Size differences between UV Maps

I found something really odd today, which I haven't noticed before.

Using both the upper and lower UV maps in separate psds, I copied a button from the upper to the lower. However, when rendered in SL the button on the lower item was noticeably larger than the one on the upper item. Checking both tgas, the buttons are exactly the same size.

Not sure if it's just me or not. If not, is there some standard magic shrinking formula that can be applied to lower textures to keep them in scale with the upper?

There is no magic formula that will gain you an exact ratio unless you perform a calculation on each polygon. I can tell you from personal experience that the general ratio towards the middle area of tha avatar at the waist line is about 1.3-1.2 to 1 from upper to lower.

You significantly reduce this issue using a 3D application to paint or project the texture onto. The 3D application will calculate the amount of texture distortion needed to traverse each seam and polygon at the correct ratio.

Thanks for the explanation, at least it's not something I did by mistake. I've come to appreciate the difficulties of working around certain parts of the avatar, but wasn't prepared for so great a scale difference between supposed adjacent areas.

Welcome to the joys of texturing the SL avatar, hehe. To make matters even more difficult, the size ratio varies by individual polygon, not just between the various parts of the template, especially the polys near the sides of the avatar at the waist seams. You can get a general sense of the differences in resolution between template parts by assigning a checkboard texture to all three skin slots, then take screenshots of your avatar and compare the size of the checks. That will give you a general ratio to work from. You'll still need to do a fair amount of tweaking depending on what part of the av you're working on.

Just a question.. can you recommend a program for painting onto a 3D Model? Someone suggested 3D Max? I'm looking into getting a program that works with my wacom tablet intutively and doesn't run chunky or blotchy like some of the freebees I've tried.
Basically i'm willing to spend what ever is needed to be able to fine tune my textures on 3D models.

Any suggestions?

3ds Max doesn't have 3d paint natively, but there's a great plugin that connects 3ds and Photoshop, allowing you to use Photoshop's tools directly on models in Max. It's around $395 but you'd need PS and Max already, and they're both very expensive.

Less expensive solutions include Zbrush, BodyPaint, Deep Paint 3D, and Modo.