我有一些代码来调整图像的大小，这样我就可以得到图像中心的缩放块-我用这个来获取一个UIImage，并返回一个小的，正方形的图像表示，类似于在照片应用程序的相册视图中看到的。(我知道我可以使用UIImageView和调整裁剪模式来实现相同的结果，但这些图像有时显示在UIWebViews中)。
我已经开始注意到这段代码中的一些崩溃，我有点难住了。我有两种不同的理论，不知道哪一种是正确的。
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。因为我想要图像的中心部分，所以我将传递给drawwinrect的CGRect参数设置为比图像上下文的边界更大的值。我希望这是符合规定的，但我是不是在试图掩盖其他我不应该触及的记忆?
理论2)我在后台线程中做所有这些。我知道UIKit的某些部分被限制在主线程中。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，我真怀念NSImage的drawwinrect:fromRect:operation:fraction:方法。)
当前回答
- (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;
}
其他回答
wolf回答的快速版本，对我来说很管用:
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
}
}
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;
}
Swift 2.0更新(CIImage兼容)
扩展马克西姆的答案，但如果您的图像是基于CIImage的，也是有效的。
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
}
}
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;
}
swift3
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)
}
}
