进行UIImage的方形裁剪导致图像拉伸

Question

尝试执行UIImage的中心裁剪时，我得到以下结果（左为640*1136的原始图像，右为拟合为320*320的方形UIImageView的裁剪图像）：

变成：

我对比率元素进行了很多修改，以便它可以正确检测要修剪的量：使用图像的较短边，基于short_side/width_of_desired_rect构造一个比率，但是在这种情况下它似乎不起作用。 帮助赞赏！

- (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);

    //for retina consideration
    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;
}

Answer 1

尝试这个：

- (UIImage *)squareImageFromImage:(UIImage *)image scaledToSize:(CGFloat)newSize {
    CGAffineTransform scaleTransform;
    CGPoint origin;

    if (image.size.width > image.size.height) {
        CGFloat scaleRatio = newSize / image.size.height;
        scaleTransform = CGAffineTransformMakeScale(scaleRatio, scaleRatio);

        origin = CGPointMake(-(image.size.width - image.size.height) / 2.0f, 0);
    } else {
        CGFloat scaleRatio = newSize / image.size.width;
        scaleTransform = CGAffineTransformMakeScale(scaleRatio, scaleRatio);

        origin = CGPointMake(0, -(image.size.height - image.size.width) / 2.0f);
    }

    CGSize size = CGSizeMake(newSize, newSize);
    if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)]) {
        UIGraphicsBeginImageContextWithOptions(size, YES, 0);
    } else {
        UIGraphicsBeginImageContext(size);
    }

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextConcatCTM(context, scaleTransform);

    [image drawAtPoint:origin];

    image = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return image;
}

Answer 2

Swift3版本的fumoboy007的代码。

     func squareImage(img: UIImage, scaledToSize newSize: CGFloat) -> UIImage {
    var scaleTransform: CGAffineTransform
    var origin: CGPoint
    var image = img
    if image.size.width > image.size.height {
        let scaleRatio: CGFloat = newSize / image.size.height
        scaleTransform = CGAffineTransform(scaleX: scaleRatio, y: scaleRatio)
        origin = CGPoint(x: -(image.size.width - image.size.height) / 2.0, y: 0)
    }
    else {
        let scaleRatio: CGFloat = newSize / image.size.width
        scaleTransform = CGAffineTransform(scaleX: scaleRatio, y: scaleRatio)
        origin = CGPoint(x: 0, y: -(image.size.height - image.size.width) / 2.0)
    }
    let size = CGSize(width: newSize, height: newSize)
    if image.size.width > image.size.height {
        UIGraphicsBeginImageContextWithOptions(size, true, 0)
    }
    else {
        UIGraphicsBeginImageContext(size)
    }

    let context: CGContext? = UIGraphicsGetCurrentContext()
    context?.concatenate(scaleTransform)
    image.draw(at: origin)
    image = UIGraphicsGetImageFromCurrentImageContext()!
    UIGraphicsEndImageContext()
    return image
}

Answer 3

使用此代码调整图像大小

// Returns image resized to the desired CGSize
- (UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize {
    UIGraphicsBeginImageContext(newSize);
    [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

编辑：您基本上也在这里重画。 如果您要一遍又一遍地重复使用同一张图片，则最好一次调用一次并将结果保存为文件。 在以后的调用中加载该文件，而不是原始文件。

编辑2：好的，所以您要做的是保持宽高比，同时将图像调整为正方形。 上面的代码通过调整大小基本上将图像调整为正方形，但它没有保持宽高比。 保持纵横比的一种方法是找到缩小图像两个维度中较大的一个，然后将另一个维度缩小相同的因子。 让我知道您是否遇到麻烦。