我有一些代码可以调整图像的大小，因此我可以获得图像中心的缩放块 - 我使用它来获取UIImage并返回图像的一个小的方形表示，类似于在专辑视图中看到的照片应用程序。（我知道我可以使用 aUIImageView并调整裁剪模式来获得相同的结果，但这些图像有时会显示在 中UIWebViews）。
我开始注意到这段代码中有一些崩溃，我有点难过。我有两种不同的理论，我想知道是否有任何一种是基于的。
理论 1）我通过绘制到我的目标尺寸的屏幕外图像上下文来实现裁剪。由于我想要图像的中心部分，因此我将CGRect传递给的参数设置为drawInRect大于图像上下文范围的参数。我希望这是 Kosher，但我是不是试图画出我不应该接触的其他记忆？
理论2）我在后台线程中完成所有这些。我知道 UIKit 的某些部分仅限于主线程。我假设/希望绘制到屏幕外视图不是其中之一。我错了吗？
（哦，我多么怀念NSImage's drawInRect:fromRect:operation:fraction:方法。）
2014-05-28 更新：我在 iOS 3 左右是热门新事物时写了这个，我敢肯定现在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；阅读一些额外的答案并传播一些赞成的爱，以使对这个问题的回答对每个人都有帮助。
原始回复：
我将在别处复制/粘贴我对同一问题的回答：
没有一个简单的类方法可以做到这一点，但有一个函数可以用来获得所需的结果：CGImageCreateWithImageInRect(CGImageRef, CGRect)将帮助你。
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情况下裁剪视网膜图像，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;
}
您可以创建一个 UIImage 类别并在任何需要的地方使用它。基于 HitScans 的响应和下面的评论。
@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
你可以这样使用它：
UIImage *imageToCrop = <yourImageToCrop>;
CGRect cropRect = <areaYouWantToCrop>;
//for example
//CGRectMake(0, 40, 320, 100);
UIImage *croppedImage = [imageToCrop crop:cropRect];
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
在此桥接功能的帮助下CGRectMake-> CGRect（此答案由 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;
}
注意：所有这些答案都假设一个CGImage支持的图像对象。
image.CGImageUIImage如果由 a 支持，则可以返回 nil，CIImage如果您使用 a 创建此图像就是这种情况CIFilter。
在这种情况下，您可能必须在新的上下文中绘制图像，并返回该图像（慢）。
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;
}
这里没有一个答案能 100% 正确处理所有的比例和旋转问题。这是到目前为止所说的所有内容的综合，截至 iOS7/8 的最新版本。它应该作为一种方法包含在 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);
我看到的大多数响应只处理 (x, y) 的 (0, 0) 位置。好的，这是一种情况，但我希望我的裁剪操作能够居中。我花了一段时间才弄清楚 WTF 评论后面的那一行。
让我们以纵向拍摄的图像为例：
希望这是有道理的！如果没有，请尝试不同的值，您会发现在为您的cropRect 选择正确的 x、y、宽度和高度时，逻辑是相反的。
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)
}
}
快速扩展
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
}
}
在Swift中裁剪 UIImage 的最佳解决方案，在精度、像素缩放方面......：
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
下面的代码片段可能会有所帮助。
import UIKit
extension UIImage {
func cropImage(toRect rect: CGRect) -> UIImage? {
if let imageRef = self.cgImage?.cropping(to: rect) {
return UIImage(cgImage: imageRef)
}
return nil
}
}
看起来有点奇怪，但效果很好，并且考虑了图像方向：
var image:UIImage = ...
let img = CIImage(image: image)!.imageByCroppingToRect(rect)
image = UIImage(CIImage: img, scale: 1, orientation: image.imageOrientation)
- (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;
}
Swift 2.0 更新（CIImage兼容性）
扩展Maxim 的答案，但如果您的图像是CIImage基于的，也可以使用。
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
}
}
关注@Arne 的回答。我只是固定到类别功能。把它放在 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;
}
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
}
}
这是基于Noodles答案的更新 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
}
在 iOS9.2SDK 上，我使用下面的方法将帧从 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;
}
我对其他解决方案不满意，因为它们要么绘制了几次（使用了不必要的功率），要么有方向问题。这是我从 UIImage * 图像中用于缩放正方形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 scale = self.sourceImage.size.width / self.scrollView.contentSize.width;
UIImage *finalImage = nil;
CGRect targetFrame = CGRectMake((self.scrollView.contentInset.left + self.scrollView.contentOffset.x) * 比例，
(self.scrollView.contentInset.top + self.scrollView.contentOffset.y) * 比例，
self.cropSize.width * 比例，
self.cropSize.height * 比例）；
CGImageRef contextImage = CGImageCreateWithImageInRect([[self imageWithRotation:self.sourceImage] CGImage], targetFrame);
如果（上下文图像！= NULL）{
finalImage = [UIImage imageWithCGImage:contextImage
规模：self.sourceImage.scale
方向：UIImageOrientationUp];
CGImageRelease(contextImage);
}
返回最终图像；
}
- (UIImage *)imageWithRotation:(UIImage *)image {
if (image.imageOrientation == UIImageOrientationUp) 返回图片；
CGAffineTransform 变换 = CGAffineTransformIdentity;
开关（image.imageOrientation）{
案例 UIImageOrientationDown：
案例 UIImageOrientationDownMirrored：
变换 = CGAffineTransformTranslate（变换，image.size.width，image.size.height）；
变换 = CGAffineTransformRotate（变换，M_PI）；
休息;
案例 UIImageOrientationLeft：
案例 UIImageOrientationLeftMirrored：
变换 = CGAffineTransformTranslate(变换, image.size.width, 0);
变换 = CGAffineTransformRotate（变换，M_PI_2）；
休息;
案例 UIImageOrientationRight：
案例 UIImageOrientationRightMirrored：
变换 = CGAffineTransformTranslate(变换, 0, image.size.height);
变换 = CGAffineTransformRotate（变换，-M_PI_2）；
休息;
案例 UIImageOrientationUp：
案例 UIImageOrientationUpMirrored：
休息;
}
开关（image.imageOrientation）{
案例 UIImageOrientationUpMirrored：
案例 UIImageOrientationDownMirrored：
变换 = CGAffineTransformTranslate(变换, image.size.width, 0);
变换 = CGAffineTransformScale(变换, -1, 1);
休息;
案例 UIImageOrientationLeftMirrored：
案例 UIImageOrientationRightMirrored：
变换 = CGAffineTransformTranslate(变换, image.size.height, 0);
变换 = CGAffineTransformScale(变换, -1, 1);
休息;
案例 UIImageOrientationUp：
案例 UIImageOrientationDown：
案例 UIImageOrientationLeft：
案例 UIImageOrientationRight：
休息;
}
// 现在我们将底层的 CGImage 绘制到一个新的上下文中，应用变换
// 上面计算。
CGContextRef ctx = CGBitmapContextCreate(NULL, image.size.width, image.size.height,
CGImageGetBitsPerComponent(image.CGImage), 0,
CGImageGetColorSpace(image.CGImage),
CGImageGetBitmapInfo(image.CGImage));
CGContextConcatCTM(ctx, 变换);
开关（image.imageOrientation）{
案例 UIImageOrientationLeft：
案例 UIImageOrientationLeftMirrored：
案例 UIImageOrientationRight：
案例 UIImageOrientationRightMirrored：
// 嘎嘎...
CGContextDrawImage(ctx, CGRectMake(0, 0, image.size.height, image.size.width), image.CGImage);
休息;
默认：
CGContextDrawImage(ctx, CGRectMake(0, 0, image.size.width, image.size.height), image.CGImage);
休息;
}
// 现在我们只是从绘图上下文中创建一个新的 UIImage
CGImageRef cgimg = CGBitmapContextCreateImage(ctx);
UIImage *img = [UIImage imageWithCGImage:cgimg];
CGContextRelease(ctx);
CGImageRelease(cgimg);
返回图片；
}
斯威夫特 5.0 更新
public extension UIImage {
func cropped(rect: CGRect) -> UIImage? {
if let image = self.cgImage!.cropping(to: rect) {
return UIImage(cgImage: image)
} else if let image = (self.ciImage)?.cropped(to: rect) {
return UIImage(ciImage: image)
}
return nil
}
}