Loss of texture detail in XNA (Banding 16 bit issue)

Question

I'm loading in a background texture for my game, it's not vert detailed, it's just there too add some variance. The problem is that there looks like a large reduction in detail. I've included images below so you can see what I'm talking about. What would cause this to happen and how can I get my detail back?

More info:
Verticies are VertexPositionTexture
Load method Texture2D.FromStream
Effect BasicEffect

Also the project is a Silverlight/XNA mix

Source Image:

Image from game:

Note: the images don't match up completely but you should get the idea.

Answer 1

Your texture is a 32 bit texture. Somewhere between loading it and displaying it, it is getting downsampled to 16-bits (or some other low bit-depth). The loss of precision gets rid of the smooth gradients and gives you bands of colour like that.

None of the things you have mentioned (loading it with LoadStream, drawing it with BasicEffect with that vertex format) will reduce precision like that.

My bet is that you're rendering to a 16-bit backbuffer. I can get a similar result by setting:

graphics.PreferredBackBufferFormat = SurfaceFormat.Bgr565;
graphics.IsFullScreen = true;

You can verify your actual backbuffer format (note that what you specify to GraphicsDeviceManager is just a preference) by checking:

GraphicsDevice.PresentationParameters.BackBufferFormat

It's also possible you're using a low-precision render target somewhere.

Answer 2

By default, in Windows Phone 7 all apps use 16 bits per pixel graphic mode. To switch it to 32 bits, see here: http://stackoverflow.com/a/10313783/126995. This is only available since WP 7.1 Mango, but since every WP7 device can be upgraded to WP 7.1, it's no big deal.