Desktop wallpaper strangeness

I downloaded some 1440x900 images to use as wallpaper.

In aperture, the full size view looks great and fills the screen.

When I set them to my wallpaper via system preferences, the images seem to shrink somehow, such that I have to set them to 'stretch'. The resulting wallpaper looks low quality.

How can that be???

:edit: if I first export to my pictures folder, they work fine. must be to do with aperture.

 

The choices are Fit to Screen, Fill Screen, Stretch to Fill Screen, Center and Tile. I suspect if you hit Fill Screen and it's 1440x900, if you're on a 1280x800 screen, it would shrink the 1440 dimension and in order to preserve aspect ratio the image would normally be as tall as the screen but would wind up being 750 pixels tall. Is your native resolution 1200x800? If so, try picking " stretch to fill screen" or " center" rather than "fill screen".

Using Aperture, or in my case Gimp, it is possible to stretch or crop an image to be exactly your screen resolution (and save it as a new image of course). To me this is the best way as it eliminates any mistakes and even if you picked tile or center, the image should fit your screen.

 

Thanks but that's not it. The images look fine if I first export them to a folder. And I am on a MBP so 1440x900 is native...

When I hit 'centre' with an image referenced from Aperture... it only fills up half the screen. If I export the same image the 'centre' view is just right.

It is defo some aperture wierdness