When resizing some images

Question

In a nutshell, the goal of the following code is to resize the image based on the size of the target and the multiplier (1x, 2x, 3x). This works great, except that I have not determined that some images rotate.

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");
            }
        }
    }
}

For example, this image:

scales accordingly, but this image:

turned upside down. It is worth noting that the image also turned upside down when it was in the preview area to upload it to this site. The fact (which I obviously just discovered) strongly makes me think that something is funny with the image. No matter what my code should handle it.

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, /, . , 180 . ( 90 270 ). , newWidth, newHeight, scaleFactor, targetSize (private variables) image.Height/image.Width , 180 .

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Answer 1

Chris Farmer ¹ Mark Ransom ² .

, EXIF ​​ . , EXIF ​​ . EXIF ​​ , , -. , resizer . , Windows. -, .

³ :

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;

, ResizeImage :

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);
            }
        }
    }
}

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¹: ^{, , .}

²: ^{, .}

³: ^{Orientation .}