Using GIMP: Correcting and Touching Up Your Images - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 61

Interpolation
Interpolation defines how the image dots should be recalculated when you
save the final image.
The default is AHD interpolation . It provides the best results but may
enhance the noise in the photo.
VNG interpolation provides very good results.
VNG four color interpolation should be used if you find Bayer pattern
artifacts in your photo (for other disturbing patterns, see section 2.4.3 and
2.5.7).
PPG interpolation is short for Patterned Pixel Grouping interpolation. This
interpolation method is nearly as good as the previously mentioned methods,
but it's much quicker.
Bilinear interpolation is a very basic interpolation, but it is fast.
After the interpolation, you can apply the color smoothing function by
clicking on the brush icon. Color smoothing can help reduce color artifacts
such as pixel noise and blemishes without losing any details.
Figure 2.6
An image that was saved and reloaded
shows a disturbing colored grid
pattern, commonly known as Bayer
pattern artifacts.