Это код, который я использую. Он поддерживает вращение, а также устанавливает разрешение изображения в соответствии со стандартами JPEG 72dpi @ 24-bit color (по умолчанию GDI + сохраняет изображения с 96dpi @ 32-bit color). Это также устраняет проблему черной / серой границы, с которой некоторые люди сталкиваются при изменении размера изображений.
/// <summary>
/// Resizes and rotates an image, keeping the original aspect ratio. Does not dispose the original
/// Image instance.
/// </summary>
/// <param name="image">Image instance</param>
/// <param name="width">desired width</param>
/// <param name="height">desired height</param>
/// <param name="rotateFlipType">desired RotateFlipType</param>
/// <returns>new resized/rotated Image instance</returns>
public static Image Resize(Image image, int width, int height, RotateFlipType rotateFlipType)
{
// clone the Image instance, since we don't want to resize the original Image instance
var rotatedImage = image.Clone() as Image;
rotatedImage.RotateFlip(rotateFlipType);
var newSize = CalculateResizedDimensions(rotatedImage, width, height);
var resizedImage = new Bitmap(newSize.Width, newSize.Height, PixelFormat.Format32bppArgb);
resizedImage.SetResolution(72, 72);
using (var graphics = Graphics.FromImage(resizedImage))
{
// set parameters to create a high-quality thumbnail
graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
graphics.SmoothingMode = SmoothingMode.AntiAlias;
graphics.CompositingQuality = CompositingQuality.HighQuality;
graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;
// use an image attribute in order to remove the black/gray border around image after resize
// (most obvious on white images), see this post for more information:
// http://www.codeproject.com/KB/GDI-plus/imgresizoutperfgdiplus.aspx
using (var attribute = new ImageAttributes())
{
attribute.SetWrapMode(WrapMode.TileFlipXY);
// draws the resized image to the bitmap
graphics.DrawImage(rotatedImage, new Rectangle(new Point(0, 0), newSize), 0, 0, rotatedImage.Width, rotatedImage.Height, GraphicsUnit.Pixel, attribute);
}
}
return resizedImage;
}
/// <summary>
/// Calculates resized dimensions for an image, preserving the aspect ratio.
/// </summary>
/// <param name="image">Image instance</param>
/// <param name="desiredWidth">desired width</param>
/// <param name="desiredHeight">desired height</param>
/// <returns>Size instance with the resized dimensions</returns>
private static Size CalculateResizedDimensions(Image image, int desiredWidth, int desiredHeight)
{
var widthScale = (double)desiredWidth / image.Width;
var heightScale = (double)desiredHeight / image.Height;
// scale to whichever ratio is smaller, this works for both scaling up and scaling down
var scale = widthScale < heightScale ? widthScale : heightScale;
return new Size
{
Width = (int) (scale * image.Width),
Height = (int) (scale * image.Height)
};
}