Why is the size in pixels wrong in Aperture?

If you open a RAW file in Aperture and compare the size of the picture with another application, it is very possible that the size is different.

This is not a bug. In contrast to tiff or jpeg, RAW files do not necessarily have the exact number of pixels defined, but small variations can take place.

I did some tests on one particular nef file from a Nikon D300.

First I converted the file to DNG, so I could open it in Photoshop CS2.

I then opened both DNG and NEF in the gimp with UCRaw. Result for both files: 4320*2868 pixels.

I then opened both DNG and NEF in Aperture. Result for both: 4304*2852 pixels.

I then opened the NEF in Capture NX. Result: 4288*2848 pixels.

And finally I opened the DNG in Adobe Camera Raw and Photoshop. Result: 4288*2848 pixels.

As you can see, out of four unrelated applications with different development teams, only two agreed on the number of pixels. And the applications that agreed, opened two different files (the dng and the nef).