|Discussion of the Term Resolution The term Resolution has
various meanings depending upon the context in which it is used.
This article will use scanners as input devices to illustrate
different types of resolution. First, I will discuss raster images
and resolution. A scanner takes an "electronic picture" of an
image. The image can be reflective (paper) or transparent (film).
Since this is a type of picture, it captures the image in bitmap or
raster form. This form means that the output image is made up of
pixels the same pixels viewed in Photoshop or Paint Shop Pro.
Each pixel has a color depth. Usually one decides on how the image
will be used, and then, on what output resolution is necessary.
There used to be different output numbers such as 300, 200, etc. in
manuals. Now, they have been replaced with terms such as good,
better, best. These terms are ambiguous. Normally, if one is
scanning for print and will use the whole image, 300 dots per inch
(dpi) is a good choice. If one is scanning for the web, 72 dpi,
also called screen resolution, is a good choice. Scanners are
constructed employing two types of scanning resolution, hardware
and software. Hardware resolution is the optical resolution. This
means that the resolution is set through the optics of the scanner.
One could call this a "pure" resolution. The other type of
resolution that comes with a scanner or can be bought separately as
a scanning package is software resolution. This starts where
optical resolution leaves off. This type of resolution can be
called interpolation, resampling, or upsampling. I will discuss
this later. Various terms are also thrown around having to do with
image resolution. These are ppi, spi, dpi, etc. ppi and spi - When
scanners first became available to the home user, one could choose
to scan through and specifying an input resolution. The term ppi
means pixels per inch and spi means samples per inch. If one had a
4" x 5" picture, and one wanted an 8" x 10" image at 300 dots per
inch, the input would have had to be 600 ppi or 600 spi, because
the size of the output image would have been doubled. Now we rarely
use that term in that context, and think of output resolution or
dpi, which means dots per inch from printer terminology. Presently,
the size of the input image is not as relevant. On most scanning
devices, one can just put the output resolution desired and the
computer software does the work. If you take a bitmap or raster
image and magnify it, you will see a series of squares. These are
pixels. They contain RGB information. The amount of the information
is called bit-depth.
copied, printed, or reproduced in any manner without written permission from the artist.
Thank you so much for this outstanding article. Resolution can be very confusing, espeically when converting an image from online viewing to printed page. Do you feel that you can re-size an image's resolution from web [72 dpi] to print size [350 dpi] within Photoshop, and get a quality print? Or do you feel that additional software would be better suited for that kind of task? Dee-Marie
To answer your question, it depends on the image. The image size plays a part in it as does its color, its shadow and highlight quality, etc. If you are printing it on an inkjet printer as a relatively small print, probably and it doesn't hurt to try. If you are sending it to a prepress house, I would hesitate to recommend it. I believe that a software program like Genuine Fractals is very good. There are more than one out there and two of them are now ownes by the same company. Genuine Fractals is not owned by Lizard Tech any more.