调整大小后裁剪 UIImage 的底部

Question

我有这张图片（原始尺寸）

我想将图像的大小调整为 600 x 600 的纵横比。之后，我想只裁剪底部到此帧：{0, 400, 600, 200} 以获得图像的底部。

在保留纵横比的情况下调整大小效果很好，但我无法裁剪图像的底部。我正在使用此代码调整纵横比：

CGFloat horizontalRatio = bounds.width / self.size.width;
CGFloat verticalRatio = bounds.height / self.size.height;
CGFloat ratio;

switch (contentMode) {
    case UIViewContentModeScaleAspectFill:
        ratio = MAX(horizontalRatio, verticalRatio);
        break;

    case UIViewContentModeScaleAspectFit:
        ratio = MIN(horizontalRatio, verticalRatio);
        break;

    default:
        [NSException raise:NSInvalidArgumentException format:@"Unsupported content mode: %d", contentMode];
}

CGSize newSize = CGSizeMake(self.size.width * ratio, self.size.height * ratio);
UIImage *resizedImg = [self resizedImage:newSize interpolationQuality:quality];
if (UIViewContentModeScaleAspectFill == contentMode && (newSize.height > bounds.height || newSize.width > bounds.width)) {
    CGRect newRect = CGRectMake((newSize.width - bounds.width) / 2, (newSize.height - bounds.height) / 2, bounds.width, bounds.height);
    CGImageRef imageRef = CGImageCreateWithImageInRect([self CGImage], bounds);
    UIImage *croppedImage = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    return croppedImage;
}
return resizedImg;

这段代码用于裁剪底部

CGRect rect = CGRectMake(0, 400, 600, 200);
CGImageRef imageRef = CGImageCreateWithImageInRect([newImage CGImage], rect);
UIImage *cropped = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);

这就是我得到的结果（我应该得到相同的图像，我想让该裁剪模糊底部裁剪区域以显示一些文本）：

Answer 1

This 帮我解决了这个问题。我用错误的值初始化图像的框架。

Answer 2

很简单

- (UIImage *)cropImage:(UIImage *)oldImage {

CGSize imageSize = oldImage.size;

UIGraphicsBeginImageContextWithOptions( CGSizeMake( imageSize.width,
                                                    imageSize.height - 200),
                                        NO,
                                        0.);
[oldImage drawAtPoint:CGPointMake( 0, -100)
            blendMode:kCGBlendModeCopy
                alpha:1.];

UIImage *croppedImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

return croppedImage;
}

Answer 3

https://developer.apple.com/documentation/coregraphics/cgimage/1454683-cropping

这就是我的救命之恩！！

func cropImage(_ inputImage: UIImage, toRect cropRect: CGRect, viewWidth: CGFloat, viewHeight: CGFloat) -> UIImage? 
{    
let imageViewScale = max(inputImage.size.width / viewWidth,
                         inputImage.size.height / viewHeight)

// Scale cropRect to handle images larger than shown-on-screen size
let cropZone = CGRect(x:cropRect.origin.x * imageViewScale,
                      y:cropRect.origin.y * imageViewScale,
                      width:cropRect.size.width * imageViewScale,
                      height:cropRect.size.height * imageViewScale)

// Perform cropping in Core Graphics
guard let cutImageRef: CGImage = inputImage.cgImage?.cropping(to:cropZone)
else {
    return nil
}

// Return image to UIImage
let croppedImage: UIImage = UIImage(cgImage: cutImageRef)
return croppedImage
}