I wanted to have a go at creating a wall decal, and couldn’t find a tutorial (maybe it’s completely obvious to anybody familiar with Photoshop?), so I thought I’d write my own. Disclaimer: I’m not an expert with graphics packages, and there may well be better/ more efficient ways of doing this…but I haven’t found them, and this is what I came up with after some experimentation.
I’m using GIMP. If anybody knows of a similar tutorial in Photoshop (or want to write one), let me know, I’d be happy to link to it or publish it.
First, choose your picture, drawing, whatever…. In this tutorial, the starting point will be this photograph I took on a grey day. I like the silhouette of the tree, but the sky is a bit blah. It has some texture…but not enough to be really interesting.
So the first step is to get rid of the sky and keep the outline of the tree.
Open the original picture, and duplicate the original layer (I always like to keep copies of originals…). Rename the original layer “Original” and name the new layer “BW” (optional, but for the purpose of this tutorial, it makes it easier to refer to layers by a name).
Select the “BW” layer. Go to Colours –> Treshold
The “Apply Treshold” dialog box below will appear, and at the same time, the layer will turn into pure black and white.
The “Apply Treshold” dialog box is where you choose the cut off point, by sliding the little black triangle left…
Or you can let Gimp decide by clicking the “Auto” button.
When you’re happy with the cutoff point, click “OK”.
In this example, I have also scaled the image to a square format, because I found this more visually appealing, but that is purely optional.
Now we have a perfectly clear cut black tree on a pure white background. The tree part is the decal, the white part we want to get rid of and replace with transparency.
To add transparency information, right click on the layer and select “Add alpha channel”. The alpha channel contains transparency information for an image, from white (totally opaque) to black (totally transparent), and all shades of grey/transparency in between.
Nothing actually happens that you can see, but you can check the alpha channel on the “channels” dialogue (if it’s not in the floating window on the right, go to Windows –> Dockable Dialogues –> Channels)
Before applying the alpha channel:
After applying the alpha channel:
At this point, duplicate the “BW” layer. Select the new layer, name it “DecalBlack”, and choose the Colour Tool (from the toolbox, or SHIFT + O).
Then click anywhere in the white area. This will mark all white pixels in the image as selected and they will start to shimmer at the edges.
Click the “Delete” key on your keyboard (or go to Edit –> Clear)
Poof! No more white areas. The grey checkered background means it’s transparent, althought the image will need to be saved in a format that supports transparency information (not all image formats do).
Choose Select –> None (or CTRL + SHIFT + A) to unselect everything.
We’re left with a black silhouette on a transparent background.
That’s fine, and we could stop here, but let’s make the black bits a bit more textured, by recycling the sky in the original picture.
Go back to the “Original” picture layer, duplicate it, use the rectangular tool to select an area of the sky and crop to selection.
Scale the result to the same size as the tree silhouette. Name that layer “Sky”.
Select the “DecalBlack” layer and duplicate it. Name this layer “DecalBlackTextured” and add a layer mask by selecting the layer, right clicking and choosing “Add Layer Mask”.
In the “Add Layer Mask” dialog box, select “Layer’s alpha channel” and click OK.
The layer mask will appear next to the original layer. Click on it to select it (it’s selected when there’s a white border around it).
Select the “Sky” layer, select all and copy.
Select the “DecalBlackTextured” layer and paste.
Select the pasted layer and anchor it (right click –> Anchor layer). The tree image takes on a slightly more ..textured… appearance (this is more noticeable if you zoom in. You can check the effect by adding a white layer underneath.)
You can of course paste it any other texture. Here I’ve done 3 more versions, with two of my textures (this one and this one) and one from bcommeberenice on Flickr, but I can’t find the exact texture to link to, sorry (I had downloaded it a white ago).
I’ve also done a version in white, by duplicating the “DecalBlack” layer, renaming it to “DecalWhite”, selecting everything, going to Colours –> Invert, then following the same process as above.
We’re nearly done.
To save the decal, make all the layers invisible except the one you want to use for the decal.
On the layer that will be the decal, click the tree silhouette to select it and unselect the layer mask.
Save a copy of the file as a TGA (I have read that SL supports the PNG format, which is another format that supports transparency, but that didn’t work for me, I lost all the transparency information when I uploaded the file as a PNG, I have no idea why – but I’ll stick to what worked): File –> Save a copy, change tthe file extension to TarGA image, Save (Merge Visible layers –> Export; Save)
Do this for all the decals you want to upload.
Upload the files.
Apply the texture to a prim.
The pictures below show each of the decalc applied a prim, first on a grey background, then on a green background, then with an orange tint applied.
From l to r
Decal white: White Render; Sky; Navy Render; BCommeBerenice texture
Decal black: White Render; Sky; Navy Render; BCommeBerenice texture