How to use transparent image as background on transparent winform? [duplicate]

This question already has answers here: Transparent images with C# WinForms 开发者_如何学编程 (6 answers) Closed 9 years ago.

I have a WinForm in C#, I have both BackCOlor and TransparencyKey set to color "Lime". If I compile at this point the form is transparent. Then I added an BackgroundImage with a Lime background (#00ff00), but the Lime on the image is not transparent.

How can I get the background image to have a transparent background too?

The image I used is a .bmp

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I'm pretty sure the Lime color in the picture is not identical to Lime you set as TransparencyKey.

Use ColorPicker: http://www.iconico.com/download.aspx?app=ColorPic&type=free

over your picture to see what color code the lime in the picture has: e.g. #XXXXXX. Then put that number in TransparencyKey, don't just use "Lime".

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Use an image format that supports transparency such as PNG.

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It works for me. Are you sure that the BMP has exactly the same background color as your form, and that it has not been altered some way, perhaps by a reduction in the number of colors or something similar?