How Digital is Digital?17 Feb, 2002 By: Jim Intravia imageSource
How Digital is Digital?
digital copier is really cool. I love SO/PM. I think it is so wild to put an
original away while the copies are still pumping out. I think it is great that
the machine can collate without a collator. I find it practically amazing that
some machines will put the image squarely on the paper, even if the original is
turned 90 degrees on the glass, or placed in the wrong corner of the glass.
Being able to duplex all day long without being limited to 50 sheets is
get a kick out of the fact that a tiny amount of dust in the exposure optics
might cause a gray line on a digital copier. It still seems funny that a dirty
slit glass will give a light copy instead of a dark one.
above are all functions of a digital copier that do not apply to analog. I'm
guessing that in about two years, we will stop saying digital. It will be
assumed. We will still say analog, when it applies, only because we must
differentiate for certain reasons, especially for technicians learning the
a copier is digital, it can so/pm (scan once, print multiples), rotate the
image, store copy jobs in memory to allow collating and duplexing without as
many moving parts, and, depending on the model, do some other fancy things.
However, the main thing that it has to do is make copies. We know that digital
devices generally reproduce things better than analog devices. Digital answering
machines are better than tape machines. Digital phones give better sound
quality. CDs give better tones than records and cassettes. DVD is better than
VHS, and so on.
Is Better, Right?
It stands to reason that a digital copy is better than an analog copy for the
same reasons, right? Wrong. I have seen it said that digital copiers “create
originals.” Not really true, unless they are being used as printers. When an
image on a computer screen or on a disk is sent to the laser, it is a purely
digital image. The image on the screen is analog only to the human eye. From the
screen to the laser it is digital. Nothing but 1s and 0s. That is a true
original. There is no optical distortion; no bending, twisting, vibrating or
anything else to interfere with the image. The image will reproduce perfectly.
a digital copy is not a print and is not a purely digital image. It is, for the
most part, analog. Here is why:
In an analog copier, here are the steps for reproducing the image:
Original document is scanned through the platen glass (approximately eighth of
an inch of glass causing some slight distortion and loss of light energy).
2. Reflection of original is
bounced to first mirror (some light diffusion and loss of light energy) to
second mirror (more light diffusion and energy loss) to third mirror (more light
diffusion and energy loss).
3. Image is sent to a “through
lens” (about 1/2 inch of glass, with some distortion and loss of light
energy). This image then usually strikes another mirror, or maybe several,
before it goes through a slit glass and is eventually reflected onto the drum
the most part, even with a magnifying glass, you have trouble identifying which
is the original and which is the copy. Most of the light diffusion, light loss,
energy loss, and distortion has been engineered out of copiers. To the (analog)
human eye, the copy is just as good as the original (if the original is the
correct type for good copying). No part of the analog xerographic process can be
described as digital, other than the fact that everything is made up of
In a digital copier, here are the steps for reproducing the image:
Original document is scanned through the platen glass (approximately eight of an
inch of glass causing some slight distortion and loss of light energy).
2. Reflection of original is bounced to first mirror (some light diffusion and
loss of light energy) to second mirror (more light diffusion and energy loss).
3. Image from the second mirror is sent to a “through lens” (about half inch
of glass, with some distortion and loss of light energy).
4. Image from the lens strikes the surface of the CCD. At this point, it becomes
5. Digital pulses travel by wires to the copier's circuit boards and are
directed to turn on the laser beam at the appropriate times.
6. The laser beam (an analog device) is fired to the rotating (analog) polygon
mirror, which reflects the various areas of light and dark to a mirror or two
and through a slit glass onto the rotating drum, creating an analog image.
a digital copier, the only digital events take place in steps 4 and 5.
Everything up until the CCD converts the image to 1s and 0s is analog. After the
1s and 0s are converted to an optical image, it is analog again. In reality, the
copy is analog. Images created by 1s and 0s are not digital if they are capable
of being analogically (new word?) altered in normal use. Consider all the
following: speed and imperfection of the rotating polygon motor, the
existence of the mirrors in the laser unit, the slit glass, light diffusion
caused by floating toner particles or dust, the rotation of the drum. These are
all analog effects, which can slightly change the characteristics of a 1 or a 0.
all practical purposes, there is no difference between the copy quality of an
analog copier or a digital copier. If second, third, fourth etc. generation
copies are produced from an original, each has an advantage in certain
situations. For the most part, however, a machine in perfect condition will make
a perfect copy, as far as the human eye is concerned, regardless of whether it
is analog or digital. About the only time this matters is in certain sales
situations. If you are selling an analog machine (more likely a used analog
machine from this point forward), you should be prepared for this argument. On
the other hand, if you are promoting digital and have to counter this argument,
you should be prepared to talk about the other advantages of digital.
As my father used to say “six of one, half a dozen of the other.” In this
business, and probably in every business, it is not always what is true, but
what people think is true that matters most.