UIImage 数据始终处于横向模式

Question

似乎当我在纵向模式下使用相机拍照时，UIImage 具有正确的尺寸/长宽比（1536x2048 / 3:4）和方向（右），导出到文件（使用 UIImage.AsPNG().Save())，它始终以横向模式显示（2048x1536，4:3）。

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

更新：最初我认为UIImage.SaveToPhotosAlbum()也发生了这种情况，但经过仔细检查，我意识到这种情况下的UIImage并不是来自相机的原始数据，而是根据早期 AsPNG() 保存的数据重建的数据。

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。我尝试将此代码移植到MT，如下所示，但是什么我似乎所做的是发明一种新方法来创建正确尺寸和纵横比的空白图像。有人能发现这个错误吗？

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

我终于让这个工作了。这是一个包含代码的要点：

https://gist.github.com/890460

和我的博客文章关于它：

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

Answer 2

在这里找到答案： CGContextDrawImage 颠倒绘制图像当传递 UIImage.CGImage 时：使用 UIImage.Draw() 而不是 CGContext.DrawImage()。生成的代码：

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;
}

这会生成尺寸、纵横比和方向正确的图像，但方向始终为“向上”。

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。