Question

好像当我用相机以纵向模式拍照时，UIImage具有正确的尺寸/宽高比（1536x2048 / 3：4）和方向（右），导出到文件（使用UIImage.AsPNG().Save()）时，它总是以横向模式显示（2048x1536,4：3）。

这是真的吗，还是我做错了什么？是否有解决方法，例如与ALAssetsLibrary.WriteImageToSavedPhotosAlbum？

更新：最初我认为这也发生在UIImage.SaveToPhotosAlbum()，但仔细观察后我发现UIImage在这种情况下不是来自相机的原件，但是而是从之前AsPNG()个已保存的数据重新构建的。

再次更新：看起来这是iPhone相机的一般“功能”，修复它的唯一方法是手动旋转图像。我尝试将this code移植到MT，如下所示，但我似乎已经发明了一种创建正确大小和宽高比的空白图像的新方法。谁能发现这个bug？

public static class ImageUtils
{
    static float DefaultMaxSize = 960;

    public static UIImage ScaleAndRotateImage (UIImage image) {
        return ScaleAndRotateImage(image, DefaultMaxSize);
    }

    public static UIImage ScaleAndRotateImage (UIImage image, float maxSize)
    {
        CGImage imgRef = image.CGImage;

        float width = imgRef.Width;
        float height = imgRef.Height;

        CGAffineTransform transform = CGAffineTransform.MakeIdentity();

        RectangleF bounds = new RectangleF (0, 0, width, height);
        if (width > maxSize || height > maxSize) {
            float ratio = width / height;
            if (ratio > 1) {
                bounds.Width = maxSize;
                bounds.Height = bounds.Width / ratio;
            } else {
                bounds.Height = maxSize;
                bounds.Width = bounds.Height * ratio;
            }
        }

        float scaleRatio = bounds.Width / width;
        SizeF imageSize = new SizeF (imgRef.Width, imgRef.Height);
        float boundHeight;
        UIImageOrientation orient = image.Orientation;
        if (orient == UIImageOrientation.Up) {
            //EXIF = 1
            transform = CGAffineTransform.MakeIdentity();
        } else if (orient == UIImageOrientation.UpMirrored) {
            //EXIF = 2
            transform = CGAffineTransform.MakeTranslation (imageSize.Width, 0);
            transform.Scale (-1.0f, 1.0f);
        } else if (orient == UIImageOrientation.Down) {
            //EXIF = 3
            transform = CGAffineTransform.MakeTranslation (imageSize.Width, imageSize.Height);
            transform.Rotate ((float) Math.PI);
        } else if (orient == UIImageOrientation.DownMirrored) {
            //EXIF = 4
            transform = CGAffineTransform.MakeTranslation (0, imageSize.Height);
            transform.Scale (1.0f, -1.0f);
        } else if (orient == UIImageOrientation.LeftMirrored) {
            //EXIF = 5
            boundHeight = bounds.Height;
            bounds.Height = bounds.Width;
            bounds.Width = boundHeight;
            transform = CGAffineTransform.MakeTranslation (imageSize.Height, imageSize.Width);
            transform.Scale (-1.0f, 1.0f);
            transform.Rotate ((float)(3.0f * Math.PI / 2.0));
        } else if (orient == UIImageOrientation.Left) {
            //EXIF = 6
            boundHeight = bounds.Height;
            bounds.Height = bounds.Width;
            bounds.Width = boundHeight;
            transform = CGAffineTransform.MakeTranslation (0, imageSize.Width);
            transform.Rotate ((float)(3.0f * Math.PI / 2.0));
        } else if (orient == UIImageOrientation.RightMirrored) {
            //EXIF = 7
            boundHeight = bounds.Height;
            bounds.Height = bounds.Width;
            bounds.Width = boundHeight;
            transform = CGAffineTransform.MakeScale (-1.0f, 1.0f);
            transform.Rotate ((float)(Math.PI / 2.0));
        } else if (orient == UIImageOrientation.Right) {
            //EXIF = 8
            boundHeight = bounds.Height;
            bounds.Height = bounds.Width;
            bounds.Width = boundHeight;
            transform = CGAffineTransform.MakeTranslation (imageSize.Height, 0);
            transform.Rotate ((float)(Math.PI / 2.0));
        } else {
            throw new InvalidOperationException ("Invalid image orientation");
        }

        UIGraphics.BeginImageContext(bounds.Size);

        CGContext context = UIGraphics.GetCurrentContext ();

        if (orient == UIImageOrientation.Right || orient == UIImageOrientation.Left) {
            context.ScaleCTM (-scaleRatio, scaleRatio);
            context.TranslateCTM (-height, 0f);
        } else {
            context.ScaleCTM (scaleRatio, -scaleRatio);
            context.TranslateCTM (0f, -height);
        }

        context.ConcatCTM(transform);

        context.DrawImage (new RectangleF(0, 0, width, height), imgRef);
        UIImage imageCopy = UIGraphics.GetImageFromCurrentImageContext ();
        UIGraphics.EndImageContext ();

        return imageCopy;
    }
}

Answer 1

在此处找到答案：CGContextDrawImage draws image upside down when passed UIImage.CGImage：使用UIImage.Draw()而不是CGContext.DrawImage()。结果代码：

public static UIImage Rotate(UIImage orig) {
    float w0 = orig.Size.Width;
    float h0 = orig.Size.Height;

    UIGraphics.BeginImageContext(new SizeF(w0, h0));
    orig.Draw(new RectangleF(0, 0, w0, h0));
    UIImage imageCopy = UIGraphics.GetImageFromCurrentImageContext ();
    UIGraphics.EndImageContext ();

    return imageCopy;
}

这会生成正确大小，宽高比和方向的图像，但方向始终为“向上”。

Answer 2

我终于开始工作了。这是一个有代码的要点：

https://gist.github.com/890460

和我的博客文章：

http://www.fastchicken.co.nz/2011/03/28/scaling-and-rotating-an-image-in-monotouch/

Answer 3

尝试通过UIImageJPEGRepresentation将UIImage转换为NSData，因为PNG图像不会保存图像方向值。

UIImage数据始终处于横向模式

3 个答案: