CHAPTER 12 THE IMPORTANCE OF RESOLUTION 189Converting pixels in a digital image to dots that make up the screen requires a
device known as a RIP (Raster Image Processor). You might have seen one of these
devices next to a color laser printer at your office, or even at Kinko’s.
Imagesetters, which are used to make the plates that go in printing presses, can only
create one size of dot. However, if you combine the dots to make larger ones, you
can create these continuous tones.
A halftone dot is created from a grid of laser spots known as a halftone cell. The
greater the number of cells filled with spots, the larger the halftone dot will appear,
and the darker the dot will seem.
The human eye cannot distinguish dots from a distance if the dots are small
enough. Because printing presses cannot create continuous tones (like a dye-subli-
mation printer), trickery must be employed to create the perception of a continuous
tone. If you vary the size of dots across a grid of dots, and if the dots are small
enough, the eye will see only a gradation, not separate dots.The Absolute Minimum
An accurate understanding of resolution is difficult even for experienced photogra-
phers. Wade through the terms and differences among hardware devices and you
might find yourself thoroughly confused. Experiment with scanning, printing, and
onscreen editing to understand how images flow through the chain of resolution.
The following tips might help, as well:
■ Digital cameras capture images at 72 pixels per inch. You need to change
this resolution prior to printing.
■ Disposable cameras have about the same resolution as a 3-megapixel
camera.
■ Because of scanner limitations, 35mm slides taken with the highest quality
optics contain as much resolution as an equivalent 20-megapixel sensor.
■ The common accepted term for input resolution is pixels-per-inch (ppi).
■ The common, accepted term for printer resolution is dots per inch (dpi).
■ Most digital cameras capture at 8 bits per color (24-bit) resolution. High-end
SLRs can capture at higher 12-bit and 14-bit resolution in RAW mode.
■ Editing in Photoshop and Photoshop Elements is done at 8-bits per pixel reso-
lution. Only a few editing options are available at 16-bits per pixel.
■ Most professionals scan negatives and slides at 48-bit resolution (16 bits per
pixel), which must be converted to 8 bits per pixel after importing into
Photoshop and Photoshop Elements.