我有一些代码可以调整图像的大小，这样我就可以得到图像中心的一定比例的块-我用它取a UIImage并返回图像的小正方形表示，类似于在的相册视图中看到的照片应用程序。（我知道我可以使用UIImageView和调整裁切模式来获得相同的结果，但是有时这些图像会显示在中UIWebViews）。

我已经开始注意到这段代码中的某些崩溃，我有些困惑。我有两种不同的理论，我想知道两者中的任何一种都没有。

理论1）我通过绘制到目标尺寸的屏幕外图像上下文来实现裁剪。由于我需要图像的中心部分，因此将CGRect传递的参数设置为drawInRect大于图像上下文边界的参数。我本以为这是犹太洁食，但我是不是想利用我不应该碰到的其他记忆？

理论2）我正在后台线程中完成所有这些工作。我知道UIKit的某些部分仅限于主线程。我以为/希望绘制到屏幕外的视图不是其中之一。我错了吗？

（哦，我怎么想念NSImage's drawInRect:fromRect:operation:fraction:方法。）

2014年5月28日更新：我在iOS 3左右是新事物时写了这篇文章，我敢肯定，目前有更好的方法可以做到这一点，可能是内置的。正如许多人提到的，这种方法没有考虑轮换。阅读一些其他答案，并散布一些赞美之词，以使对此问题的回答对每个人都有用。

原始回复：

我将在其他地方复制/粘贴对相同问题的回答：

没有简单的类方法可以执行此操作，但是可以使用一个函数来获得所需的结果：CGImageCreateWithImageInRect(CGImageRef, CGRect)将为您提供帮助。

这是一个使用它的简短示例：

CGImageRef imageRef = CGImageCreateWithImageInRect([largeImage CGImage], cropRect);
// or use the UIImage wherever you like
[UIImageView setImage:[UIImage imageWithCGImage:imageRef]]; 
CGImageRelease(imageRef);

要在保持相同比例和方向的同时裁剪视网膜图像，请在UIImage类别（iOS 4.0及更高版本）中使用以下方法：

- (UIImage *)crop:(CGRect)rect {
    if (self.scale > 1.0f) {
        rect = CGRectMake(rect.origin.x * self.scale,
                          rect.origin.y * self.scale,
                          rect.size.width * self.scale,
                          rect.size.height * self.scale);
    }

    CGImageRef imageRef = CGImageCreateWithImageInRect(self.CGImage, rect);
    UIImage *result = [UIImage imageWithCGImage:imageRef scale:self.scale orientation:self.imageOrientation];
    CGImageRelease(imageRef);
    return result;
}

您可以创建UIImage类别，并在需要的地方使用它。基于HitScans的响应和评论。

@implementation UIImage (Crop)

- (UIImage *)crop:(CGRect)rect {

    rect = CGRectMake(rect.origin.x*self.scale, 
                      rect.origin.y*self.scale, 
                      rect.size.width*self.scale, 
                      rect.size.height*self.scale);       

    CGImageRef imageRef = CGImageCreateWithImageInRect([self CGImage], rect);
    UIImage *result = [UIImage imageWithCGImage:imageRef 
                                          scale:self.scale 
                                    orientation:self.imageOrientation]; 
    CGImageRelease(imageRef);
    return result;
}

@end

您可以通过以下方式使用它：

UIImage *imageToCrop = <yourImageToCrop>;
CGRect cropRect = <areaYouWantToCrop>;   

//for example
//CGRectMake(0, 40, 320, 100);

UIImage *croppedImage = [imageToCrop crop:cropRect];

Swift 3版本

func cropImage(imageToCrop:UIImage, toRect rect:CGRect) -> UIImage{
    
    let imageRef:CGImage = imageToCrop.cgImage!.cropping(to: rect)!
    let cropped:UIImage = UIImage(cgImage:imageRef)
    return cropped
}


let imageTop:UIImage  = UIImage(named:"one.jpg")! // add validation

借助此桥函数CGRectMake-> CGRect（此答案的信用由回答@rob mayoff）：

 func CGRectMake(_ x: CGFloat, _ y: CGFloat, _ width: CGFloat, _ height: CGFloat) -> CGRect {
    return CGRect(x: x, y: y, width: width, height: height)
}

用法是：

if var image:UIImage  = UIImage(named:"one.jpg"){
   let  croppedImage = cropImage(imageToCrop: image, toRect: CGRectMake(
        image.size.width/4,
        0,
        image.size.width/2,
        image.size.height)
    )
}

输出：

这是我的UIImage裁剪实现，它遵循imageOrientation属性。所有方向都经过彻底测试。

inline double rad(double deg)
{
    return deg / 180.0 * M_PI;
}

UIImage* UIImageCrop(UIImage* img, CGRect rect)
{
    CGAffineTransform rectTransform;
    switch (img.imageOrientation)
    {
        case UIImageOrientationLeft:
            rectTransform = CGAffineTransformTranslate(CGAffineTransformMakeRotation(rad(90)), 0, -img.size.height);
            break;
        case UIImageOrientationRight:
            rectTransform = CGAffineTransformTranslate(CGAffineTransformMakeRotation(rad(-90)), -img.size.width, 0);
            break;
        case UIImageOrientationDown:
            rectTransform = CGAffineTransformTranslate(CGAffineTransformMakeRotation(rad(-180)), -img.size.width, -img.size.height);
            break;
        default:
            rectTransform = CGAffineTransformIdentity;
    };
    rectTransform = CGAffineTransformScale(rectTransform, img.scale, img.scale);

    CGImageRef imageRef = CGImageCreateWithImageInRect([img CGImage], CGRectApplyAffineTransform(rect, rectTransform));
    UIImage *result = [UIImage imageWithCGImage:imageRef scale:img.scale orientation:img.imageOrientation];
    CGImageRelease(imageRef);
    return result;
}

抬头：所有这些答案都假设一个CGImage支持图像的对象。

image.CGImage如果UIImage是以a为后缀，则可以返回nil，如果CIImage使用来创建此图片，则可能会返回nil CIFilter。

在这种情况下，您可能必须在新的上下文中绘制图像，然后返回该图像（slow）。

UIImage* crop(UIImage *image, rect) {
    UIGraphicsBeginImageContextWithOptions(rect.size, false, [image scale]);
    [image drawAtPoint:CGPointMake(-rect.origin.x, -rect.origin.y)];
    cropped_image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return cropped_image;
}

此处没有答案能正确处理所有比例和旋转问题。这是到目前为止所有内容的综合，是iOS7 / 8以来的最新信息。它应作为方法包含在UIImage的类别中。

- (UIImage *)croppedImageInRect:(CGRect)rect
{
    double (^rad)(double) = ^(double deg) {
        return deg / 180.0 * M_PI;
    };

    CGAffineTransform rectTransform;
    switch (self.imageOrientation) {
        case UIImageOrientationLeft:
            rectTransform = CGAffineTransformTranslate(CGAffineTransformMakeRotation(rad(90)), 0, -self.size.height);
            break;
        case UIImageOrientationRight:
            rectTransform = CGAffineTransformTranslate(CGAffineTransformMakeRotation(rad(-90)), -self.size.width, 0);
            break;
        case UIImageOrientationDown:
            rectTransform = CGAffineTransformTranslate(CGAffineTransformMakeRotation(rad(-180)), -self.size.width, -self.size.height);
            break;
        default:
            rectTransform = CGAffineTransformIdentity;
    };
    rectTransform = CGAffineTransformScale(rectTransform, self.scale, self.scale);

    CGImageRef imageRef = CGImageCreateWithImageInRect([self CGImage], CGRectApplyAffineTransform(rect, rectTransform));
    UIImage *result = [UIImage imageWithCGImage:imageRef scale:self.scale orientation:self.imageOrientation];
    CGImageRelease(imageRef);

    return result;
}

awolf的答案的Swift版本，对我有用：

public extension UIImage {
    func croppedImage(inRect rect: CGRect) -> UIImage {
        let rad: (Double) -> CGFloat = { deg in
            return CGFloat(deg / 180.0 * .pi)
        }
        var rectTransform: CGAffineTransform
        switch imageOrientation {
        case .left:
            let rotation = CGAffineTransform(rotationAngle: rad(90))
            rectTransform = rotation.translatedBy(x: 0, y: -size.height)
        case .right:
            let rotation = CGAffineTransform(rotationAngle: rad(-90))
            rectTransform = rotation.translatedBy(x: -size.width, y: 0)
        case .down:
            let rotation = CGAffineTransform(rotationAngle: rad(-180))
            rectTransform = rotation.translatedBy(x: -size.width, y: -size.height)
        default:
            rectTransform = .identity
        }
        rectTransform = rectTransform.scaledBy(x: scale, y: scale)
        let transformedRect = rect.applying(rectTransform)
        let imageRef = cgImage!.cropping(to: transformedRect)!
        let result = UIImage(cgImage: imageRef, scale: scale, orientation: imageOrientation)
        return result
    }
}

CGSize size = [originalImage size];
int padding = 20;
int pictureSize = 300;
int startCroppingPosition = 100;
if (size.height > size.width) {
    pictureSize = size.width - (2.0 * padding);
    startCroppingPosition = (size.height - pictureSize) / 2.0; 
} else {
    pictureSize = size.height - (2.0 * padding);
    startCroppingPosition = (size.width - pictureSize) / 2.0;
}
// WTF: Don't forget that the CGImageCreateWithImageInRect believes that 
// the image is 180 rotated, so x and y are inverted, same for height and width.
CGRect cropRect = CGRectMake(startCroppingPosition, padding, pictureSize, pictureSize);
CGImageRef imageRef = CGImageCreateWithImageInRect([originalImage CGImage], cropRect);
UIImage *newImage = [UIImage imageWithCGImage:imageRef scale:1.0 orientation:originalImage.imageOrientation];
[m_photoView setImage:newImage];
CGImageRelease(imageRef);

我见过的大多数回复仅针对（x，y）处理（0，0）的位置。好的，这是一种情况，但我希望将裁切操作居中。我花了一段时间才弄清楚了WTF评论之后的内容。

让我们以纵向拍摄的图像为例：

1. 原始图像的高度高于其宽度（哦，到目前为止，还不足为奇！）
2. CGImageCreateWithImageInRect方法在自己的世界中想象的图像虽然不是真正的人像，但是却是风景（这就是为什么如果不在imageWithCGImage构造函数中使用direction参数，它将显示为180度旋转）。
3. 因此，您应该想象一下它是风景，（0，0）位置是图像的右上角。

希望有道理！如果没有，请尝试不同的值，当您为cropRect选择正确的x，y，宽度和高度时，您会发现逻辑是相反的。

迅捷3

extension UIImage {
    func crop(rect: CGRect) -> UIImage? {
        var scaledRect = rect
        scaledRect.origin.x *= scale
        scaledRect.origin.y *= scale
        scaledRect.size.width *= scale
        scaledRect.size.height *= scale
        guard let imageRef: CGImage = cgImage?.cropping(to: scaledRect) else {
            return nil
        }
        return UIImage(cgImage: imageRef, scale: scale, orientation: imageOrientation)
    }
}

迅速扩展

extension UIImage {
    func crop(var rect: CGRect) -> UIImage {
        rect.origin.x*=self.scale
        rect.origin.y*=self.scale
        rect.size.width*=self.scale
        rect.size.height*=self.scale

        let imageRef = CGImageCreateWithImageInRect(self.CGImage, rect)
        let image = UIImage(CGImage: imageRef, scale: self.scale, orientation: self.imageOrientation)!
        return image
    }
}

就精度，像素缩放...而言，在Swift中裁剪UIImage的最佳解决方案：

private func squareCropImageToSideLength(let sourceImage: UIImage,
    let sideLength: CGFloat) -> UIImage {
        // input size comes from image
        let inputSize: CGSize = sourceImage.size

        // round up side length to avoid fractional output size
        let sideLength: CGFloat = ceil(sideLength)

        // output size has sideLength for both dimensions
        let outputSize: CGSize = CGSizeMake(sideLength, sideLength)

        // calculate scale so that smaller dimension fits sideLength
        let scale: CGFloat = max(sideLength / inputSize.width,
            sideLength / inputSize.height)

        // scaling the image with this scale results in this output size
        let scaledInputSize: CGSize = CGSizeMake(inputSize.width * scale,
            inputSize.height * scale)

        // determine point in center of "canvas"
        let center: CGPoint = CGPointMake(outputSize.width/2.0,
            outputSize.height/2.0)

        // calculate drawing rect relative to output Size
        let outputRect: CGRect = CGRectMake(center.x - scaledInputSize.width/2.0,
            center.y - scaledInputSize.height/2.0,
            scaledInputSize.width,
            scaledInputSize.height)

        // begin a new bitmap context, scale 0 takes display scale
        UIGraphicsBeginImageContextWithOptions(outputSize, true, 0)

        // optional: set the interpolation quality.
        // For this you need to grab the underlying CGContext
        let ctx: CGContextRef = UIGraphicsGetCurrentContext()
        CGContextSetInterpolationQuality(ctx, kCGInterpolationHigh)

        // draw the source image into the calculated rect
        sourceImage.drawInRect(outputRect)

        // create new image from bitmap context
        let outImage: UIImage = UIGraphicsGetImageFromCurrentImageContext()

        // clean up
        UIGraphicsEndImageContext()

        // pass back new image
        return outImage
}

用于调用此函数的说明：

let image: UIImage = UIImage(named: "Image.jpg")!
let squareImage: UIImage = self.squareCropImageToSideLength(image, sideLength: 320)
self.myUIImageView.image = squareImage

注意：在“ Cocoanetics”博客上可以找到用Objective-C编写的初始源代码。

下面的代码段可能会有所帮助。

import UIKit

extension UIImage {
    func cropImage(toRect rect: CGRect) -> UIImage? {
        if let imageRef = self.cgImage?.cropping(to: rect) {
            return UIImage(cgImage: imageRef)
        }
        return nil
    }
}

看起来有些奇怪，但效果很好，并考虑了图像方向：

var image:UIImage = ...

let img = CIImage(image: image)!.imageByCroppingToRect(rect)
image = UIImage(CIImage: img, scale: 1, orientation: image.imageOrientation)

斯威夫特5：

extension UIImage {
    func cropped(rect: CGRect) -> UIImage? {
        guard let cgImage = cgImage else { return nil }

        UIGraphicsBeginImageContextWithOptions(rect.size, false, 0)
        let context = UIGraphicsGetCurrentContext()

        context?.translateBy(x: 0.0, y: self.size.height)
        context?.scaleBy(x: 1.0, y: -1.0)
        context?.draw(cgImage, in: CGRect(x: rect.minX, y: rect.minY, width: self.size.width, height: self.size.height), byTiling: false)


        let croppedImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return croppedImage
    }
}

- (UIImage *)getSubImage:(CGRect) rect{
    CGImageRef subImageRef = CGImageCreateWithImageInRect(self.CGImage, rect);
    CGRect smallBounds = CGRectMake(rect.origin.x, rect.origin.y, CGImageGetWidth(subImageRef), CGImageGetHeight(subImageRef));

    UIGraphicsBeginImageContext(smallBounds.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextDrawImage(context, smallBounds, subImageRef);
    UIImage* smallImg = [UIImage imageWithCGImage:subImageRef];
    UIGraphicsEndImageContext();

    return smallImg;
}

 (UIImage *)squareImageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize {
    double ratio;
    double delta;
    CGPoint offset;

    //make a new square size, that is the resized imaged width
    CGSize sz = CGSizeMake(newSize.width, newSize.width);

    //figure out if the picture is landscape or portrait, then
    //calculate scale factor and offset
    if (image.size.width > image.size.height) {
        ratio = newSize.width / image.size.width;
        delta = (ratio*image.size.width - ratio*image.size.height);
        offset = CGPointMake(delta/2, 0);
    } else {
        ratio = newSize.width / image.size.height;
        delta = (ratio*image.size.height - ratio*image.size.width);
        offset = CGPointMake(0, delta/2);
    }

    //make the final clipping rect based on the calculated values
    CGRect clipRect = CGRectMake(-offset.x, -offset.y,
                                 (ratio * image.size.width) + delta,
                                 (ratio * image.size.height) + delta);


    //start a new context, with scale factor 0.0 so retina displays get
    //high quality image
    if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)]) {
        UIGraphicsBeginImageContextWithOptions(sz, YES, 0.0);
    } else {
        UIGraphicsBeginImageContext(sz);
    }
    UIRectClip(clipRect);
    [image drawInRect:clipRect];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return newImage;
}

在iOS9.2SDK上，我使用以下方法将帧从UIView转换为UIImage

-(UIImage *)getNeedImageFrom:(UIImage*)image cropRect:(CGRect)rect
{
  CGSize cropSize = rect.size;
  CGFloat widthScale = image.size.width/self.imageViewOriginal.bounds.size.width;
  CGFloat heightScale = image.size.height/self.imageViewOriginal.bounds.size.height;
  cropSize = CGSizeMake(rect.size.width*widthScale, 
              rect.size.height*heightScale);
  CGPoint pointCrop = CGPointMake(rect.origin.x*widthScale,
             rect.origin.y*heightScale);
  rect = CGRectMake(pointCrop.x, pointCrop.y, cropSize.width, cropSize.height);
  CGImageRef subImage = CGImageCreateWithImageInRect(image.CGImage, rect);
  UIImage *croppedImage = [UIImage imageWithCGImage:subImage];
  CGImageRelease(subImage);

  return croppedImage;
}

Swift 2.0更新（CIImage兼容性）

扩展Maxim's Answer，但也可以在您的图像CIImage基于的情况下使用。

public extension UIImage {
    func imageByCroppingToRect(rect: CGRect) -> UIImage? {
        if let image = CGImageCreateWithImageInRect(self.CGImage, rect) {
            return UIImage(CGImage: image)
        } else if let image = (self.CIImage)?.imageByCroppingToRect(rect) {
            return UIImage(CIImage: image)
        }
       return nil
   }
}

这是基于Noodles答案的更新的Swift 3版本

func cropping(to rect: CGRect) -> UIImage? {

    if let cgCrop = cgImage?.cropping(to: rect) {
        return UIImage(cgImage: cgCrop)
    }
    else if let ciCrop = ciImage?.cropping(to: rect) {
        return UIImage(ciImage: ciCrop)
    }

    return nil
}

关注@Arne的答案。我只是固定到类别功能。将其放在UIImage的类别中。

-(UIImage*)cropImage:(CGRect)rect{

    UIGraphicsBeginImageContextWithOptions(rect.size, false, [self scale]);
    [self drawAtPoint:CGPointMake(-rect.origin.x, -rect.origin.y)];
    UIImage* cropped_image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return cropped_image;
}

我对其他解决方案不满意，因为它们要么花了很多时间（使用了比必要的功率更多的功率），要么出现了方向问题。这是我用于从UIImage *图像缩放的正方形croppedImage的内容。

CGFloat minimumSide = fminf(image.size.width, image.size.height);
CGFloat finalSquareSize = 600.;

//create new drawing context for right size
CGRect rect = CGRectMake(0, 0, finalSquareSize, finalSquareSize);
CGFloat scalingRatio = 640.0/minimumSide;
UIGraphicsBeginImageContext(rect.size);

//draw
[image drawInRect:CGRectMake((minimumSide - photo.size.width)*scalingRatio/2., (minimumSide - photo.size.height)*scalingRatio/2., photo.size.width*scalingRatio, photo.size.height*scalingRatio)];

UIImage *croppedImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

我使用下面的方法。

  -(UIImage *)getNeedImageFrom:(UIImage*)image cropRect:(CGRect)rect
  {
    CGSize cropSize = rect.size;
    CGFloat widthScale =  
    image.size.width/self.imageViewOriginal.bounds.size.width;
    CGFloat heightScale = 
    image.size.height/self.imageViewOriginal.bounds.size.height;
    cropSize = CGSizeMake(rect.size.width*widthScale,  
    rect.size.height*heightScale);
    CGPoint  pointCrop = CGPointMake(rect.origin.x*widthScale, 
    rect.origin.y*heightScale);
    rect = CGRectMake(pointCrop.x, pointCrop.y, cropSize.width, 
    cropSize.height);
    CGImageRef subImage = CGImageCreateWithImageInRect(image.CGImage, rect);
    UIImage *croppedImage = [UIImage imageWithCGImage:subImage];
    CGImageRelease(subImage);
    return croppedImage;

}

看看https://github.com/vvbogdan/BVCropPhoto

-（UIImage *）croppedImage {
    CGFloat比例= self.sourceImage.size.width / self.scrollView.contentSize.width;

    UIImage * finalImage = nil;
    CGRect targetFrame = CGRectMake（（self.scrollView.contentInset.left + self.scrollView.contentOffset.x）*比例尺，
            （self.scrollView.contentInset.top + self.scrollView.contentOffset.y）*比例尺，
            self.cropSize.width *比例尺，
            self.cropSize.height *比例）；

    CGImageRef contextImage = CGImageCreateWithImageInRect（[[[self imageWithRotation：self.sourceImage] CGImage]，targetFrame）;

    如果（contextImage！= NULL）{
        finalImage = [UIImage imageWithCGImage：contextImage
                                         规模：self.sourceImage.scale
                                   方向：UIImageOrientationUp];

        CGImageRelease（contextImage）;
    }

    返回finalImage;
}


-（UIImage *）imageWithRotation：（UIImage *）image {


    如果（image.imageOrientation == UIImageOrientationUp）返回图像；
    CGAffineTransform transform = CGAffineTransformIdentity;

    开关（image.imageOrientation）{
        案例UIImageOrientationDown：
        案例UIImageOrientationDownMirrored：
            transform = CGAffineTransformTranslate（transform，image.size.width，image.size.height）;
            转换= CGAffineTransformRotate（transform，M_PI）;
            打破;

        案例UIImageOrientationLeft：
        案例UIImageOrientationLeftMirrored：
            transform = CGAffineTransformTranslate（transform，image.size.width，0）;
            转换= CGAffineTransformRotate（transform，M_PI_2）;
            打破;

        案例UIImageOrientationRight：
        案例UIImageOrientationRightMirrored：
            transform = CGAffineTransformTranslate（transform，0，image.size.height）;
            转换= CGAffineTransformRotate（transform，-M_PI_2）;
            打破;
        案例UIImageOrientationUp：
        案例UIImageOrientationUpMirrored：
            打破;
    }

    开关（image.imageOrientation）{
        案例UIImageOrientationUpMirrored：
        案例UIImageOrientationDownMirrored：
            transform = CGAffineTransformTranslate（transform，image.size.width，0）;
            transform = CGAffineTransformScale（transform，-1，1）;
            打破;

        案例UIImageOrientationLeftMirrored：
        案例UIImageOrientationRightMirrored：
            transform = CGAffineTransformTranslate（transform，image.size.height，0）;
            transform = CGAffineTransformScale（transform，-1，1）;
            打破;
        案例UIImageOrientationUp：
        案例UIImageOrientationDown：
        案例UIImageOrientationLeft：
        案例UIImageOrientationRight：
            打破;
    }

    //现在，应用转换将基础CGImage绘制到新的上下文中
    //以上计算得出。
    CGContextRef ctx = CGBitmapContextCreate（NULL，image.size.width，image.size.height，
            CGImageGetBitsPerComponent（image.CGImage），0，
            CGImageGetColorSpace（image.CGImage），
            CGImageGetBitmapInfo（image.CGImage））;
    CGContextConcatCTM（ctx，transform）;
    开关（image.imageOrientation）{
        案例UIImageOrientationLeft：
        案例UIImageOrientationLeftMirrored：
        案例UIImageOrientationRight：
        案例UIImageOrientationRightMirrored：
            // Grr ...
            CGContextDrawImage（ctx，CGRectMake（0，0，image.size.height，image.size.width），image.CGImage）;
            打破;

        默认：
            CGContextDrawImage（ctx，CGRectMake（0，0，image.size.width，image.size.height），image.CGImage）;
            打破;
    }

    //现在，我们只需根据绘图上下文创建一个新的UIImage
    CGImageRef cgimg = CGBitmapContextCreateImage（ctx）;
    UIImage * img = [UIImage imageWithCGImage：cgimg];
    CGContextRelease（ctx）;
    CGImageRelease（cgimg）;
    返回img;

}