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

这是我的UIImage作物实现,它遵从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;
}

其他回答

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)
    }
}

我不满意的其他解决方案,因为他们要么画了几次(使用更多的权力比必要的)或有问题的方向。下面是我从UIImage *图像中使用的缩放正方形croppedImage。

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();

你可以创建一个UIImage类别,并在任何你需要的地方使用它。基于HitScans的响应和咆哮的评论。

@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

你可以这样用:

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

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

UIImage *croppedImage = [imageToCrop crop:cropRect];

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
    }
}
 (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;
}