I've taken a couple of photos of my school, for my school map.
Let's see how to convert this photo:
Into a Half-Life texture:
Alright, for this tutorial, I'll be using GIMP, because it's a free alternative to Abobe Photoshop. And, if you get used to the controls, it's going to be a good alternative >:D
If you follow the tutorial, you might even learn some useful GIMP shortcuts (and that's what tutorials are focused on: learning how to do stuff).
Open your raw photo:
Zoom in: (Hold Ctrl and use the mouse wheel)
You can click and hold the mouse wheel to move around, too :)
Now, select an area to crop: (Press R)
And when you select your area, press Enter to confirm the selection.
Now go to the tab
Image -> Crop to selection...
Image -> Scale image
Set it to 256x256. If the aspect ratio is locked, press the chain icon to the right.
You could use: 64x64, 128x128, 256x256 and 512x512. Sizes like 192, 240, 320 and 480 are OK, but usually not recommended, nor used :P
It's mostly your design choice. As for me, sometimes I use "modular" textures. Basically, they're like mipmaps, where 1 texture is more low-res than the original, and so on...
Then press Scale.
OK, we're not over yet. We need to make it seamless, because, well, it's seamed.
Press Ctrl+Shift+O (Hold Ctrl and Shift, then press O)
Now press Offset by x/2 y/2 (or Alt+2)
And press Offset. Now it will be split into 4 quadrants:
EWW, just LOOK AT THAT PIECE OF UGLINESS! AAARGH!
Let's correct this before I start vomiting, shall we?
Select this tool. And go to a certain area of your choice:
Hold Ctrl and click on that point. That is your reference point now.
Now paint it a bit, and play with the tool, you will then experience how it "behaves" :)
AHH, MUCH BETTER. :D
Also, don't forget to brush off some details there and there.
Let's press Ctrl+Shift+O again, and revert the quadrants:
Now, for the sake of stuff, we could apply a sharpening filter, or maybe add some contrast, but for now, we'll just make it as it is.
There, see? It's now ready to be used. Not yet, mister!
We need to make it compatible with Wally.
Image -> Mode -> Indexed
IMPORTANT: Don't set the colour number to 255. Set it to 256.
Thank you, Alberto309, for the hint :D
Use those settings, and then convert it to Indexed :)
Now, export your texture. Press Ctrl+Shift+E.
Name it with something that ends with *.bmp
The next step is crucial:
Use this configuration. GIMP must not write colour space info, otherwise the colours will get messed up in Wally.
Now, let's import this wall into Wally.
Open Wally, and then create/open a WAD file.
File -> New
And select "WAD" as a file type.
Basically, just drag'n'drop it into the WAD window:
And then save the WAD somewhere.
If I missed out a part, let me know, I'll correct it ASAP :)