

This article appears on The Chuck D'Ambra Web Site
and are Chucks' own tips gathered through years of
scanning experience.  Chuck is very experienced at
scanning of Coinage.  I found his tips to be very
helpful.  The Web Site page is http://www.sni.n
et/ts/coins/scanning.html.

Tips for Scanning Coins by Chuck D'Ambra

This document discusses in detail many aspects of
creating scanned digital images of coins and
similar numismatic items.  Important technical
factors are explained for those who may need or
like to better understand the trade-offs and other
issues in volved in the process.  Next,
suggestions on equipment and software for scanning
coins are provided.  Finally, an easy to follow
procedure gives step by step instructions for
creating scanned coin images suitable for the Web.

        Background

        Technical Considerations

                Scanning Coins vs. Scanning Coin
                  Photographs
                Image Resolution
                Monitor Resolution
                Magnification, Storage and
                  Download Time Considerations
                Thumbnails
                Image Formats

Choosing Hardware and Software
                Chuck's Setup

Step by Step Procedure

Background

Scanned images of coins can be used for many
 purposes, not the least of which is to
 &quot;spruce up&quot; any numismatic Web site.  I
 began scanning coins and including the results on
 the Web more than 2 years ago. After numerous
 requests for tips on scanning coins, I created
 this page to make detailed information available
 to everyone.

This discussion is oriented towards producing coin
images for display on computer monitors, such as
on Web sites, but many points are applicable when
the intended result is hardcopy.

Technical Considerations

Since the goal is not just to create coin images
but to create high quality images that , let's
first look at some of the major technical factors
that come into play.

Scanning Coins vs. Scanning Coin Photographs

Perhaps the most frequently asked question on this
subject is whether it's better to scan coins
directly or to photograph them and scan prints of
the film.

The answer depends on your objective.  Film offers
much higher resolution than scanners currently
available in the local computer store. Should you
need to get high magnification images of coin
details, for example, of die doubling and
repunched mint marks, photographing the coins at
high magnification and subsequently scanning
prints of the film will produce superior results.
This two step approach may also produce better
results for very high relief or dark coins.

For general purpose images at low to medium
magnification, placing the coin itself on a
flatbed scanner is faster, less expensive and, in
my opinion, often produces better results than
scanning a photograph.  You can easily get quality
images of up t o 70 times actual size (see next
two sections) with scanners currently priced at
under US $1000.

All coin images on Chuck Coins web site were
produced by scanning coins directly on a flatbed
scanner.

Image Resolution

When an object is scanned, a digital
representation is created. A matrix of discrete
"picture elements"  (pixels) representing
individual points on the surface form a picture of
the original object.

The image resolution or scanning resolution is the
number of samples per unit of distance. The higher
the scanning resolution, the finer the details
that will be present in the resulting image. Of
course, as resolution increases, more disk space
and other resources are required to store and use
the image, too.

The optimum resolutions to scan and display coins
depend on factors considered below. In most cases,
the image resolution will be between 72 and 600
pixels per inch (also known as "dots per inch -
divide dpi by 2.54 to get dots per centimeter).

Because an image has two dimensions - a width and
a height - s size (number of pixels) increases
proportionally to the square of the scanning
resolution.  When you double the scanning
resolution, say from 150 to 300 dpi, the result is
four times as m any pixels.

Monitor Resolution

Computer monitors display many thousands of
pixels.  The monitor resolution or, more
generally, device resolution is a measure of how
closely spaced the pixels are displayed. Monitor
resolutions vary from one computer to another and
are even configur able on some machines.  In many
cases, monitor resolution is at or near 72 dpi.

Because monitor resolution varies from one
computer to another, the physical size of a given
image also varies between the machines. An image
that is 72 pixels wide and 72 pixels high will be
displayed in a one inch by one inch square when
the monito r resolution is 72 dpi.  On another
computer with a monitor resolution of 100 dpi, the
same image will appear smaller, because the pixels
are spaced closer together.

The very important point here is that the width
and height of an image may be substantially
different when viewed on a different computer or
when printed. Some image processing programs
report size in units such as inches or
centimeters. In my opinio n, that confuses the
issue, because it's based on an assumption about
device resolution which is invalid when images are
shared over computer networks. It's more useful to
know the width and height of an image in pixels,
since they are device indepen dent. To determine
the physical size for any specific device, divide
the number of pixels by the device resolution.

Magnification, Storage and Download Time
Considerations

Scanning at higher resolution captures finer
details in a coin. On the other hand, the
resulting image occupies more disk space and takes
more time to transfer over a computer network,
such as when downloaded from a Web site.

The longer it takes to download something on the
Net, the greater the chance that the viewer will
decide to interrupt the transfer and go to another
site. My rule of thumb is that a web page should
download over a 28.8K modem in under 30 seconds
(som e connections are slower and therefore
download time is longer). That means the total
size of all files used in the page should be
limited to about 100 kilobytes.

Ideally, magnification is high enough for the
design details of the coin to be clear and small
enough that the file size is not too large.

Thumbnails

A single high resolution coin image can be a few
hundred kilobytes to over a megabyte. A useful
technique for making large images available is to
include a much smaller "thumbnai" version of the
image in a document and link it to the high
resolution image. Download time for the main
document does not become excessive, and anyone
interested can see the enlarged version by
clicking on the thumbnail. The gold coin  pictured
here is an example.

Image Formats

After scanning a coin,  you will save the image in
a file.  There are literally dozens of digital
image file formats and a lot of software for
converting from one format to another. Images used
on the Web should be in a format that browsers
will disp lay. The only two formats which
virtually all Web browsers are currently capable
of displaying are:

Compuserve Graphics Interchange Format

Photographics Experiment Group (JPEG) format

GIF generally gives better results for digitally
created art work, and JPEG generally gives better
results for photographs. Either format is suitable
for most coin scans. JPEG images can frequently be
stored in somewhat less
disk space. GIF has the advantage that an image
can have a transparent background. One color can
be designated as transparent - in our case, the
color outside the perimeter of the coin would be
selected. Whatever lies underneath transparent
portions of the image (e.g. the background of a
web page) will be displayed by software that
supports transparency, including most browsers.
For me, transparency tilts the balance in favor of
GIF for most coin images on the Web.

Choosing Hardware and Software

If you don't already have a scanner, you may be
wondering which ones are suitable for scanning
coins (and anything else you expect to scan).
You'll also need software to drive the scanner and
to manipulate and save the images you create.

Handheld scanners are not suitable for scanning
coins.  A flatbed scanner is mandatory. You will
need a model with a communications interface
compatible with your computer. PC and Mac versions
of many popular models are available.

Many scanners come with software which attempts to
produce higher resolutions images than the device
can actually "see"  by interpolating between
pixels. This "enhanced" resolution is often cited
in advertising for the product.  Ignore it!  The
only figure that matters is the optical resolution
of the scanner.  No additional details are
captured at resolutions higher than the optical
resolution.

For professional use, I recommend a scanner with
an optical resolution of at least 600 dpi.  At 600
dpi, details of die varieties with significant
"spread"can be captured. A number of flatbed
scanners with 600 dpi optical resolution are
available for under US$1000.  For occasional,
personal use, 300 dpi may be satisfactory.  Images
on the Web will usually be at a lower resolution
anyway.  Flatbed scanners with 300 dpi optical
resolution are available for under US$400.

Scanners are often bundled with an image
processing program, and other software can be
purchased separately.  Among the most popular
packages are Corel PhotoPaint and Adobe Photoshop.
Keep in mind that you will probably want to use
the software for a lot more than just driving the
scanner (e.g. to annotate images or to create
special effects). In my opinion, Photoshop is the
best image processing program available for PC
class computers.

Chuck's Setup

All the coin images currently included on Chuck
D'Ambra Coins Web Site were scanned on an HP
Scanjet 4C and subsequently manipulated as
described below with Adobe Photoshop on a Power
Macintosh.  I am completely satisfied with this
setup, but other c hoices may also provide
satisfactory results.

The procedure below includes instructions specific
to my setup. Details will differ somewhat for
other hardware and software.

Step by Step Procedure

Once your scanner and image processing software
are installed, we're ready to scan! The process
may appear to be long and complicated. That's only
because I've described it in great detail, so that
most anyone will be able to follow along. After
litt le practice, you should be able to scan,
process and save an image of one side of coin in
less than 10 minutes.

Some of the instructions below are specific to my
setup, but the process will be similar with
others. Check the manuals for your scanner and
software when you don't find options in the places
indicated below.

Note: steps 16 and 17 were applied to the
intermediate images included at steps, 11 and 12,
so that they would be visible in Web document.

1. Getting Started. Turn on the scanner and start
up your image processing program. Place one or
more coins on the scanner surface. A soft flip, or
something similar, will help protect the coin from
damage when the lid is closed. The Scanjet 4C
makes it appear that light source is located at
its front. Rotate the coin so that the light hits
the devices from complementary direction.  Avoid
dragging coins or other objects on the scanner
surface!

2. Preview. Direct the image processing program to
import an image from the scanner (in Photoshop
4.0, File->Import->Twain Acquire). The software
may launch another program that drives the scanner
(for my Scanjet 4C, the DeskScan II program that
came with it). Start a "Preview" operation, if it
isn't launched automatically. A preview is low
quality image of what's on the scanner surface.

3.  Image Type.  Scanner drivers often have
multiple image types, such as black and white
drawing and color photo, and may guess which one
best applies to what's on the scanner. Millions of
Colors works best for coins. If necessary,
override the "Typ e" accordingly.

4. Set the Scanner Resolution.  You can and will
tweak the image after the actual scan. First, you
must get the raw working material. The most
important parameter to set at this point is the
resolution of the image you will import. In
general, the be st results are obtained by
scanning at higher resolution than will be
ultimately displayed (reducing the resolution is
discussed below). I often scan coins at 300 dpi
resolution.  Higher resolutions are advisable for
RPMs, die doubling and other fine details,
although going above the optical resolution of the
scanner buys you little if any improvement in
detail.

The interface to set the scanner resolution is
effectively hidden by the DeskScan II interface.
Click "Custom" and select "Print Path" from the
pulldown menu. Enter the desired scanning
resolutions in the Horizontal and Vertical
Resolution boxes. Giv e the configuration a name,
then click on the "Add" button followed by the
"OK" button. You'll only need to do this once for
each scan resolution. Later, you will be able to
choose settings from the Path
pulldown menu.

Change the "Path" setting to get the desired
scanning resolution, if necessary.

5. Zoom on the Area of Interest. Click on the
preview image outside the rectangular selection
area created during the preview to remove
the rectangle. Drag a new rectangle encompassing
the actual area of interest  (the rectangle need
not be right at the borders of the coin, as
excessive space will be cropped later). Click
"Zoom" in the software window to get a close up of
the area se lected.

6. Adjust Brightness and Contrast.  Re-select the
area of interest again, if necessary. Note the
Brightness and Contrast settings, in case you want
to return to them. Click the button and the
Brightness and Contrast will be automatically
adjusted for the selection area. Manually change
the values, if not satisfied with the automatic
levels.  You'll be able to fine tune these
parameters later, but any unusually dark areas
should be removed now by increasing the brightness
and/or reducing the cont rast.

7. Import the Image. Click the "Final button" (or
equivalent) to scan the image into your image
processing program.

8. Save the Raw Image. Save a copy of the image in
the software's native format before doing much to
it. If you later decide to do things differently,
you can open the saved image rather than scanning
the coin again.

9. Cropping and Rotating.  Crop excessive space
around the coin. Rotate the image to the desired
orientation, as necessary. In Photoshop 4.0,
select "Rotate Canvas" from the Image pulldown
menu. An "Arbitrary" rotation angle is usually
necessary. In fact, you will probably need to
rotate, undo the operation, and redo it a few
times to get the right angle. Save the image again
(this is the last time overwriting the originally
saved copy is advisable).

Grey parts of the background in the adjacent image
are from the original scan. White parts are the
result of new pixels added to the image during
rotation.

10.  Color and Brightness.  Adjust the color and
brightness settings, if desired (I usually don't).

11.  Image Resolution. The remaining steps involve
preparing your image for where it will be
displayed, which is assumed here to be on the Web.
Reduce the image resolution to the final value. I
use 150 dpi for most coins or 300 dpi for smaller
coins which may require it for all legends to be
clear. In Photoshop 4.0, select "Image Size" from
the Image pulldown menu, change the Resolution to
the desired value and click on the "OK" button.

12. Sharpen the Image. Details in the reduced size
image can be made clearer by performing a Sharpen
operation. For Photoshop 4.0, select "Sharpen"
from the "Filters" pulldown menu.  The regular
Sharpen option in the submenu that appears seems
to wor k best most of the time.

At this point we could jump to step 16 and save a
usable image. If you want to include both sides in
one file, continue with step 13.

13.  Scan the Other Side. Repeat steps 2-12 for
the other side of the coin.

14.  Open a New Window.  Create a new frame (File-
New) large enough for both sides of the coin.
Make sure the color mode is RGB, not indexed.
Choose a background color that's not in the coin
images (white usually works).

15.  Copy the Image to the New Window.  Next, we
want to copy each side of the coin, minus the
noise outside it to the new window. It make take
some work for a coin that's not disk shaped. If it
is, crop virtually all excess space on the left
and top sides of the coin (makes the next part a
lot easier). Drag an elliptical marquee around the
coin. The goal is to exclude everything outside
the coin without losing any of the coin itself.
Copy the selected area to your computer's
clipboard (Edit->Co py). Drag the marquee into the
new frame. Move it to one side of the frame or the
other. Copy the contents of the clipboard into the
new window (Edit->Paste).  Repeat with the image
of the other side of the coin.

16.  Convert to Indexed Color.  When the final
format is JPEG or another RGB format, proceed to
step 17. For GIF images, the image type must be
converted from RGB to Indexed Color. Because no
more than 256 colors can be displayed
simultaneously in mo st web browsers - and that's
for everything in it, not just one image - use no
more than 128 (7 bit) color. In most cases 32 or
64 colors (5 or 6 bits) are enough.  If you're
prompted about flattening the image, do it.

17.  Save the Image.  Select Save As from the File
pulldown menu. Set the output format to JPEG or
GIF, as desired, enter a new filename, and click
OK.

18.  Make the Image Background Transparent
(optional). I use a separate software tool for
this purpose.

Congratulations, you now have a high quality
digital coin image!
