C# - Outputting image to response output stream giving GDI+ error

Question

When outputting an image to the output stream, does it require temporary storage? I get the "generic GDI+" error that is usually associated with folder permission error when saving an image to file.

The only thing I'm doing to the image is adding some text. I still get the error even when I output the image straight without modifications. For example, doing this will give me the error:

using (Bitmap image = new Bitmap(context.Server.MapPath("images/stars_5.png"))) {     image.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Png); } 

Everything works fine on my local machine running Windows 7 with IIS 7.5 and ASP.NET 2.0. The problem is occurring on the QA server which is running Windows Server 2003 with IIS 6 and ASP.NET 2.0.

The line that's giving the error is:

image.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Png); 

Here's the stack trace:

[ExternalException (0x80004005): A generic error occurred in GDI+.]    System.Drawing.Image.Save(Stream stream, ImageCodecInfo encoder, EncoderParameters encoderParams) +378002    System.Drawing.Image.Save(Stream stream, ImageFormat format) +36    GetRating.ProcessRequest(HttpContext context) in d:\inetpub\wwwroot\SymInfoQA\Apps\tools\Rating\GetRating.ashx:54    System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +181    System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +75 

Answer 1

PNGs (and other formats) need to be saved to a seekable stream. Using an intermediate MemoryStream will do the trick:

using (Bitmap image = new Bitmap(context.Server.MapPath("images/stars_5.png"))) {    using(MemoryStream ms = new MemoryStream())    {       image.Save(ms, System.Drawing.Imaging.ImageFormat.Png);       ms.WriteTo(context.Response.OutputStream);    } } 

Answer 2

I just would add:

Response.ContentType = "image/png"; 

So it can be viewed directly in the browser when it isn't within an img tag.