UIScrollView 中图像上的cropImage 方法的问题会产生错误的图像

Question

我正在使用以下裁剪方法来裁剪位于 UIImageView 中的 uiimage，然后该 UIImageView 位于 UIScrollView 中。

-(UIImage *)cropImage:(UIImage *)image
{
    float scale = 1.0f/_scrollView.zoomScale;

    NSLog(@"Oh and heres that zoomScale: %f", _scrollView.zoomScale);

    CGRect visibleRect;
    visibleRect.origin.x = _scrollView.contentOffset.x * scale;
    visibleRect.origin.y = _scrollView.contentOffset.y * scale;
    visibleRect.size.width = _scrollView.bounds.size.width * scale;
    visibleRect.size.height = _scrollView.bounds.size.height * scale;

    NSLog(@"Oh and here's that CGRect: %f", visibleRect.origin.x);
    NSLog(@"Oh and here's that CGRect: %f", visibleRect.origin.y);
    NSLog(@"Oh and here's that CGRect: %f", visibleRect.size.width);
    NSLog(@"Oh and here's that CGRect: %f", visibleRect.size.height);

    CGImageRef imageRef = CGImageCreateWithImageInRect([image CGImage], visibleRect);
    UIImage *croppedImage = [[UIImage alloc] initWithCGImage:imageRef];
    CGImageRelease(imageRef);

    return croppedImage;
}

我需要将图像裁剪为 (321,115) 的 CGSize。在裁剪图像并查看打印结果后，我可以看到 visibleRect 是 (0,0,321,115) - 它应该是什么，croppedImage UIImage 然后具有宽度：321 和高度：115。但是由于某种原因，图像似乎完全放大得太远了（该方法将原始图像的一小部分裁剪为 321x115 的大小）。

为什么这种方法不能正确裁剪我的图像？

-附带说明：当我调用此方法时，我会像这样调用_croppedImage = [self cropImage:_imageView.image];，它将自定义 UIView 类的 UIImage 属性设置为裁剪后的图像。

Answer 1

请试试这个功能。它可能会帮助你。

参数：

1. UIImage
2. CGSize (321,115) 或任何大小

// 裁剪图像 - 图像将从完整图像中裁剪

- (UIImage *)cropImageWithImage:(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;
}

仅裁剪图像的选定部分

请查看this link