问题
After several days of tracking down bizarre GDI+ errors, I\'ve stumbled across this little gem on MSDN:
Classes within the System.Drawing namespace are not supported for use within a Windows or ASP.NET service. Attempting to use these classes from within one of these application types may produce unexpected problems, such as diminished service performance and run-time exceptions.
I don\'t know whether \"ASP.NET service\" means \"web application\" in this context, but \"diminished service performance\" certainly seems to cover the random assortment of \"A generic error occurred in GDI+\" and \"Out of memory\" errors that my app is throwing - intermittent, non-reproducible errors reading and writing JPEG images that - in many cases - were actually created by System.Drawing.Imaging in the first place.
So - if GDI+ can\'t read and write JPEG files reliably in a Web app, what should I be using instead?
I want users to be able to upload images (JPEG required, other formats nice-to-have), resample them reliably, and display useful error messages if anything goes wrong. Any ideas? Are the System.Media namespaces from WPF worth considering?
EDIT: Yeah, I know GDI+ works \"most of the time\". That\'s not good enough, because when it fails, it does so in a way that\'s impossible to isolate or recover from gracefully. I am not interested in examples of GDI+ code that works for you: I am looking for alternative libraries to use for image processing.
回答1:
There is an excellent blog post including C# code about using the ImageMagick graphics library through Interop over at TopTen Software Blog. This post deals specifically with running ASP.net on linux under mono; however, the C# code should be perfectly copy-paste-able, the only thing you'll need to change is the Interop attributes if you are running under windows referencing a window binary (DLL).
ImageMagick® is a software suite to create, edit, compose, or convert bitmap images. It can read and write images in a variety of formats (over 100) including DPX, EXR, GIF, JPEG, JPEG-2000, PDF, PhotoCD, PNG, Postscript, SVG, and TIFF. Use ImageMagick to resize, flip, mirror, rotate, distort, shear and transform images, adjust image colors, apply various special effects, or draw text, lines, polygons, ellipses and Bézier curves.
There is also an ImageMagick .Net development project on codeplex that wraps up everything for you. But it doesn't show active development since 2009, so it may be lagging behind the current ImageMagick library version. For a small trivial resizing routine, I'd probably stick with the interop. You just need to watch your implementation carefully for your own memory leak or unreleased resources (the library itself is well tested and vetted by the community).
The library is free and open source. The Apache 2 license appears to be compatible with both personal and commercial purposes. See ImageMagick License Page.
The library is totally cross platform and implements many powerful image handling and transformation routines that are not found in GDI+ (or not implemented under mono) and has a good reputation as an alternative for ASP.net image processing.
Update: Looks like there is an updated version of a .NET wrapper here: http://magick.codeplex.com/
回答2:
Yes, use the WPF System.Windows.Media classes. Being fully managed they don't suffer the same problems as the GDI stuff.
Here's an excerpt from some MVC code I use to render gradients, to give you an idea how to get from a WPF Visual to a PNG:
using System;
using System.IO;
using System.Web.Mvc;
using System.Windows;
using System.Windows.Media;
using System.Windows.Media.Imaging;
namespace MyMvcWebApp.Controllers
{
public class ImageGenController : Controller
{
// GET: ~/ImageGen/Gradient?color1=red&color2=pink
[OutputCache(CacheProfile = "Image")]
public ActionResult Gradient(Color color1, Color color2, int width = 1, int height = 30, double angle = 90)
{
var visual = new DrawingVisual();
using (DrawingContext dc = visual.RenderOpen())
{
Brush brush = new LinearGradientBrush(color1, color2, angle);
dc.DrawRectangle(brush, null, new Rect(0, 0, width, height));
}
return new FileStreamResult(renderPng(visual, width, height), "image/png");
}
static Stream renderPng(Visual visual, int width, int height)
{
var rtb = new RenderTargetBitmap(width, height, 96, 96, PixelFormats.Default);
rtb.Render(visual);
var frame = BitmapFrame.Create(rtb);
var encoder = new PngBitmapEncoder();
encoder.Frames.Add(frame);
var stream = new MemoryStream();
encoder.Save(stream);
stream.Position = 0;
return stream;
}
}
}
回答3:
You can find a very good article from a Microsoft Employee here: Resizing images from the server using WPF/WIC instead of GDI+ that proposes to use WPF instead of GDI+. It's more about thumbnailing but it's overall the same issues.
Anyway, at the end it states this:
I contacted the WPF team to have the final word on whether this is supported. Unfortunately, it's not, and the documentation is being updated accordingly. I apologize about any confusion this may have caused. We're looking at ways to make that story more acceptable in the future.
So WPF is also unsupported in web apps and still is I believe :-S
回答4:
ImageSharp
ImageSharp is an open-source cross-platform 2D graphics library. It's written in C# on top of the new .NET Standard, with no dependency on any OS-specific API.
It's currently still in pre-release on MyGet (you'll have to add the package source in the VS options or a NuGet.config file), but we are already using it with some very positive results.
回答5:
Most of the issues I have read about pertain to resources not being disposed properly.
I have used variants of this code time and time again with no issues from web applications:
public void GenerateThumbNail(HttpPostedFile fil, string sPhysicalPath,
string sOrgFileName,string sThumbNailFileName,
System.Drawing.Imaging.ImageFormat oFormat, int rez)
{
try
{
System.Drawing.Image oImg = System.Drawing.Image.FromStream(fil.InputStream);
decimal pixtosubstract = 0;
decimal percentage;
//default
Size ThumbNailSizeToUse = new Size();
if (ThumbNailSize.Width < oImg.Size.Width || ThumbNailSize.Height < oImg.Size.Height)
{
if (oImg.Size.Width > oImg.Size.Height)
{
percentage = (((decimal)oImg.Size.Width - (decimal)ThumbNailSize.Width) / (decimal)oImg.Size.Width);
pixtosubstract = percentage * oImg.Size.Height;
ThumbNailSizeToUse.Width = ThumbNailSize.Width;
ThumbNailSizeToUse.Height = oImg.Size.Height - (int)pixtosubstract;
}
else
{
percentage = (((decimal)oImg.Size.Height - (decimal)ThumbNailSize.Height) / (decimal)oImg.Size.Height);
pixtosubstract = percentage * (decimal)oImg.Size.Width;
ThumbNailSizeToUse.Height = ThumbNailSize.Height;
ThumbNailSizeToUse.Width = oImg.Size.Width - (int)pixtosubstract;
}
}
else
{
ThumbNailSizeToUse.Width = oImg.Size.Width;
ThumbNailSizeToUse.Height = oImg.Size.Height;
}
Bitmap bmp = new Bitmap(ThumbNailSizeToUse.Width, ThumbNailSizeToUse.Height);
bmp.SetResolution(rez, rez);
System.Drawing.Image oThumbNail = bmp;
bmp = null;
Graphics oGraphic = Graphics.FromImage(oThumbNail);
oGraphic.CompositingQuality = CompositingQuality.HighQuality;
oGraphic.SmoothingMode = SmoothingMode.HighQuality;
oGraphic.InterpolationMode = InterpolationMode.HighQualityBicubic;
Rectangle oRectangle = new Rectangle(0, 0, ThumbNailSizeToUse.Width, ThumbNailSizeToUse.Height);
oGraphic.DrawImage(oImg, oRectangle);
oThumbNail.Save(sPhysicalPath + sThumbNailFileName, oFormat);
oImg.Dispose();
}
catch (Exception ex)
{
Response.Write(ex.Message);
}
}
回答6:
You may have a look at http://gd-sharp.sourceforge.net/ which is a wrapper for the GD library. I haven't tested it but it seems promising.
回答7:
I've had good behavior from the Cairo library (http://www.cairographics.org) in an ASP.Net webserver environment. I actually moved to cairo from WPF due to WPF's poor memory usage model for web-based stuff.
WPF actually tends to run your worker process out of memory. None of the WPF objects implement IDisposable, and many of them reference unmanaged memory that's only freed via a finalizer. Heavy use of WPF (especially if your server is significantly CPU-taxed) will eventually run you out of memory because your finalizer queue gets saturated. When I was profiling my app, for instance, the finalization queue had upwards of 50,000 objects on it, many of them holding references to unmanaged memory. Cairo has behaved much better for me, and its memory usage pattern has been much more predictable than WPF's.
If you're interested in using cairo, grab the libs from GTK+'s website. They have an x86 as well as an x64 set of binaries.
The only downside is that cairo can't read/write JPG natively; however, you could easily adapt WPF's stuff for reading/writing JPG and do the resampling/scaling/drawing/whatever else using Cairo.
来源：https://stackoverflow.com/questions/1528525/alternatives-to-system-drawing-for-use-with-asp-net