Advanced photoshop techniques
It's been a while since I wrote my last tutorial here and for the last couple of months I said to myself: you REALLY have to write some more tutorials but I never found time. Yesterday I received a really nice thank-you-message from one of the developers who appreciated the tutorial on how-to-build-a-instrument-background-from-scratch. Reason enough to recap a couple of new techniques which I developed over the last years and share the thoughts with you.
In this tutorial I try to explain a couple of steps that hopefully will enhance the overall look of all your textures. The methods described can be used for basically every part of your model. I am using an old photoshop version for my project, but most of the steps can be done in almost any other image processing tool.
I chose an 1930th headset of my Electra as an example. It's not a model that is particularly well done, but it's a good example for what I want to show you because it consists of many different materials and yet is a small and simple part. I won't go into the details of modelling here as the focus is on the work in photoshop.
Step 1 - gettin' started
What you always should start with is a blank texture, and for this part I am using a 512x512 pixel image. You will need a 'mesh' layer - by that I mean a representation of the UV mapping. If you are using Gmax, you can follow Bill L. advice and create this layer using lilithunwrap, I still do this manually by taking screenshots of the uv unwrap window in gmax and paste, mask and rescale it in photoshop. To make the layer more visible I usually add a background layer with some color, that also shows you empty sections of your texture for later. To help you identify the different parts I imposed a description layer to the screenshot.
Step 2 - the base
Let's give the parts some color! Select one area at the time and fill it with an appropriate color. At this stage it's not important to exactly match what you intend to do, it's more like a rough sketch. It can be beneficial to have ONE layer for each part you are working on, but that's up to you.
Note that I also added two dark lines and a dotted white line at the place of the leather headband. That'll be the stitching later on. I always like to apply a slight noise filter on these layers. It'll give you some basic structure.
Step 3 - the first magic trick
A really, really, REALLY nice trick is to add white lines along the hard contours of your 3d part. This will improve all your textures 10 fold! There are a couple of ways to do this. For instance you can paint some highlights manually - but it's very likely that you can't paint a straight line by hand (coffee and or beer consumption I suppose), therefore I recommend you use paths. If you haven't used paths before STOP RIGHT HERE! Paths are such a great tool in photoshop and you need to get your head around it! It'll help you draw these freakin' panel lines and rivets, differently colored sections on the fuselage, scratches aaaaaaaand these beautiful white lines we are making now.
Therefore: if you have no idea how paths are being used, read some tutorials on this topic before you continue with this tutorial .
What we want to achieve in step 4 are these highlighted edges for all sharp objects. That is one of the reasons why we need a very precise "mesh layer" - you need to know were these edges are in order to draw the lines. Lets get started and draw some paths along the edged of the mesh.
Remember that you want to have a path around every visible edge. The Ctrl-, Shift- and space keys are your friend, use them constantly, it'll save you a looooot of time! Once you finished that it'll look like this:
One of the good things about paths is of course that you can always come back and modify your lines if you're missing some edges or if you had drawn a line were there shouldn't be one. But for now it's OK and the obvious step is to get the highlights drawn. So create a new layer, deselect the last path you were working on (otherwise only this path gets stroked), Select a 1 px brush, white as foreground-brush-color and click on the little "stroke path".
You can hide the path afterwards by pressing Ctrl+Shift+h. In the following picture I also hid the mesh layer to show the result.
Here comes the next secret: make good use of the layer-blending-modes!
Blending modes are brilliant for merging two or more different graphics into one while reserving all details you want. If you have no idea what the different blending modes are for, take some time of NOW and read this tutorial . We'll need this knowledge later on as well. 
Let's apply this new knowledge to our edges. Select the white-edge-layer and set the blending mode to "Soft Light".
You can (and should!) improve the look of the edges by various means. I like to apply Gauss filters with different settings a couple of times to smooth the transition, I also like to give the edges some detail by applying my most beloved Noise-filter. You can also change the highlight by using a soft eraser tool to decrease the effect for the matte materials (leather, plastic, etc). I don't want to go into detail about that here so let's leave it and just move on.
Step 4 - the dark side!
Assuming you work with low-tech modelling programs like Gmax, you don't have the chance of "baking" a shadow layer to your texture. Therefore, in order to give your part some depth you have to draw the shadows manually. This can be a very tedious work if you want it to look right. For now we just create a rough draft.
Create a new layer and set the blending mode to "Hard Light". Take a smooth brush, set the opacity to about 20-30% and start drawing the shadows wherever you feel like it. Eventually you'll end up with something like this:
Again, you can further improve the looks by applying a noise filter.
Before we continue with the tutorial I want to give you a rough idea what we want to accomplish here. When I started with 3d modelling and texturing a couple of years ago, I basically used photographs of the objects I modeled for the textures. And when I look at some of the aircrafts around - no matter if it's payware or freeware - this technique seems to be widely used. But in order to achieve a good result, you have to find or take a good photograph of your part. This research takes a lot of time and even if you got good photographs of your object you still have to adept the image for you texture. E.g. stretch it, clone-stamp it, match the colors for the edges, etcetc. In other words you spend a lot of time for research and post processing.
When I first started with the Electra I used a different approach. I basically tried to replicate the look of the real-world part using a lot of filters in photoshop. My instrument-background-tutorial is a good example for this technique. Following this philosophy you can save a lot of time and you don't need these high-resolution photographs anymore. On the downside it is most likely that your parts will have a Mickey-Mouse-style and the reason for that is that it is almost impossible to replicate the fine nuances of a real-world material manually.
The solution to this dilemma is a mixture of both approaches. The basic idea is to create all the decals, lettering, shadows, edges, etc. manually and then use a some photograph of an appropriate real-world material to give the texture more detail.
To make this happen you need a good library of generic material. One way to take your camera, go outside and take photographs of plain materials. If you like photography feel free to do so. But I am a really bad photographer, so I prefer the lazy approach. You'll find a lot of good texture libraries on the web. My favorite one is www.cgtextures.com (Danke Sandra! *schmatz*) where you can choose your photos from a huge database - all free of charge. My advice is to start building up your image library and constantly add to it.
Step 5 - even more magic!
Let's open one of these bare-metal textures. It doesn't really matter which one you choose, just pick one that shows the details you are looking for. Have a couple of these textures ready for every detail you want to see. Do you want to have scratches, corrosion/rust, exfoliated paint? Look specifically for these features when choosing your texture. Also look for the lighting. Most of the time you want to have a photograph of a homogenous material with few highlights. Sometimes such highlights and shadows can bring even more depth into your texture. I really like this one and use it all the time for all bare-metal parts in my airplanes:
Copy the image (or parts of it) and paste it to our wip texture. Adjust the size of it to get as much detail as possible. Sometimes you might want to use the "Sharpen" filter to make it more crisp.
And now change the blending mode to "Overlay" and be surprised!
With this one simple step you really enhanced the look of your texture. By using a real world photography you've got all the fine nuances that were lacking in the Mickey-Mouse-version and yet you preserve the detail of your hand-drawn texture.
On the other hand you don't have to spend a lot of time searching for the perfect photograph because pretty much every generic photo of a somewhat-alike-material will do the job!
With this tutorial you've learned two very powerful methods to increase the quality of all your textures. By highlighting the edges of your 3d parts with the texture you are helping the 3d illusion. Using blending modes to blend in real world materials help you to get rid of the Cartoonist look by adding more detail to your part.
I suggest that you spend some time experimenting with blending modes to find out what's looking good and what doesn't work. Using Overlay is always a good start, but if you want to use multiple materials you will find other modes better. As an example: When I want to have some more scratches on my material, I am often using a "Hard Light" blending mode with a heavily scratched texture and make use of a soft eraser tool to remove some of the scratches where I don't want them. The "Hard Light" setting will give you very crisp edges around the scratches while disregarding the rest of the texture. Try it!
I also want to highly encourage you to share your experiences with these techniques. I'd love to see some pictures of your implementation of the methods!
Please feel free to comment on the tutorial or ask questions if I didn't made a step clear enough.
--Vitus 20:47, 6 August 2011 (EDT)