Digital Prints

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Mastering Digital Printing
Cheating Pixels
When you’re stuck with a given resolution of an image, but you want to blow it up and
print it big, Photoshop’s Bicubic Resampling function does a fair job—up to a point. It
creates interpolated pixels in an attempt to trick your eyes into seeing more detail than is
actually there. However, the image soon begins to break down as you increase the enlargement.
There are several software products that try to improve on the basic Photoshop interpolation
method; each has its own group of believers. Here are three:
FM Stair Interpolation: Photographer Fred Miranda used to offer a Photoshop action
(automated series of commands) that broke Photoshop’s Bicubic interpolation method
into small steps, which is why it was called Stair Interpolation or SI. At this writing,
Miranda had replaced all the older versions with Stair Interpolation Pro, a Photoshop plugin
(supporting 16-bit in CS) for PC and Mac that has options to interpolate images based
on either paper size, pixel dimension, printer resolution, or scale. SI Pro is available via
download (www.fredmiranda.com) for a nominal fee and works with all digital image files.
(Photographer Glenn Mitchell offers a free version of his TLR ImageResizer for
Photoshop as an action set for enlarging in small increments. Downloadable from
www.thelightsright.com)
Genuine Fractals: LizardTech’s Genuine Fractals (GF) is a Photoshop plug-in that enlarges
images using proprietary fractal technology. You first encode the image in GF’s.STN format
and save it with a choice of Lossless compression (2:1 savings) or Visually Lossless
(5:1 savings). You then enlarge it: 150 percent, 250 percent, or more. The PrintPro version
supports all Photoshop color modes including RGB, CMYK, and CIE-Lab, and it
encodes and renders 8- and 16-bit images. How well GF works depends on the to-from
file size and the type and quality of the image involved. For Windows and Mac.
Qimage: Qimage, the stand-alone image-editing and printing software, has nine different
interpolation algorithms (including Lanczos, Vector, and Pyramid) to “res up” images.
Many users feel that Qimage’s interpolation methods are better than those used in most
image editors for making large prints from small files.
Qimage developer Mike Chaney explains the differences among the main interpolation
functions. “Most interpolation methods including Bicubic and Lanczos use a ‘windowed’
function to look at pixels in a square window, say 7 × 7 pixels. The interpolated pixel’s
value is computed using mathematical functions that apply a weight to each of the pixels
in the window. The function itself is what determines how much weight each pixel contributes
to the final interpolated (target) pixel, and therefore what the final image will look
like. Bicubic usually produces smoother results, but less sharp, while the Lanczos function
produces sharper results because it uses the mathematical sin function, which has a natural
tendency to sharpen edges due to its repetitive or ‘cycling’ nature. Vector is a different
kind of function that looks at geometric shapes produced by pixels and interpolates by
looking at the target pixel’s position inside a plane formed by several adjacent pixels in the
source/original image. Pyramid is a complex extension of the vector algorithm. It basically
refines the vector approach by considering many more complex shapes when creating the
planes and doing the geometric placement of pixels.