Amiga Collections: MegaDisc/MegaDisc 08 (1988)(MegaDisc Digital Publishing)(AU)[WB].zip/MegaDisc 08 (1988)(MegaDisc Digital Publishing)(AU)[WB].adf/ARTGALLERY/About_Digitising

Text File | 1988-05-28 | 12KB | 237 lines

                        D I G I V I E W  H I N T S

Version 1.0 September 1988                              . . . .Bob Downs

         [Ed: Anyone interested in digitising should read this article
         by Bob, who's really giving us the benefit of his long experience
         here. Bob's put together a number of disks of his digitised
         images, available from him or us. He'll also undertake commissions
         if required - ask him. The "Digi_Dance.pic" is his of course.]

This article is released in the Public Domain on the proviso that it
remains intact and is not used for commercial gain.

Considering the power of Digiview it is probably one of the  most
straightforward programmes to use. Yet without exception all users have
difficulty producing quality results. This article will show you what hard-
ware will be required and how to set it up. To get the most out of the
programme will require practice, and plenty of it!

This manual was originally intended to be "The Definitive Article," but
with product upgrades and continuing R & D by users this could not be done.
For this reason upgrades will be circulated as new information and
techniques are made available.

The current level of developement would not have been possible had it
not been for invaluable help and advice from the following; Tim Strachan,
Knud Pedersen, Graham and Stuart Boyd, Jon Benjamin, Tom Whiteley, Richard
Wynn, Peter Mills and the Technical staff at Channel 9 in Sydney.

HARDWARE

When you purchased Digiview a plastic four colour frisby was provided to
entertain the kids while you were busy at the computer. Unfortunately it is
not particularly durable and will quickly break. I suggest that the makers
consider using a softer plastic material!  Or perhaps discontinue the idea
altogether!

Before you consider digitizing seriously your first additional purchase
should be for the following camera filters. They are obtainable from any
well stocked photographic store. Expect to pay about $30 each.  For ease of
use 55mm or larger should be ultilized. Size is important as you may find
it easier to hand-hold the filters rather than to custom build a suitable
frame. The filters must be glass. For quality results, DO NOT USE PLASTIC
ALTERNATIVES!

                   Red R (25a)
                   Green G (X1)
                   Blue 80b (You will need two screwed together)

Matched sets of three filters (RGB POP) are available if you are prepared
to wait while they are ordered in. The set will cost about $60, about half
the cost of buying them individually as indicated above.
Quality glass filters will eliminate most of the "fringing" (red or green
bleed where light and dark meet) and will improve the image resolution.

If you use an unmatched set of filters you may find it necessary to
increase the green value with the slider in the colour adjustment section
of the software to improve pictures containing yellow. The green filter
recommended is commonly available, but it needs to be slightly darker.

When light passes through an object it defracts, different components of
the colour will take a different route.  For example red will reach it's
destination in a different position to blue. Consequently the picture will
not be sharp and will contain information not present in the original. To
varying degrees the lens you are using with the camera was designed to
cancel out this phenomenon by incorporating additional elements. As a rule
of thumb, the more elements the better final result. The integrity of the
lens will be degraded if a substandard medium is placed in front of it.

DIGI-VIEW INTERFACE

This unit will plug directly into the parallel port of the A1000, but will
require a "Gender Bender" to operate on later machines.

LIGHTING

This is the second most important area that must be considered and probably
the most difficult. Although good results may be obtained with other globes
the best results to date have been obtained using two 500W colour corrected
Photo Copying globes. These are readily available from well stocked
photographic dealers. They will set you back about $30 each. You will also
require two screw type globe mounts which are available at Dick Smith and
in the electrical section of SOME large hardware stores. Lower output
globes such as 250W may do the job but you will find that you will be
restricted. In a typical situation 500W globes will give you enough light.
Generally the F stop setting would be somewhere between the range of f4 -
f8, giving plenty of latitude either side of this setting.

LIGHTING SETUP

Although each setup is different, use these recommendations as a guide to
get you started. The camera should be central between the two globes. That
is, the globes and the camera should form a straight line. The globes MUST
be behind the face of the lens and should be directed at the subject at an
angle of 45 degrees. The globes should be positioned about 1.3 metres
apart. Wider settings can be used, requiring a wider opening of the iris
(aperture) in the lens of the camera.

CAMERA

The people from Newtek recommend the National WV-1410N/A security camera.
This is an excellent camera. However for digitizing it suffers a serious
drawback, it does not support manual override of the Auto Light
Compensation. It is not possible to modify the camera  to disable this
function because the circuitry involved is contained in a chip. Good pics
can be produced with this unit but they will appear flat, lacking
brightness and contrast. Grain will also be more evident because insuff-
icient lighting levels will be passed on to the computer. Whats more,
good results can take longer to produce when compared to the recommended
camera below.  The National camera provides 550 lines of resolution
measured at the centre, which is quite good for most purposes.  A ready
made camera for digitizing is the Hitachi HV720K which has superior
resolution (600 lines) and an internal switch to disable the ALC
mentioned above. With the correct set-up and experience this camera will
produce results comparable to those produced with a  broadcast camera.
They are distributed by AWA and as an added bonus are cheaper than the
National unit mentioned.

Quite good results can be obtained with a colour video camera, but not in
its standard form. Without modification, pictures will contain strong
diagonal lines closely set together. These are caused by the Colour Sub
Carrier. This can easily be removed prior to digitizing with a 75ohm
Rejection Filter notched at 4.43 Mhz. This should be fitted between the
camera and the computer. BNC connectors are provided on the unit. Tube
type (as opposed to CCD) colour video cameras generally produce a
resolution less than the B&W cameras already mentioned. Check your camera
manual. If a colour camera is used vertical mounting will probably be
impractical due to the narrow field of view of the lens, requiring the
source object to be placed at a greater distance from the camera than
would normally be the case.

SECOND MONITOR

If you have a VCR that allows video in/out and a B&W (or colour)
television on hand you will be able to use the television as a focusing
monitor. Connect the camera output to the VCR video input, VCR video
output to the computer via the digiview interface. Connect the VCR RF
output to the television. You will need to tune the television to receive
the VCR RF signal.

MEMORY

To use all the modes of Digiview (PAL version) you will require 1.5 Meg
of RAM. However, 1 Meg will provide you with all modes except Hi-Res
colour. The programme will not load on a 512k machine.  Up to and
including version 3.0 release of the software only 16 colours are
supported in Hi-Res. This mode is not particularly useful for general
work. With Version 2.0 the best quality results will be produced using
Interlace. A preliminary appraisal of Version 3.0 seems to indicate an
improvement in image quality (over Version 2.0) when using Lo-Res.

CAMERA CARE

Video cameras give the best results in bright light, yet this can be
harmful to the tube, particularly its light sensitive surface. A camera
with a manual iris is particularly vulnerable (the Hatachi HV720K has
manual override). Tube burns are caused by bright light producing a dark
spot on the surface of the tube. Depending on the severity of the burn,
it may be removed by turning the camera on and aiming it at a brightly
lit white surface for an hour or so. If this has no effect, try leaving
the camera operating for a day or two with the lens cap in place.

Some spots on the image may be caused by specks of dirt on the lens, or
even on the target surface of the camera tube. Use a lens cleaning tissue
when cleaning these surfaces. Do not apply pressure as this can remove
the lens coating. Take particular care if cleaning the face of the tube
as undue pressure will disturb the tube alignment. New and old camera
tubes should be inspected.

SCREEN WIDTH

Use a sheet of stiff (for durability) white cardboard. Draw different
sized circles or squares on the card. This will allow  settings to be
made at different camera distances. Make a single pass and measure the
height and width. Adjust the WIDTH in the CAMERA window until both
measurements are the same. Each mode (resolution) will require different
settings.

LIGHT BALANCE

As the above mentioned card is white it can also be used to test the
lighting balance. For speed in setting-up, use the Lo-Res 5 second scan.
Make a single pass and adjust the lights until an even shade on the image
is obtained. To get good results you will need to spend some time in this
area.

JITTER

Not to be confused with flicker, jitter is a vertical section of the
image up to about 5cms wide that moves rapidly up and down. This is not
a problem in Lo-Res. However, in other modes it can be a major disaster.
Reducing image sharpness will help but will not eliminate it. The high
light levels required with digitizing also accentuate the vertical
movement. In the CAMERA window there is a TRACK slider. Like most users
you were probably unable to see any modification to the image when you
moved this. It's function is to move the offending section of the image
out of the screen area.

Make a single pass with the red filter in place. If there is any
vertical movement in the image, move the TRACK slider one click in
either direction. Keep repeating this until a stable image is obtained.
Don't dispair, sometimes it can take quite a while. When the red
component of the image is correct, try the green (while retaining the
red image on screen as normal). If that is unstable you will need to go
back to red to make some minor adjustments. If there is any movement
when you get to the blue component, display the picture. In most cases
it will be stable.

UNEVEN COLOUR

Sometimes it is possible to produce an image with a darker vertical
section on the left hand side about 2cms wide. This is caused by placing
a filter in front of the lens just before digitizing. The camera requires
a few seconds to adjust to the different lighting. Allow about 5 seconds.

FILTER LOCATION

The filters should be located as close as possible to the lens. This will
help improve the image and will also reduce lens flare caused by light
reflecting off the top of the filter. Don't overlook room lighting if you
experience problems in this area.

CONTRIBUTIONS

If you feel that you have tips that can help other users,  write to the
author via Tim at MEGADISC. As mentioned previously, this article will
be upgraded as new information becomes available. If enough interest is
indicated (through your letters) other services could be made available.
Consideration is being given to compiling a dedicated disk that would
include example pics (including faults) ranging from a basic setup to
those produced on a $200,000 camera. Let us know what you want, share
your work, but most importantly, share your tips!

XXXXXXXXXXXXXXXXXXXXXXXXX END OF ABOUT_DIGITISING XXXXXXXXXXXXXXXXXXXXXXX