Now the correct image is loaded (Fig.39).
Repeat this for the Bump Channel and load in the SlimyMetal_bump.jpg.
Once you're done, go back to the top level of the material, this is what you should now have (Fig.40).
Now we have a specific image for each specific channel. Let's render (Fig.41).
Might not seem better, but it is; we will need some further tweaking of amounts to really see the difference (Fig.42).
And here are the same amounts applied to the material with just one image for all three channels (Fig.43).
I hope by this point that you can see and understand why it really does make a difference when you make specific images for specific channels.
Each channel has a different purpose so treating them as such is the trick to generating better and more realistic materials.
If you look at the render in Fig.42, I really want you to notice how where we see the green moss on the surface, we don't really see any specularity. This is very true to real life: impossible to get without creating and using specific maps.
More Map Types
Let's continue experimenting with some of the other map channels so you get a feel for what they do.
Save this image as SlimyMetal_spec_color.jpg (Fig.44).
Now, using the same technique as before, copy one of the bitmaps from any of the three channels we are already using and replace that current bitmap image with this one. Here's what you should get from the render (Fig.45).
Now we can control what colour shows up in the Specular channel.
On to the Self illumination channel. Go ahead and save this image as SlimyMetal_selfIllum.jpg (Fig.46).