I'm currently trying to use the "Move" button (76x76) to represent Left/Up/Right arrows. I took a screenshot from the previewer, opened PhotoShop, pasted the screenshot, rotated it, removed all the black with the Magic Wand Tool, saved and imported in my map.
Then, I set this new icon as the Hero Icon of a unit, launch a map-test, but see that what was transparent now became black.

How am I supposed to proceed?

EDIT: Extension used: .tga

.TGA supports transparency?

It does on World of Warcraft through alpha channels.

You need to make sure that your Photoshop is saving the .TGA with transparency, apparently it needs a plugin or something. I was trying to say that in less words.

Quote from poison_us

You need to make sure that your Photoshop is saving the .TGA with transparency, apparently it needs a plugin or something. I was trying to say that in less words.

No idea how to make sure about that.

@Devlin: so I am supposed to put a full background layer with an alpha of 0 instead of nothing?

No, you mess with the alpha channels. What you would need to do is select everything that you want to remain visible, go into the Channels tab, add a new channel (Alpha), and fill the selected area with white. If you can save the tga with transparency, all the black part of that Channel should become invisible. That's how it works when adding images to WoW, at least.

Why not use .dds?

Anyway, in GIMP you go to Colour->Colour to Alpha and it will convert the chosen colour to alpha. There should be something similar in photoshop. The colour you should use would be the black that you deleted.

I prefer dds, much easier to use by the sounds of it.

I can't use .dd: somehow, my PhotoShop doesn't allow me to Save As a DDS.

Quote from payne

I can't use .dd: somehow, my PhotoShop doesn't allow me to Save As a DDS.

Textures, Icons, and GUI Resources
Photoshop dds plugin broski

Quote from payne

Choose DXT5 for the top dropdown box, turn off mip maps until you save (when you save your file, you want mipmaps, when you load them you don't) and leave the 2D texture as 2D texture. Nothing else should need changing, just hit save after that.

Quote from Jack[RCDF

Quote from payne

Choose DXT5 for the top dropdown box, turn off mip maps until you save (when you save your file, you want mipmaps, when you load them you don't) and leave the 2D texture as 2D texture. Nothing else should need changing, just hit save after that.

1) How to tell him not to load with mipmaps? And seeing this window is for Saving, I just leave it as "Generate MIP maps" right?
2) So now I can remove the black background and leave the transparent region?

Quote from payne

Quote from Jack[RCDF

Quote from payne

Choose DXT5 for the top dropdown box, turn off mip maps until you save (when you save your file, you want mipmaps, when you load them you don't) and leave the 2D texture as 2D texture. Nothing else should need changing, just hit save after that.

1) How to tell him not to load with mipmaps? And seeing this window is for Saving, I just leave it as "Generate MIP maps" right?
2) So now I can remove the black background and leave the transparent region?

1) Hit the button for No MipMaps. And yep.
2) Should be able to, but if not there should be a way to turn a colour into an alpha map. Google it.

It worked.
Thank you.