: (float) i_width
{
    float oldWidth = sourceImage.size.width;
    float scaleFactor = i_width / oldWidth;

    float newHeight = sourceImage.size.height * scaleFactor;
    float newWidth = oldWidth * scaleFactor;

    UIGraphicsBeginImageContext(CGSizeMake(newWidth, newHeight));
    [sourceImage drawInRect:CGRectMake(0, 0, newWidth, newHeight)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();    
    UIGraphicsEndImageContext();
    return newImage;
}

Answer 2

如果您不知道图像是纵向还是横向（例如用户使用相机拍照），我创建了另一种采用最大宽度和高度参数的方法。

假设您有一个UIImage *myLargeImage比例为4：3。

UIImage *myResizedImage = [ImageUtilities imageWithImage:myLargeImage 
                                        scaledToMaxWidth:1024 
                                               maxHeight:1024];

如果是风景，重新调整大小的UIImage将是1024x768; 768x1024如果肖像。此方法还将为视网膜显示生成更高分辨率的图像。

+ (UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)size {
    if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)]) {
        UIGraphicsBeginImageContextWithOptions(size, NO, [[UIScreen mainScreen] scale]);
    } else {
        UIGraphicsBeginImageContext(size);
    }
    [image drawInRect:CGRectMake(0, 0, size.width, size.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();    
    UIGraphicsEndImageContext();

    return newImage;
}

+ (UIImage *)imageWithImage:(UIImage *)image scaledToMaxWidth:(CGFloat)width maxHeight:(CGFloat)height {
    CGFloat oldWidth = image.size.width;
    CGFloat oldHeight = image.size.height;

    CGFloat scaleFactor = (oldWidth > oldHeight) ? width / oldWidth : height / oldHeight;

    CGFloat newHeight = oldHeight * scaleFactor;
    CGFloat newWidth = oldWidth * scaleFactor;
    CGSize newSize = CGSizeMake(newWidth, newHeight);

    return [ImageUtilities imageWithImage:image scaledToSize:newSize];
}

Answer 3

最佳答案Maverick 1st正确翻译为 Swift （使用最新的 swift 3 ）：

func imageWithImage (sourceImage:UIImage, scaledToWidth: CGFloat) -> UIImage {
    let oldWidth = sourceImage.size.width
    let scaleFactor = scaledToWidth / oldWidth

    let newHeight = sourceImage.size.height * scaleFactor
    let newWidth = oldWidth * scaleFactor

    UIGraphicsBeginImageContext(CGSize(width:newWidth, height:newHeight))
    sourceImage.draw(in: CGRect(x:0, y:0, width:newWidth, height:newHeight))
    let newImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return newImage!
}

Answer 4

感谢@ Maverick1st算法，我将其实现为 Swift ，在我的情况下，height是输入参数

class func resizeImage(image: UIImage, newHeight: CGFloat) -> UIImage {

    let scale = newHeight / image.size.height
    let newWidth = image.size.width * scale
    UIGraphicsBeginImageContext(CGSizeMake(newWidth, newHeight))
    image.drawInRect(CGRectMake(0, 0, newWidth, newHeight))
    let newImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return newImage
}

Answer 5

此方法是UIImage上的一个类别。使用AVFoundation缩放以适应几行代码。不要忘记导入#import <AVFoundation/AVFoundation.h>。

@implementation UIImage (Helper)

- (UIImage *)imageScaledToFitToSize:(CGSize)size
{
    CGRect scaledRect = AVMakeRectWithAspectRatioInsideRect(self.size, CGRectMake(0, 0, size.width, size.height));
    UIGraphicsBeginImageContextWithOptions(size, NO, 0);
    [self drawInRect:scaledRect];
    UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return scaledImage;
}

@end

Answer 6

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选项。

代码是这样的 - 这可以用作实用方法 -

+ (UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize
{
    UIGraphicsBeginImageContext(newSize);
    [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();    
    UIGraphicsEndImageContext();
    return newImage;
}

Answer 7

嗯，我们这里没有很好的答案来调整图像大小，但我只是根据需要进行修改。希望这能帮到像我这样的人。

我的要求是

如果图像宽度大于1920，请使用1920宽度调整大小，并使用原始高宽比保持高度。
如果图像高度超过1080，请使用1080高度调整大小并使用原始高宽比保持宽度。

 if (originalImage.size.width > 1920)
 {
        CGSize newSize;
        newSize.width = 1920;
        newSize.height = (1920 * originalImage.size.height) / originalImage.size.width;
        originalImage = [ProfileEditExperienceViewController imageWithImage:originalImage scaledToSize:newSize];        
 }

 if (originalImage.size.height > 1080)
 {
            CGSize newSize;
            newSize.width = (1080 * originalImage.size.width) / originalImage.size.height;
            newSize.height = 1080;
            originalImage = [ProfileEditExperienceViewController imageWithImage:originalImage scaledToSize:newSize];

 }

+ (UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize
{
        UIGraphicsBeginImageContext(newSize);
        [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
        UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        return newImage;
}

感谢@ Srikar Appal，为了调整大小，我使用了他的方法。

您可以查看this以及调整大小计算。

Answer 8

编程：

imageView.contentMode = UIViewContentModeScaleAspectFit;

故事板：

Answer 9

只需导入AVFoundation并使用AVMakeRectWithAspectRatioInsideRect(CGRectCurrentSize, CGRectMake(0, 0, YOUR_WIDTH, CGFLOAT_MAX)

Answer 10

改进Ryan的回答：

   + (UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)size {
CGFloat oldWidth = image.size.width;
        CGFloat oldHeight = image.size.height;

//You may need to take some retina adjustments into consideration here
        CGFloat scaleFactor = (oldWidth > oldHeight) ? width / oldWidth : height / oldHeight;

return [UIImage imageWithCGImage:image.CGImage scale:scaleFactor orientation:UIImageOrientationUp];
    }

Answer 11

Ryan的解决方案@Ryan 在快速代码中

使用：

while (infile >> s >> a[0] >> a[1] >> a[2]) {
    ...
}

Answer 12

在 Swift 3 中有一些变化。这是UIImage的扩展：

public extension UIImage {
    public func resize(height: CGFloat) -> UIImage? {
        let scale = height / self.size.height
        let width = self.size.width * scale
        UIGraphicsBeginImageContext(CGSize(width: width, height: height))
        self.draw(in: CGRect(x:0, y:0, width:width, height:height))
        let resultImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return resultImage
    }
}

Answer 13

extension UIImage {

    /// Returns a image that fills in newSize
    func resizedImage(newSize: CGSize) -> UIImage? {
        guard size != newSize else { return self }

    let hasAlpha = false
    let scale: CGFloat = 0.0
    UIGraphicsBeginImageContextWithOptions(newSize, !hasAlpha, scale)
        UIGraphicsBeginImageContextWithOptions(newSize, false, 0.0)

        draw(in: CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height))
        let newImage: UIImage? = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return newImage
    }

    /// Returns a resized image that fits in rectSize, keeping it's aspect ratio
    /// Note that the new image size is not rectSize, but within it.
    func resizedImageWithinRect(rectSize: CGSize) -> UIImage? {
        let widthFactor = size.width / rectSize.width
        let heightFactor = size.height / rectSize.height

        var resizeFactor = widthFactor
        if size.height > size.width {
            resizeFactor = heightFactor
        }

        let newSize = CGSize(width: size.width / resizeFactor, height: size.height / resizeFactor)
        let resized = resizedImage(newSize: newSize)

        return resized
    }
}

当比例设置为0.0时，将使用主屏幕的比例因子，对于Retina显示屏，该比例因子为2.0或更高（iPhone 6 Plus为3.0）。

Answer 14

如果有人在Swift 5中需要此解决方案：

private func resizeImage(image: UIImage, newHeight: CGFloat) -> UIImage {
    
    let scale = newHeight / image.size.height
    let newWidth = image.size.width * scale
    UIGraphicsBeginImageContext(CGSize(width:newWidth, height:newHeight))
    image.draw(in:CGRect(x:0, y:0, width:newWidth, height:newHeight))
    let newImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return newImage
}

Answer 15

Zeeshan Tufail和Womble在 Swift 5 中的答案有所改进。这里我们有2个功能扩展，可以将图像缩放到任意尺寸的maxLength并进行jpeg压缩。

extension UIImage {
func aspectFittedToMaxLengthData(maxLength: CGFloat, compressionQuality: CGFloat) -> Data {
    let scale = maxLength / max(self.size.height, self.size.width)
    let format = UIGraphicsImageRendererFormat()
    format.scale = scale
    let renderer = UIGraphicsImageRenderer(size: self.size, format: format)
    return renderer.jpegData(withCompressionQuality: compressionQuality) { context in
        self.draw(in: CGRect(origin: .zero, size: self.size))
    }
}
func aspectFittedToMaxLengthImage(maxLength: CGFloat, compressionQuality: CGFloat) -> UIImage? {
    let newImageData = aspectFittedToMaxLengthData(maxLength: maxLength, compressionQuality: compressionQuality)
    return UIImage(data: newImageData)
}

}

Answer 16

Swift 5 版本的宽高比高度，基于@János的回答

使用现代的UIGraphicsImageRenderer API，因此可以保证返回有效的UIImage。

extension UIImage
{
    /// Given a required height, returns a (rasterised) copy
    /// of the image, aspect-fitted to that height.

    func aspectFittedToHeight(_ newHeight: CGFloat) -> UIImage
    {
        let scale = newHeight / self.size.height
        let newWidth = self.size.width * scale
        let newSize = CGSize(width: newWidth, height: newHeight)
        let renderer = UIGraphicsImageRenderer(size: newSize)

        return renderer.image { _ in
            self.draw(in: CGRect(origin: .zero, size: newSize))
        }
    }
}

您可以将其与（基于矢量的）PDF图像资产结合使用，以保持任何渲染尺寸的质量。

Answer 17

计算可用宽度的图像最佳高度。

import Foundation

public extension UIImage {
    public func height(forWidth width: CGFloat) -> CGFloat {
        let boundingRect = CGRect(
            x: 0,
            y: 0,
            width: width,
            height: CGFloat(MAXFLOAT)
        )
        let rect = AVMakeRect(
            aspectRatio: size,
            insideRect: boundingRect
        )
        return rect.size.height
    }
}

Answer 18

这个对我来说很完美。保持宽高比并获得maxLength。宽度或高度不会超过maxLength

-(UIImage*)imageWithImage: (UIImage*) sourceImage maxLength: (float) maxLength
{
    CGFloat scaleFactor = maxLength / MAX(sourceImage.size.width, sourceImage.size.height);

    float newHeight = sourceImage.size.height * scaleFactor;
    float newWidth = sourceImage.size.width * scaleFactor;

    UIGraphicsBeginImageContext(CGSizeMake(newWidth, newHeight));
    [sourceImage drawInRect:CGRectMake(0, 0, newWidth, newHeight)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

Answer 19

我用更简单的方式解决了它

UIImage *placeholder = [UIImage imageNamed:@"OriginalImage.png"];
self.yourImageview.image = [UIImage imageWithCGImage:[placeholder CGImage] scale:(placeholder.scale * 1.5)
                                  orientation:(placeholder.imageOrientation)];

比例的乘数将定义图像的scalling，更多的乘数更小的图像。所以你可以检查一下你的屏幕是什么。

或者您也可以通过划分图像宽度/屏幕宽度来获得倍数。

通过保持宽高比和宽度来调整UIImage的大小

19 个答案: