我有一些调整图像大小的代码,所以我可以获得图像中心的缩放块 - 我使用它来获取UIImage并返回图像的小方形表示,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a UIImageView并调整裁剪模式以获得相同的结果,但这些图像有时会显示在中UIWebViews).
我已经开始注意到这段代码中的一些崩溃,我有点难过.我有两种不同的理论,我想知道是否有基础.
理论1)我通过绘制到目标大小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,我设置CGRect传递给的参数drawInRect大于我的图像上下文边界的东西.我希望这是犹太洁食,但我是否试图汲取我不应该触及的其他记忆？
理论2)我在后台线程中做了所有这些.我知道UIKit的部分内容仅限于主线程.我假设/希望绘制到屏幕外的视图不是其中之一.我错了吗？
(哦,我多么想念NSImage's drawInRect:fromRect:operation:fraction:方法.)
更新2014-05-28:我写这篇文章的时候iOS 3左右是热门的新东西,我确信现在还有更好的方法可以做到这一点,可能是内置的.正如许多人所提到的,这种方法不考虑轮换; 阅读一些额外的答案,并传播一些upvote爱,以保持对这个问题的回答对每个人都有帮助.
原始回复:
我打算将我的回复复制/粘贴到其他地方的同一问题:
没有简单的类方法可以做到这一点,但有一个功能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;
}
您可以制作UIImage类别并在任何需要的地方使用它.根据HitScans的回应和评论吼叫它.
@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 =; CGRect cropRect = ; //for example //CGRectMake(0, 40, 320, 100); UIImage *croppedImage = [imageToCrop crop:cropRect];
这是我的UIImage裁剪实现,它遵循imageOrientation属性.所有方向都经过了彻底的测试.
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;
}
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
借助这个桥梁功能CGRectMake- > CGRect(对此答案的回答@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:
抬头:所有这些答案都假设一个CGImage背景图像对象.
image.CGImage如果UIImage由a支持,则返回nil,如果CIImage使用a创建此图像,则会返回nil CIFilter.
在这种情况下,您可能必须在新的上下文中绘制图像,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;
}
这里没有任何答案100%正确处理所有比例和旋转问题.这是迄今为止所有内容的综合,是iOS7/8的最新版本.它意味着作为UIImage类别中的方法包含在内.
- (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;
}
Swift版本awolf的答案,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);
我见过的大多数响应只处理(0,0)(x,y)的位置.好吧,这是一个案例,但我希望我的裁剪操作集中.我花了一段时间才弄明白的是WTF评论之后的界限.
让我们以纵向拍摄的图像为例:
原始图像高度高于其宽度(Woo,到目前为止并不令人惊讶!)
CGImageCreateWithImageInRect方法在其自己的世界中想象的图像不是真正的肖像,而是景观(这也是为什么如果你不在imageWithCGImage构造函数中使用orientation参数,它将显示为180旋转).
所以,你应该想象它是一个风景,(0,0)位置是图像的右上角.
希望它有意义!如果没有,请尝试使用不同的值,在选择cropRect的正确x,y,宽度和高度时,您会看到逻辑被反转.
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
}
}
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)
}
}
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