简而言之，以下代码的目的是根据目标大小和乘数(1x、2x、3x)调整图像大小。这工作正常，除了出于某种原因我还没有确定一些图像正在旋转。

public void ResizeImage(TargetSize targetSize, ResizeMultiplier multiplier, Stream input, Stream output)
{
    using (var image = Image.FromStream(input))
    {
        // Calculate the resize factor
        var scaleFactor = targetSize.CalculateScaleFactor(image.Width, image.Height);
        scaleFactor /= (int)multiplier; // Enum is effectively named constant with a value of 1, 2, or 3

        var newWidth = (int)Math.Floor(image.Width / scaleFactor);
        var newHeight = (int)Math.Floor(image.Height / scaleFactor);
        using (var newBitmap = new Bitmap(newWidth, newHeight))
        {
            using (var imageScaler = Graphics.FromImage(newBitmap))
            {
                imageScaler.CompositingQuality = CompositingQuality.HighQuality;
                imageScaler.SmoothingMode = SmoothingMode.HighQuality;
                imageScaler.InterpolationMode = InterpolationMode.HighQualityBicubic;

                var imageRectangle = new Rectangle(0, 0, newWidth, newHeight);
                imageScaler.DrawImage(image, imageRectangle);

                newBitmap.Save(output, image.RawFormat);
            }
        }
    }
}

// Class definition for the class used in the method above
public class TargetSize
{
    /// <summary>
    /// The _width
    /// </summary>
    private readonly int _width;

    /// <summary>
    /// The _height
    /// </summary>
    private readonly int _height;

    /// <summary>
    /// Initializes a new instance of the <see cref="TargetSize"/> class.
    /// </summary>
    /// <param name="width">The width.</param>
    /// <param name="height">The height.</param>
    public TargetSize(int width, int height)
    {
        _height = height;
        _width = width;
    }

    /// <summary>
    /// Calculates the scale factor.
    /// </summary>
    /// <param name="width">The width.</param>
    /// <param name="height">The height.</param>
    /// <returns></returns>
    public decimal CalculateScaleFactor(int width, int height)
    {
        // Scale proportinately
        var heightScaleFactor = decimal.Divide(height, _height);
        var widthScaleFactor = decimal.Divide(width, _width);

        // Use the smaller of the two as the final scale factor so the image is never undersized.
        return widthScaleFactor > heightScaleFactor ? heightScaleFactor : widthScaleFactor;
    }
}

// NUnit integration test case I'm using to exercise the above code
[Test]
public void ResizeImage_Persistant_Single()
{
    // Read the image from disk
    using (var fileStream = File.OpenRead(@"TestData\dog.jpg"))
    {
        using (var outputStream = new MemoryStream())
        {
            // Call the resize image method detailed above. ResizeMultiplier.Medium casts to 2.
            _sut.ResizeImage(new TargetSize(200, 200), ResizeMultiplier.Medium, fileStream, outputStream);
            using (var newImage = Image.FromStream(outputStream))
            {
                // Save the resized image to disk
                newImage.Save(@"TestData\ImageResizerTests.ResizeImage_Persistant_Single.jpg");
            }
        }
    }
}

例如这张图片:

适当缩放但这张图片:

颠倒了。值得一提的是，图片在预览区上传到本站时，也出现了上下颠倒的现象。这个事实(我显然刚刚发现)强烈地让我觉得这张照片有些有趣。不管我的代码需要处理它。

Imgur“修复”了上面的文件(因为当我通过我的代码运行它时它现在不旋转)所以我将它上传到 Google Drive 。如果您右键单击图像(在 FireFox 中我没有测试过其他浏览器)并单击 Save Image As... 那么图像不会随着我上面的代码旋转。如果您单击标题中的下载按钮，那么图像会随着我的代码旋转……这里是 another copy用我的代码翻转 180 度的狗图像。这一切都非常奇怪，我不知道我做错了什么......

需要说明的是，我的目标是在不旋转图像的情况下调整图像大小。

最佳答案

感谢 Chris Farmer 的大力帮助¹ 和 Mark Ransom ² 我能够回答我自己的问题。

核心问题是某些图像上的 EXIF 数据改变了图像的方向。当我调整图像大小时，所有 EXIF 数据都被剥离了。由于 EXIF 数据被剥离，观看者不知道图像的方向应该不同。这使我认为调整大小的代码正在旋转一些图像。值得注意的是，当您在 Windows 资源管理器中右键单击图像时，此方向信息不会显示在详细信息 View 中。您需要在图像属性对象中搜索它或使用像 this one 这样的在线 View 。 .

使用 data from here ³ 我能够创建以下命名常量:

private const int OrientationKey = 0x0112;
private const int NotSpecified = 0;
private const int NormalOrientation = 1;
private const int MirrorHorizontal = 2;
private const int UpsideDown = 3;
private const int MirrorVertical = 4;
private const int MirrorHorizontalAndRotateRight = 5;
private const int RotateLeft = 6;
private const int MirorHorizontalAndRotateLeft = 7;
private const int RotateRight = 8;

使用这些命名常量，我扩展了我的 ResizeImage 方法来读取:

public void ResizeImage(TargetSize targetSize, ResizeMultiplier multiplier, Stream input, Stream output)
{
    using (var image = Image.FromStream(input))
    {
        // Calculate the resize factor
        var scaleFactor = targetSize.CalculateScaleFactor(image.Width, image.Height);
        scaleFactor /= (int)multiplier; 

        var newWidth = (int)Math.Floor(image.Width / scaleFactor);
        var newHeight = (int)Math.Floor(image.Height / scaleFactor);
        using (var newBitmap = new Bitmap(newWidth, newHeight))
        {
            using (var imageScaler = Graphics.FromImage(newBitmap))
            {
                imageScaler.CompositingQuality = CompositingQuality.HighQuality;
                imageScaler.SmoothingMode = SmoothingMode.HighQuality;
                imageScaler.InterpolationMode = InterpolationMode.HighQualityBicubic;

                var imageRectangle = new Rectangle(0, 0, newWidth, newHeight);
                imageScaler.DrawImage(image, imageRectangle);

                // Fix orientation if needed.
                if (image.PropertyIdList.Contains(OrientationKey))
                {
                    var orientation = (int)image.GetPropertyItem(OrientationKey).Value[0];
                    switch (orientation)
                    {
                        case NotSpecified: // Assume it is good.
                        case NormalOrientation:
                            // No rotation required.
                            break;
                        case MirrorHorizontal:
                            newBitmap.RotateFlip(RotateFlipType.RotateNoneFlipX);
                            break;
                        case UpsideDown:
                            newBitmap.RotateFlip(RotateFlipType.Rotate180FlipNone);
                            break;
                        case MirrorVertical:
                            newBitmap.RotateFlip(RotateFlipType.Rotate180FlipX);
                            break;
                        case MirrorHorizontalAndRotateRight:
                            newBitmap.RotateFlip(RotateFlipType.Rotate90FlipX);
                            break;
                        case RotateLeft:
                            newBitmap.RotateFlip(RotateFlipType.Rotate90FlipNone);
                            break;
                        case MirorHorizontalAndRotateLeft:
                            newBitmap.RotateFlip(RotateFlipType.Rotate270FlipX);
                            break;
                        case RotateRight:
                            newBitmap.RotateFlip(RotateFlipType.Rotate270FlipNone);
                            break;
                        default:
                            throw new NotImplementedException("An orientation of " + orientation + " isn't implemented.");
                    }
                }
                newBitmap.Save(output, image.RawFormat);
            }
        }
    }
}

细心的人会注意到大部分附加代码都被提取了 from this answer一个相关的问题。

¹:^{谁是对的，但我不明白他的目的。}

²:^{谁向我展示了 Chris Farmer 想说的话。}

³:^{Orientation 键值为 confirmed here .}

关于c# - 调整大小时，某些图像正在旋转，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/33310562/