Digital Photographer's Software Guide - Bertemes - Net

28
Image Rescalers
After their first experience of sending a digital image to a print shop for enlargement
and printing, many people express astonishment at the high image quality
obtained by a professional service. The original image may have been only 8
megapixels, but when it comes back it looks like 16 megapixels or more. How did
the extra resolution come to be there? The answer is through interpolation. This
process runs complex routines that place additional pixels in between the existing
ones, at the same time taking into account the existence of edges and fine detail.
This process is called, colloquially, up-rezzing.
Image rescaling (to give it a more formal name) is a lucrative market for software
developers because so many companies and individuals need to print high-quality
digital images. There has been intense competition to create the best possible
method, using interpolation routines with exotic names like “bilinear,” “bicubic,”
“B-spline,” “sinc,” or “Lanczos.” Broadly, rescaling algorithms fall into “non-adaptive”
types, like those just mentioned, and “adaptive” types, which are much
smarter because they give special attention to edge-defining pixels. If a developer
wants to make an impression with a new brand of rescaling software, it has to be
based on a very fancy adaptive algorithm. A good example is the adaptive S-Spline
XL algorithm in BenVista’s PhotoZoom Pro, but others produce comparable
results, depending on the required magnification.
The price range for image rescaling software is relatively high: $150–$450.
Photoshop and other editors have rescaling facilities, so is an alternative method
worth the extra expense? The answer is absolutely, if you want to print enlargements
beyond 8"×10". All the packages listed in this chapter will make significant
improvements.