[size=200:1ri27dey][b:1ri27dey]Towards A Sim Builder's Guide To Textures[/b:1ri27dey][/size:1ri27dey]
[b:1ri27dey]What is a Texture?[/b:1ri27dey]
Textures are just images (think JPEGs) that your Second Life client program uses when it draws objects. Your program displays these images at an angle attached to the surface of primitive shapes (prims).
[b:1ri27dey]Can textures influence lag?[/b:1ri27dey]
Textures require downloading into your computer before the Second Life client can use them to draw the 3D shapes of the Second Life world on to your screen. The downloading process takes time, and this can contribute greatly to the lag you experience as you walk around a sim.
Most textures are kept on the Second Life asset server. When your Second Life program receives 3D shapes from the sim they include an identifier for each texture that is used. The client orders a copy of every texture that it does not have already stored in a temporary storage place (a cache). Before your program downloads a texture, you will notice an object as grey, or as the "missing picture" pattern until the texture is located and downloaded.
Textures can also be stored in the computer that runs the sim. This generally happens when you upload the image for the texture while in the sim. Since the central assert servers tend to be a bit overloaded these days, its often faster to get textures from the local computer.
Smaller textures download more quickly than larger textures. In fact a 512 x 512 texture is four times the size of a 256 x 256 texture. There is a trade-off between size and the number of pixels though, so somewhat larger textures can improve the look of an object. Its a trade-off.
[b:1ri27dey]Why have a texture bank?[/b:1ri27dey]
One of the things that Moon had us do for Colonia Nova was to create a pool of shared textures that could be used again and again. If you re-use a texture it is just downloaded once and so lag is reduced.
I tend to be slightly less than pure on this point. Networks are faster these days. Nevertheless it is a very good idea to have many of the textures in a sim come from a shared pool.
[b:1ri27dey]Where do I find textures?[/b:1ri27dey]
A lot of us who have been building for a while have huge collections of textures. (Mine right now is 1.8 MB, and I would bet that Sudane and Moon have several times that.) If you are looking for something in particular its a good idea to ask one of us.
Textures are available both from free sources and as bought packages of textures. (I have lots from both kinds of sources.) Bought textures have licenses that may limit their use by other people.
My favorite place to find textures is Wikimedia Commons (URL below). This is the image database used for all the articles in Wikipedia, and it has some amazing things in it. Commons is sort of the museum shop of free texture sites. Please be careful to read about the copyright status of each item, because some things do not allow use in Second Life.
A few free texture sites:
http://commons.wikimedia.org
http://mayang.com/textures
http://www.imageafter.com
[b:1ri27dey]What is this "Alpha" thing?[/b:1ri27dey]
Generally an image mixes three "channels" red, green, and blue at different intensities to make all the shades and colors you see on the screen. Every pixel has a number that has a red, green, and blue number that specifies how much of each color that pixel will show. Black is [red=0, green=0, blue=0]. Pure white is [red=255, green=255, blue=255].
There is a fourth number, the alpha number stored with each pixel. It defines how transparent or opaque that pixel is. When a color is opaque it completely masks the color behind it. When a color is, say 50% transparent it is mixed in equal parts with the color behind it.
When it gets to a texture you can think of alpha as being a kind of transparency paint. You can use the alpha channel to make part of an prim transparent or translucent. Most of the windows in NFS work this way, They do not require additional prims because the window's transparency is made using the alpha levels.
[b:1ri27dey]How do I get serious about all this?[/b:1ri27dey]
The main thing is to find a good image program and learn to use it. Many people with Windows computers use Paint Shop Pro. Mac and Windows users can use Photoshop. I tend to use a drawing program to design textures and then use Photoshop to create the alpha channels and touch them up. I also use GraphicConverter to scale images -- it has by far the best scaling algorithm I have found.