Bicubic Resizing vs Bilinear
Everyone uses Bicubic resizing religiously when
they make DivX movies or any time they resize pictures in photo
editing software. I have suggested that it is best to use Bilinear
to shrink images and Bicubic to enlarge them. In fact I believe
it is a rule that shouldn't be broken. But then again there is
mixed opinion even among experts on this matter. Digital photo
experts JASC (makers of Paint Shop Pro) comment: "Use the
Bilinear Resampling method for shrinking these images and Bicubic
for enlarging them". Whereas the help file of Adobe Photoshop
just mentions that Bicubic is more exact method for resizing.
In actual fact Bicubic is more precise, but only
when it comes to enlarging. When it comes to shrinking its exactness
can actually produces pixelation, because to shrink an image pixels
must be discarded anyway.
The following shows examples demonstrating this
effect. There are reasons you may prefer Bicubic shrinking methods
though. Namely, if sharpness is absolutely vital and pixelation
problems are less important.
The following is the effects of enlarging a
small image using Bilinear Upsizing.
Notice how blocky the image appears
Next demonstrates the effects of enlarging
using Bicubic Upsizing
Notice how smooth the image appears
The following demonstrates the effects of shrinking
using Bicubic Downsizing:
Notice especially the hair where hard pixels
Finally the following demonstrates Bilinear
Notice the hair again, the pixels have been
anti-aliased to produce smooth lines.