您要的内容称为Alpha通道.不幸的是，GIF不支持它.摘自本文:

What you are asking for is called alpha channel. Unfortunately, it is not supported for GIFs. From this article:

TIFF，TGA，PNG，PSD和GIF均支持alpha，但实际上仅支持PNG和 GIF用于应用程序和Web.但是，Gif使用 特殊类型的Alpha.代替GIF图像中的Alpha通道 包含透明度，它仅具有打开/关闭透明度. 这意味着 GIF图像中的像素可以完全不透明 或完全透明.两者之间没有.

TIFF, TGA, PNG, PSD and GIF all support alpha but really only PNG and GIF are used for applications, and the web. Gif, however, uses a special type of alpha. Instead of the alpha channel in a GIF image containing degrees of transparency it only has an on/off transparency. This means that pixels within a GIF image can either be fully opaque or fully transparent. There is no in between.

可以通过程序以自定义不透明度绘制图像.看到这些:

It is possible to paint an image with custom opacity programmatically. See these:

• 使用Graphics.DrawImage()绘制图像透明/Alpha通道
• .DrawImage具有不透明度?
• 如何实施Alpha混合
• 使用GDI +进行Alpha混合

• Using Graphics.DrawImage() to Draw Image with Transparency/Alpha Channel
• .DrawImage with opacity?
• How to implement Alpha blending
• Alpha Blending using GDI+