Any ideas how one can generate a smooth dark graduated background within AE ?
I'm using a CS4 16 bit project and have tried 4 colour filter, feathered solids, 3d lights and even a friends copy of CS5 but always end up with quantising/ banding.
I'm bringing in one made in Photoshop and it's displaying fine - but not flexible enough to satisfy me.
Strange - 4 color gradient in a 16 bit comp should give you smooth gradients. It may be the way your display shows it- but then you mentioned that a PSD gradient looks fine. Try rendering out a few frames and look at it in a player to see how that looks.
Are you looking at it with a 10-bit monitor? If not your gradient is going to band once it hits a certain size (like 256 pixels f/ full greyscale white to black). That doesn't mean the comp is banding, it just means your display is. And everyone who looks at it on an srgb 8-bit display or worse (most lcds are 6-bit) will see it banding as well. In fact even a 10-bit display should band in certain circumstances (> 1024 pixels of full greyscale ramp).
To minimize it:
You can add grain.
You can also add an adjustment layer with the 4-color gradient, use the 'color' transfer mode (or any really) with a very low opacity. All of those will give your display more colors to work with to reduce banding.
Even on a 6-bit or 8-bit display, you should still work in a 16-bit or higher project as you are when addressing this issue.