Page 143 - Graphic Design and Print Production Fundamentals

Graphic Design 131
nozzle for every image that is produced with an inkjet printer or an electrophotographic engine. This
is what allows us to make every image different and personalize it for the person we are delivering the
image to. It also makes the process slower and less reliable for mass production. The RIP produces a
lower resolution raster grid, so the detail in photos and letter shapes is not as precise. We can have a RIP
discard data if we have too much detail for the raster grid it is producing. The RIP does not do a good
job of interpolating more data to produce additional detail in a photo or graphic shape if that information
is missing to begin with.

That brings us to examining the resources that a RIP must have to produce a perfect raster for every
graphic shape it renders, and for every colour being reproduced. The resource a RIP consumes is data.
In the graphic communications industry, we should all wear T-shirts that say ‘Pigs for data!’ just to
distinguish us from our media colleagues who are producing computer graphics for electronic media. If
we think of a RIP as an auto assembly line we are feeding with parts, in the form of files in different data
formats, it will help us understand how to make a RIP more efficient. If we feed too many parts into the
assembly line, it is easier to throw some parts away than it is to stop and recreate a part that is missing.
If we feed the assembly line with five times as many parts needed to make a car, it is still more efficient
to throw parts away than it is to stop and recreate a missing part.

If we apply this analogy to image resolution, we can point to examples where designers regularly
repurpose images from a web page to use on a book cover or poster print. The web page needs to deliver
the photo across a network quickly and only needs to fill a typical computer screen with enough detail to
represent the photo. A typical photo resolution to do that properly is 72 pixels per inch. Now remember
that the raster grid for a lithographic printing press that will print the book cover is 3,000 lspi. Our RIP
needs much more data than the web page image contains! Most of the photos we are reproducing today
are captured with electronic devices — digital cameras, phones, scanners, or hand-held devices. Most
store the data with some kind of compression to reduce the data the device has to store and transfer.
Those efficiencies stop at the RIP though, as this computational engine has to decompress the data before
applying it to the graphic page it is rasterizing. It is like breaking a steering wheel down to wires, bolts,
and plastic sleeves that efficiently fit into a one-inch-square shipping package, and putting this ‘IKEA
furniture’ steering wheel onto an auto production line for the assembler to deal with in two-point-two
minutes!

On the other hand, we can capture a digital photo at 6,000 pixels per inch (ppi) and use it on a page
scaled to half the original dimension. That is like packing a finished steering wheel in 10 yards of bubble
wrap and setting it on the assembly line in a wooden shipping crate! So it is important for designers to
pay attention to the resolution of the final imaging device to determine the resolution that the RIP will
produce from the graphic files it is processing.

Halftone Screening

It is important to stop here for a discussion about halftone screening that a RIP applies to photographs
and graphics to represent grey levels or tonal values in a graphic element. We described how the RIP
makes a grid of one-bit data, but graphics are not just black and white — they have tonal values from
0% (nothing) printing to 100% (solid) printing. If we want to render the tonal values in-between in half
percent increments, we need 200 addresses to record the different values. Computer data is recorded in
bits, two values (on and off), and bytes, which are eight bits strung together in one switch. The number