Re: Manual photography versus digital

uraniumcommittee@xxxxxxxxx wrote:
This thread has gone on far too long.

Obviously *not*, given that people are still interested in
learning what "digital" and "analog" actually mean.

But I do notice that you *are* trying to post a *real* answer,
rather than your usual nothing-but-troll idiocy. Seems that
this thread got to you...

Image capture is not 'digital' in a so-called 'digital' camera.Capture
is electronic. Brightness is represented by signal strength at output.
The image is STORED in a digital electronic format.

Astounding! You posted three correct, non-troll, statements in a row!

Printing is
accomplished by any number of means, none of which is 'digital'.

Opps. In fact the display, whether on an monitor
screen or printed on paper, outputs what is called
"quasi-analog". It is effectively analog in that it registers
on our analog sensors (in this case the eyes), but in fact it
is made up of a finite set of discrete values, which is digital
by definition. (In the case of a CRT monitor, the monitor is
where that conversion takes place, rather than our eyes. The
CRT monitor is actually an analog output device.) Printers of
course print dots. Even the color of the dots is determined by
a finite set of values rather than any continuously variable
set.

But our eyes perceive it as analog.

Film is chemical capture and analogue storage. Film could be used to
record digital images, just as tape or discs are, but optically instead
of chemically.

It could be "optically" or "chemically".

Motion-picture soundtracks are either optical or
magnetic analogue, recorded right on the film. The head is either like
that of a tape recorder or an optical light beam. The recording is
analgue in both cases, although some new systems use a digital
synchronized disc separate from the film (Sony DTS).

Excellent point.

William Graham wrote:
"Floyd Davidson" <floyd@xxxxxxxxxx> wrote:
....
Digital is discrete *by* *definition*.
....

Consider a binary digital system using voltage. It would have
exactly two values (1 and 0). We might define any voltage
greater than 1/2 volt as a 1 and any voltage less than that as a
0. The *voltage* is clearly analog (there are an infinite
number of voltages between 0 and 1 volt and the voltage is
continuously variable between any of them). But our information
is a digital transmission system, with digital data carried by a
digital signal. That is because we have defined it to have
exactly two values, 1 and 0. There is no value of 1/2, no
matter what the voltage may be.

If the above digital data happens to be transmitting or storing
an image, we might note that if the voltage varies between 0 and
1/4 of a volt it will *not* change the image.

On the other hand, if it were an analog system with a maximum
value of 1 volt, a variation between 0 and 1/4 volt would be
visible in the image.

Change the use of "voltage" above to be *any* characteristic
that can be varied, and the exact same difference between analog
and digital will be true. That is true of magnetic fields,
silver grains, voltages, electrons, photons, or whatever.

I have been following this discussion, and I believe there is another
characteristic that makes an image "digital", as opposed to a film image.

There is a distinct difference between what *defines* digital
and what is a *descriptive* *characteristic* of using a digital
system. We've been discussing what is defined as digital,
trying to separate that from how people more or less relate to
the characteristics of digital systems.

For that reason I want to be clear that the following relates
*only* to the resulting characteristics that follow from using a
digital system, and does not discuss what defines that system as
digital. (Two distinct topics, and both of them are very useful
to understand.)

Random noise is a natural part of a film image, and this noise is
indistinguishable from real data. But in the digitized image, each "pixel"
must conform to some protocol, or coding method, and a random bit will very
likely be interpreted as an error in the data by the reading and
interpreting program, so the image will not deteriorate over time in the
same way that the analog image does.

This is an excellent point! Let me state it a little different.
An analog system is prone to errors from noise. The noise, even
when very small, is additive and accumulates, which eventually
can and will greatly interfere with the data. Each small amount
of noise adds errors to the data, which can then never be
removed.

Hence an image stored or transmitted via an analog system is
damaged by the errors resulting from noise within the system.
An example would be that if we find a box of slides from 40
years ago and try to print them, the prints will not be as good
those we would have printed 39 years ago. Likewise if we find a
print made 39 years ago, we can't really copy that perfectly
either. Fading, scratches, fungus, etc etc will all take a
toll...

But a digital system is error free despite the noise. I.e., for
any signal-to-noise ratio above a certain minimum (which happens
to be relatively lower than would be reasonable in an analog
system) the error rate is zero. The noise is not accumulated
(the signal can be perfectly regenerated without introduction of
errors).

Hence 40 years from now it will be possible to print an image
from digital data that will be *exactly* the same as one we
print today. As long as the noise in the system remains below
the threshold that causes errors, the error rate will be zero.

The fact that film has grain, and this
grain is comparable to the pixels in a digital image does not make them both
the same thing. The pixels in the digital image are ordered, and must
conform to some code. This is not true of the grain in film, which is
entirely without any "order" and can run the whole spectrum of random noise
from perfectly white, to pure black, and anything in between.

Exactly! (And that last bit does touch on definitions...)

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) floyd@xxxxxxxxxx
.

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