There are a few tutorials online on how to create a Team Fortress 2 spray decal with transparency, but as far as I know they all have problems. Some of which may have worked (for example, [this one]), but they start it off by telling you to create the image in Photoshop CS3, and then use a free software called [VTFEdit] to make it a decal. Not every one can afford to buy Photoshop.
Another [tutorial] is supposed to show you how to create an animated decal, but the author seems to lack the fundamental knowledge regarding image formats, and tries to convince people that JPEG supports transparency. (Hard to believe this tutorial was endorsed by MaximumPC. Major doodoo on their part.) Besides that, the author uses Photoshop as well.
But, there is a totally FREE way of creating a spray decal with transparency. Forget about Photoshop, or even the freeware VTFEdit (well, unless you want to create animated decals, but this is not what my blog entry is about). All you need is a free graphics software called [Paint.net], and the key is to save your image as a 32-bit uncompressed TGA. Now if you know what I am talking about, you are free to go and create your own decals.
For the rest of you readers, I will be showing the steps in making such a decal.
STEP 1. Of course you need to download and install paint.net first.
STEP 2. Create a new image, with width and height both being multiples of 16. For example, 64×256, 128×80 etc. Make sure to disable the anti-aliasing so you can construct your design using scratch lines and remove them easily by recoloring in the end.
STEP 3. Add a new layer.
STEP 4. Delete the background layer, so that only the newly added transparent layer is present. (You may choose to delete the background at the very end, but I personally prefer getting rid of it up front)
STEP 5. Do your magic – be artistic and creative, and make your decal as wierd as possible. Here is what I created. Notice the gray-and-white checker patterns that indicate transparency.
STEP 6. Save your image as a 32-bit uncompressed TGA. Make sure to uncheck “Compress (RLE)” or TF2 won’t be able to recognize the file format. In reality, you may want to do this step as often as possible throughout your creative process (in other words, save you files often so you won’t cry for mommy later when a sudden power failure takes place).
STEP 7. Fire up TF2. Go to Options, under the tab Multiplayer, you will be able to import the decal.
STEP 8. Test it out in a TF2 map.