Paint.NET forum user Tanel asked for a Gaussian Blur function where the user could specify a different amount of blur for each channel (Red, Green, Blur, and Alpha). Here is my take on the problem.
The Idea
My thought was to modify the Gaussian Blur code to blur only the selected channel. I started with the Code that Illnab1024 sent me and just started making changes. I used CodeLab so that I wouldn't have to worry too much about a UI. The rest came easy. I'm familiar enough with the Gaussian Blur code at this point that these changes only took me about 15 minutes.
Please note that this effect shows up under the Effects > Blurs sub menu.
The Effect DLL
You can download the precompiled effect DLL here: GaussianBlurPlus.dll
Just drop this file in your \program files\Paint.NET\effects directory and you should be all set.
If you need help installing effects, read this page: Installing Effects
Instructions for Use
To use this plugin, simply select the channel you want to blur, then the amount of blur:
Then, click OK to finalize your image.
Here are some examples:
Tanel was happy with the plugin. In fact, he's written at least one tutorial using it (along with my Transparency Adjustment plugin).
I hope you enjoy it too.