The basics

Image capture – input resolution
ADVANCED PHOTOSHOP ELEMENTS 5.0 FOR DIGITAL PHOTOGRAPHERS
Computers can only work with digital fi les. The world as we view it, and as we capture it in
silver-based photographs, is not in a digital format. Tones and colors merge gradually from one
extreme to another. For the computer to be able to work with such images they must be changed
from this 'analog' or continuous tone format to a digital one. Scanners and digital cameras make
this change as part of the capturing process.
The scene or print is tested, or sampled, at regular intervals and a specifi c color and brightness
allocated for each sample area. The testing continues in a grid pattern all over the scene,
gradually building a pattern of the image which is made up of discrete areas of specifi c color/
brightness. Each of these areas, or samples, becomes a pixel in the resultant digital fi le.
Resolution at this capturing stage refers to the frequency that samples are made of the image.
Generally this measurement is represented as the number of samples taken in a one inch space;
for this reason it is sometimes called Samples Per Inch or spi. Unfortunately most scanner
software does not use this terminology but prefers to refer to this setting as 'Dots Per Inch' (dpi).
This is a hangover from language used in the printing industry and does more to confuse than
clarify the situation.
If you are using a digital camera to capture your image then the resolution will be determined by
the sensor, which has a specifi c number of CCDs set into a grid that is used to digitize the image.
Scanner users, on the other hand, are able to control the sampling rate by changing the settings
in the scanner's dialog box.
A high sampling rate will result in a higher quality image with a much greater fi le size. A low
SPI will provide a smaller fi le of less quality. These facts lead a lot of new users to a situation
where all images are scanned at the highest resolution possible. Do this and your hard drive will
soon be completely used up. High-resolution scans require huge amounts of storage space.
Input resolution >> High input resolution (a) will produce an
image with fi ner detail than a picture with low resolution (b).
Book resources at: www.adv-elements.com
15
SCANNER AND
CAMERA TECHNIQUES