I guess I can do a simple filtering tutorial on Paint.NET (ver 3.10). I used PS in the past, but it was in school so I didn't have it for personal use, and didn't know about GIMP until recently. I like Paint.NET because it's also free and fairly easy to use.
1. Warm Effect- With Paint.NET you don't really get the same result using the gaussian blur layer overlay as in PS, let me show you what you can do though.
So here is the original in-game pic I took with print screen key.
Not a bad pic quality, but in the original pic size the image is a bit blurry, and colors look faded. Let's fix that shall we?
Step 1. Go up to the menu bar and click on Effects, and you'll see a list of choices on a drop-down menu, choose Sharpen, a small window will pop up where you can adjust sharpness, for this tutorial I used x2, I don't really like to sharpen it too much, but up to x6 is a pretty good range.
Step 2. Let's see how it looks if I try the gaussian blur layer overlay, so duplicate the original layer, go to Effects and choose gaussian blur in the sub-menu, set it on 5 when a window pops-up. Then go to layer properties, and change the blending mode from normal to overlay. You'll end up with something like this.
The colors look more vibrant, but it doesn't really have the glowy effect that PS has. But hey, there's a glow effect so let's use that. For this example I used default setting for radius (6) and contrast (10), but set brightness to -20 since the glow effect really brightens the imgage on default setting. And tada, the final result looks like this.
Now it does have the glowy warm effect, you can adjust sharpeness again to your preference, I ended up using x6 sharpeness because I didn't want to lose the detail on the model's facial features.
2. Soften Portrait- So you have to go an extra step in Paint.NET to achieve warm effect, not bad, but for 3.10 version which just released, there's a new effect called "soften portrait", hey that sounds a lot like warm effect, let's see what this thing does.... start out with the same original pic, click on Effects and choose soften portrait, the pop-up window has 3 adjustments, for this example I used default settings for softness and warmth, but set lighting a bit higher at 10. And tada, cool looking image in just one step, no need to duplicate layer nor use glow effect. The colors are not as vibrant, but it's a different look. Adjusting the warmth will make the colors less brownish. But don't forget to sharpen it a little, I used x2.
You can also use the gaussian blur layer overlay for the first step, then instead of using glow, try soften portrait, and you get this.
You can definitely see the glowy effect now, and the image is quite dramatic.
That's the end of tutorial, hope it helps.