transparent tilesets

I've been given a tileset with transparency to remix.

I've downloaded Paint.net to change it however whenever I do it and save the .png file the background becomes black on the Level Editor.

How can I keep the background transparent and still change the tileset?

When you're saving the new image, make sure the PNG format is set to 32 bit, as apparently Auto Detect might not work at all times. If this doesn't work, try using the GIMP.

That worked nicely thanks.

By the way, meanwhile I was trying other stuff and painting the background as that bright pink works as well.

If the tileset is properly transparent in the first place, GIMP won't mess it up; the same cannot be said for Paint.NET.

The Color to Alpha option is not intended to be used in that way.

The simplest way to ensure an image is transparent in GIMP is to simply give all the layers a fill color of "transparency."

Dib, I've never used that, but I understand it applies to entire layers, so I guess it's normal that all objects are affected, unless you use a different layer.

There are many ways to work with transparency in GIMP; for instance, if you need to make some tiles transparent, you could cut and paste them as a new layer at the same spot, while changing the layer's opacity.

Easier to use eraser with partial opacity, or paintbrush/pencil tool to draw at partial opacity first.

in GIMP, the best way (imo) to make transparency is to select what you want transparent on a layer, right-click on layer and click 'add layer mask'. then, pick 'black (full transparency)' and fill white into the selection. then, right-click layer and click 'apply layer mask' and voila!

In my opinion, the simplest way to do transparency in GIMP is to go to Layer>Transparency>Add Alpha Channel. This makes it so that erasing or deleting an area will make it transparent, instead of changing it to the background color.