通過保持縱橫比和寬度來調整 UIImage 的大小

Question

我在許多帖子中看到通過保持縱橫比來調整圖像大小。 這些函數在調整大小時使用 RECT 的固定點（寬度和高度）。 但是在我的項目中，我需要僅根據寬度調整視圖大小，應根據縱橫比自動獲取高度。 任何人都可以幫助我實現這一目標。

Answer 1

如果您知道新尺寸的高度和寬度，Srikar 的方法效果很好。 例如，如果您只知道要縮放到的寬度而不關心高度，則首先必須計算高度的比例因子。

+(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

如果您不知道圖像是縱向還是橫向（例如用戶用相機拍照），我創建了另一種采用最大寬度和高度參數的方法。

假設您有一個比例為 4:3 的UIImage *myLargeImage 。

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

如果是橫向，調整后的 UIImage 將為 1024x768； 768x1024 如果是縱向。 此方法還將為視網膜顯示生成更高分辨率的圖像。

+ (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 正確翻譯為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

感謝@Maverick1st 算法，我將它實現到Swift ，在我的情況下 height 是輸入參數

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

這個方法是 UIImage 上的一個類。 使用 AVFoundation 進行縮放以適應幾行代碼。 不要忘記導入#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

Swift 5版本的 aspect-fit-to- height ，基於@János 的回答

使用現代UIGraphicsImageRenderer API，因此保證返回有效的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))
        }
    }
}

您可以將它與（基於矢量的）PDF 圖像資產結合使用，以保持任何渲染尺寸的質量。

Answer 7

最簡單的方法是設置UIImageView的框架並將contentMode設置為調整大小選項之一。

代碼是這樣的 - 這可以用作實用方法 -

+ (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 8

好吧，我們在這里調整圖像大小的答案很少，但我只是根據我的需要進行修改。 希望這能幫助像我這樣的人。

我的要求是

1. 如果圖像寬度大於 1920，則將其調整為 1920 寬度並保持高度與原始縱橫比。
2. 如果圖像高度超過 1080，則將其調整為 1080 高度並保持寬度與原始縱橫比。

---

 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;
}

感謝@ Srikar Appal ，為了調整大小，我使用了他的方法。

您可能還想檢查這個以進行調整大小計算。

Answer 9

以編程方式：

imageView.contentMode = UIViewContentModeScaleAspectFit;

故事板：

Answer 10

只需導入 AVFoundation 並使用AVMakeRectWithAspectRatioInsideRect(CGRectCurrentSize, CGRectMake(0, 0, YOUR_WIDTH, CGFLOAT_MAX)

Answer 11

改進瑞安的回答：

   + (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 12

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
    }
}

當 scale 設置為 0.0 時，使用主屏幕的比例因子，對於 Retina 顯示器，該比例因子為 2.0 或更高（iPhone 6 Plus 為 3.0）。

Answer 13

Ryan 在 swift 代碼中的解決方案@Ryan

采用：

 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;
}

//Summon this function VVV
func resizeImageWithAspect(image: UIImage,scaledToMaxWidth width:CGFloat,maxHeight height :CGFloat)->UIImage
{
    let oldWidth = image.size.width;
    let oldHeight = image.size.height;

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

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

    return imageWithSize(image, size: newSize);
}

Answer 14

在Swift 3 中有一些變化。 這是 UIImage 的擴展：

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 15

計算可用寬度的圖像的最佳高度。

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 16

Zeeshan Tufail 和 Womble 在Swift 5 中回答了一些小改進。 這里我們有 2 個函數的擴展，可以將圖像縮放到任何維度的maxLength和 jpeg 壓縮。

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 17

如果有人在 Swift 5 中需要這個解決方案：

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 18

這個對我來說是完美的。 保持縱橫比並采用maxLength 。 寬度或高度不會超過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

我用更簡單的方式解決了它

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

比例的乘數將定義圖像的縮放，乘數越大圖像越小。 所以你可以檢查什么適合你的屏幕。

或者您也可以通過除以圖像寬度/屏幕寬度來獲得乘數。