I'm totaly new to making my own gauges, so forgive me if I'm asking ignorent questions...

 

I used Photoshop to make new graphics for an exsisting xml gauge and everything works fine, except for a difference in how the graphics of the background worked out. The background texture, consisting of the backplate, rim and lettering, has two parts, the rim and the lettering, that show exactly the same as I created them in Photoshop, but the backplate, however, does not.

 

The backplate is darker at the edges than it is in the middle and in Photoshop this difference in color instensity is a very smooth and gradual transition. In P3D this is not the case and there are rings of color with very grainy edges, that get a step lighter in color the closer they get to the centre. (for the FSX guys, this is in P3D, using 24-bit textures, so it's not the difference between 24-bit in Photoshop, converted to 8-bit before being loaded in the sim...)

 

Is this just the way those textures work in P3D and do I have to settle for this effect, no matter how I build or program the textures? Or is this a setting I can adjust to make the backplate's color transition look as smooth as it does in Photoshop?

Yeah... don't think P3D uses 24-bit textures. Gauges are still using 8-bit graphics.

The effect you are describing is called "gradient banding."
 
Best results would be to apply some dithering to smooth out the gradient banding effect.
 
If you cannot dither, then try adding a layer of noise to your background to help break up the sharp "edges" of the gradient.
 
Here is a link describing these and some additional methods:
http://www.iceflowstudios.com/2013/tips/smooth-gradients-in-photoshop-dithering/

 

Also, convert your bitmap to 8bit for use in the gauge.
 

Because the explination in the FSX SDK mentioned 8-bit, I started with that, but the textures didnt show up in the sim. When I searched for more info I read they had to be 24-bit and when I used those, it worked fine...

 

Thanks for the info, I'm gonna have a look at it

In Photoshop you want to design it as an RGB image... when it's ready, you want to convert the output to an indexed image.