.NET位图对象 [英] .NET Bitmap Object

问题描述

我已将图像存储为数据库中的BLOB（Varbinary（max））。我将图像编码为.NET Bitmap TIFF。在页面上显示图像时，我可以将内容类型设置为JPEG，GIF等，并且图像始终在网页上正确显示。如果我将内容类型设置为TIFF（因为它被编码为TIF），我希望图像只能正确显示。我正在使用Bitmap类。我错过了什么吗？

以下是一些代码：

  objCmd.CommandText =SELECT Img FROM dbImage，其中id = 1 
 dr = objCmd.ExecuteReader 
 dr.Read（）
 
 screenshot = CType（dr（screenshot），Byte（））
 Response.ContentType =image / tiff
 Response.BinaryWrite（screenshot）
 Response.Flush（）
 Response.End（）
  

BLOB图像被编码为TIFF。但是，当提取图像时，它将以JPG和GIF显示。例如，如果我更改了response.contenttype到image / jpg，然后它仍然显示。问题是：为什么它仍然显示？我没有很多图像处理经验。

解决方案

它仍然显示的原因是因为现代浏览器忽略图像的内容类型标题（基于观察和测试，而不是文档）。几乎所有图像的前几个字节都会告诉你它的格式是什么 - 我假设浏览器（以及它们使用的图形库）看起来像这些字节（就像.NET一样），而不是依赖于内容类型的标题。 / p>

网络服务器没有重新编码图像

I have stored an image as a BLOB (Varbinary(max)) in a database. I encoded the image as a .NET Bitmap TIFF. When displaying the image on the page, I am able to set the content type as JPEG, GIF etc and the image always appears correctly on the web page. I would expect the image only to appear correctly if I set the content type as TIFF (as it was encoded as TIF). I am using the Bitmap class. Am I missing something?

Here is some code:

objCmd.CommandText = "SELECT Img FROM dbImage where id = 1
                dr = objCmd.ExecuteReader
                dr.Read()

                screenshot = CType(dr("screenshot"), Byte())
                Response.ContentType = "image/tiff"
                Response.BinaryWrite(screenshot)
                Response.Flush()
                Response.End()

The BLOB image was encoded as a TIFF. However, when extracting the image it will display in JPG and GIF. For example, if I changed response.contenttype to "image/jpg", then it still displays. The question is: why does it still display? I don't have a lot of experience with image processing.

解决方案

The reason it still displays is because modern browsers ignore the content-type header for images (based on observation and testing, not on documentation). The first few bytes of nearly every image will tell you what format it is in - I assume browsers (and the graphics libraries they use) look to these bytes (just as .NET does) instead of relying on the content-type header.

The web server is NOT re-encoding the image

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