编辑：从那以后，我发现这些实现都不适用于服务器端场景：微软不支持它们。所以不要去使用它们！
所以我在下面提供了两个单独的实现。我想我已经完成了 Windows 映像组件 (WIC) 的实现。
一些评论：
- GDI 实现似乎比 WIC 更快 - WIC @ 0.26s/photo, GDI @ 0.14s/photo)
- WIC 实现在多线程时没有看到任何性能提升，GDI 下降到 ~0.10s/照片
- 服务器端处理只支持 WIC，但是如果它不是多线程的，那么它就不能很好地扩展
- 在 i7 上运行，有问题的照片是由奥林巴斯相机创建的典型 1.2MB 图像
- 我的灵感来自http://weblogs.asp.net/bleroy/archive/2009/12/10/resizing-images-from-the-server-using-wpf-wic-instead-of-gdi.aspx
任何人都可以看到任何明显的东西吗？
using System;
using System.Collections.Generic;
using System.Diagnostics.Contracts;
using System.IO;
using System.Windows;
using System.Windows.Media;
using System.Windows.Media.Imaging;
namespace Mrwa.Bms.Common.Imaging
{
/// <summary>
/// Generates JPEG image previews for any supplied .NET image supported files
/// </summary>
/// <remarks>
/// WIC = Windows Imaging Component
/// http://weblogs.asp.net/bleroy/archive/2009/12/10/resizing-images-from-the-server-using-wpf-wic-instead-of-gdi.aspx
/// </remarks>
public class WicImagePreviewGenerator : IImagePreviewGenerator
{
private const int ScreenDpi = 96;
private BitmapFrame _imageFrame;
public WicImagePreviewGenerator(Stream stream)
{
Contract.Requires(stream != null);
try
{
if (stream.CanSeek) stream.Seek(0, SeekOrigin.Begin);
var decoder = BitmapDecoder.Create(stream, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.Default);
_imageFrame = decoder.Frames[0];
}
catch (NotSupportedException ex)
{
throw new ArgumentException("The image is corrupt.", "stream", ex);
}
}
public ImagePreviewGeneratorDto Generate(
int pixelSize, int jpegQuality = 80, int dpi = 72,
ImagePreviewGeneratorResizeQualityEnum resizeQuality = ImagePreviewGeneratorResizeQualityEnum.HighQuality)
{
int previewWidth;
int previewHeight;
CalculateDimensions(pixelSize, out previewWidth, out previewHeight);
// create a new target drawing canvas
var width = (int) (previewWidth*(ScreenDpi/(decimal) dpi));
var height = (int) (previewHeight*(ScreenDpi/(decimal) dpi));
var drawing = new ImageDrawing(
_imageFrame,
new Rect(0, 0, width, height));
var group = new DrawingGroup();
RenderOptions.SetBitmapScalingMode(group, GetScalingMode(resizeQuality));
group.Children.Add(drawing);
// generate the preview image frame
BitmapFrame previewFrame;
var previewVisual = new DrawingVisual();
using (var previewContext = previewVisual.RenderOpen())
{
previewContext.DrawDrawing(group);
previewContext.Close();
var previewBitmap = new RenderTargetBitmap(
previewWidth, previewHeight,
dpi, dpi,
PixelFormats.Default);
previewBitmap.Render(previewVisual);
previewFrame = BitmapFrame.Create(previewBitmap);
}
// generate the result as a JPG
using (var content = new MemoryStream())
{
var previewEncoder = new JpegBitmapEncoder { QualityLevel = jpegQuality };
previewEncoder.Frames.Add(previewFrame);
previewEncoder.Save(content);
content.Flush();
return new ImagePreviewGeneratorDto
{
Preview = content.ToArray(),
Width = previewWidth,
Height = previewHeight
};
}
}
// not used - retained for reference only
public IEnumerable<byte> GenerateOptimised(int pixelSize, int jpegQuality = 80)
{
int previewWidth;
int previewHeight;
CalculateDimensions(pixelSize, out previewWidth, out previewHeight);
var transform = new TransformedBitmap(
_imageFrame, new ScaleTransform(previewWidth, previewHeight, 0, 0));
var previewFrame = BitmapFrame.Create(transform);
// generate the result as a JPG
using (var result = new MemoryStream())
{
var previewEncoder = new JpegBitmapEncoder { QualityLevel = jpegQuality };
previewEncoder.Frames.Add(previewFrame);
previewEncoder.Save(result);
return result.ToArray();
}
}
private static BitmapScalingMode GetScalingMode(ImagePreviewGeneratorResizeQualityEnum previewQuality)
{
switch (previewQuality)
{
case ImagePreviewGeneratorResizeQualityEnum.HighQuality:
return BitmapScalingMode.HighQuality;
case ImagePreviewGeneratorResizeQualityEnum.HighSpeed:
return BitmapScalingMode.LowQuality;
default:
throw new NotSupportedException("Invalid preview quality specified.");
}
}
private void CalculateDimensions(int pixelSize, out int width, out int height)
{
var originalWidth = _imageFrame.PixelWidth;
var originalHeight = _imageFrame.PixelHeight;
// scale: reduce the longest side down to 'X' pixels and maintain the aspect ratio
if (originalWidth <= pixelSize && originalHeight <= pixelSize)
{
width = originalWidth;
height = originalHeight;
}
else if (originalWidth >= originalHeight)
{
width = pixelSize;
height = (int)((pixelSize / (decimal)originalWidth) * originalHeight);
}
else
{
width = (int)((pixelSize / (decimal)originalHeight) * originalWidth);
height = pixelSize;
}
}
#region IDisposable
private bool _disposed;
~WicImagePreviewGenerator()
{
Dispose(false);
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (_disposed) return;
if (disposing)
{
// free managed resources
_imageFrame = null;
}
// free unmanaged resources
_disposed = true;
}
#endregion
}
}
using System;
using System.Diagnostics.Contracts;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.IO;
using System.Linq;
namespace Mrwa.Bms.Common.Imaging
{
/// <summary>
/// Generates JPEG image previews for any supplied .NET image supported files
/// </summary>
/// <remarks>
/// Feel free to use this Client side. Not officially supported for back-end scenarios.
/// </remarks>
public class GdiPlusImagePreviewGenerator : IImagePreviewGenerator
{
private Image _image;
public GdiPlusImagePreviewGenerator(Stream stream)
{
Contract.Requires(stream != null);
try
{
if (stream.CanSeek) stream.Seek(0, SeekOrigin.Begin);
_image = Image.FromStream(stream);
}
catch (ArgumentException ex)
{
throw new ArgumentException("The image is corrupt.", "stream", ex);
}
}
private void CalculateDimensions(int pixelSize, out int width, out int height)
{
var originalWidth = _image.Width;
var originalHeight = _image.Height;
// scale: reduce the longest side down to 'X' pixels and maintain the aspect ratio
if (originalWidth <= pixelSize && originalHeight <= pixelSize)
{
width = originalWidth;
height = originalHeight;
}
else if (originalWidth >= originalHeight)
{
width = pixelSize;
height = (int)((pixelSize / (decimal)originalWidth) * originalHeight);
}
else
{
width = (int)((pixelSize / (decimal)originalHeight) * originalWidth);
height = pixelSize;
}
}
/// <remarks>
/// Not changing the colour depth; apparently the conversion can be quite poor
/// Don't forget to dispose of the stream
/// </remarks>
public ImagePreviewGeneratorDto Generate(
int pixelSize, int jpegQuality = 80, int dpi = 72,
ImagePreviewGeneratorResizeQualityEnum resizeQuality = ImagePreviewGeneratorResizeQualityEnum.HighQuality)
{
int previewWidth;
int previewHeight;
CalculateDimensions(pixelSize, out previewWidth, out previewHeight);
// resize the image (in terms of pixels) and standardise the DPI
using (var previewImage = new Bitmap(previewWidth, previewHeight))
{
previewImage.SetResolution(dpi, dpi);
using (var graphics = Graphics.FromImage(previewImage))
{
switch (resizeQuality)
{
case ImagePreviewGeneratorResizeQualityEnum.HighQuality:
graphics.SmoothingMode = SmoothingMode.HighQuality;
graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;
break;
case ImagePreviewGeneratorResizeQualityEnum.HighSpeed:
graphics.SmoothingMode = SmoothingMode.HighSpeed;
graphics.InterpolationMode = InterpolationMode.Low;
graphics.PixelOffsetMode = PixelOffsetMode.HighSpeed;
break;
default:
throw new NotSupportedException("Invalid Preview Quality Enum supplied.");
}
graphics.DrawImage(_image, new Rectangle(0, 0, previewWidth, previewHeight));
}
// convert to a JPG and reduce the quality
using (var content = new MemoryStream())
{
var jpegEncoder = GetEncoder(ImageFormat.Jpeg);
previewImage.Save(content, jpegEncoder,
new EncoderParameters
{
Param = new[] { new EncoderParameter(Encoder.Quality, jpegQuality) },
});
content.Flush();
// return the stream
return new ImagePreviewGeneratorDto
{
Preview = content.ToArray(),
Width = previewWidth,
Height = previewHeight
};
}
}
}
private static ImageCodecInfo GetEncoder(ImageFormat format)
{
var codecs = ImageCodecInfo.GetImageDecoders();
return codecs.FirstOrDefault(codec => codec.FormatID == format.Guid);
}
#region IDisposable
private bool _disposed;
~GdiPlusImagePreviewGenerator()
{
Dispose(false);
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (_disposed) return;
if (disposing)
{
// free managed resources
if (_image != null)
{
_image.Dispose();
_image = null;
}
}
// free unmanaged resources
_disposed = true;
}
#endregion
}
}