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Written by Chuck D'Ambra
This document discusses in detail many aspects of creating digital images of coins and similar numismatic items with a scanner. Important technical factors are explained for those who may need or like to better understand the trade-offs and other issues involved 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 world wide web.
NOTE: The original version of this document was written in early 1997. Digital cameras have advanced considerably since then. If you're deciding between purchasing a scanner or a digital camera, the camera may now be the better alternative, especially since it can be used for other things that a scanner cannot. Image "post-processing" - described in the Step by Step Procedure below - is similar.
Background
Choosing Hardware and Software
Scanned images of coins can be used for many purposes, not the least of which is to "spruce up" any numismatic web site. I began scanning coins and including the results on the web in 1994. 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 to be displayed on computer monitors, such as on web sites. Many points are also applicable when the intended result is hardcopy.
Since the goal is not just to create coin images but high quality images that enhance a web site, let's first look at some of the major technical factors that come into play.
Is it better to scan a coin directly or to photograph it and scan a print?
Placing the coin itself on a flatbed scanner is considerably faster and less expensive than shooting, printing and scanning a photograph. Scanning coins directly usually works well even with slabs (for best results, remove coins from flips and 2x2s). Scanning a photographic print may produce better results for high relief or dark coins.
A digital camera with a macro capability may provide comparable or superior results to a scanner. Scanners are great for capturing details but tend to produce "flat" images. Cameras are better suited for capturing the luster of uncirculated coins. Prior to 2001, all coin images on the Telesphere Numismatics web site were produced by scanning coins directly on a flatbed scanner. We have subsequently used digital cameras for all coin and paper money photographs.
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. Increasing the scanning resolution enables finer details to be captured. In most cases, it will be at least 72 pixels per inch (also known as "dots per inch" or "dpi"; divide dpi by 2.54 to get dots per centimeter).
Of course, as resolution increases, the size of the scanned image increases, too. Because an image has two dimensions - a width and a height - its size (number of pixels) increases proportionally to the square of the scanning resolution. Doubling the scanning resolution, say from 300 to 600 dpi, produces four times as many pixels. Assuming storage space is not an issue (it rarely is these days), scanning at a high resolution is recommended. However, you may need to resize your scans (reduce the number of pixels) for display online.
Computer monitors often display over 1 million pixels. The monitor resolution (or, more generally, device resolution) is a measure of how closely the pixels are displayed. Monitor resolutions vary from one computer to another and are even configurable 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 monitor 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 opinion, 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 independent. To determine the physical size for any specific device, divide the number of pixels by the device resolution.
When this article was originally written, the advantages of scanning at higher resolution had to be weighed against the disadvantages of using more disk space and slower downloads. Since abundant storage is now inexpensive and broadband networks are widespread, storage space and download time are usually no longer significant issues.
Even though we're no longer overly concerned about image storage space and download speed, we generally don't want web pages with enormous coin pictures. A combination of text and smaller pictures is usually more appealing. Still, there are times when a high resolution scan is useful, e.g. to show a die variety. A sometimes useful technique is to include a small "thumbnail" picture on the web page that is replaced by a higher resolution image when a specified event happens. The gold coin pictured here is an example. Move your mouse over the image to see a higher resolution picture of the same coin, then move it away from the large image to restore the thumbnail (if your browser doesn't support javascript or javascript has been disabled, click the thumbnail to see the higher resolution version).
After scanning a coin, you save the image in a file. There are numerous digital image file formats and a lot of software for converting from one format to another. Images used online should be in a format that major web browsers display:
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. GIF has the advantage that an image can have a transparent background. Because the color outside the perimeter of the small gold coin image in the "Thumbnails" section above has been made transparent, the background of the page goes right to the edge of coin. However, when the larger picture of the gold coin is displayed, there's a white background around it - it doesn't have a transparent background.
In my opinion, transparency tilts the balance in favor of GIF for coin images embedded in a mixed media web page, while higher quality makes JPEG preferable for photographs displayed on their own (e.g. in a separate popup or tab opened when a user clicks a link).
If you don't already have a scanner, you may be wondering which ones are suitable for 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. A scanner that uses a Charge-Coupled Device (CCD) sensor is preferable to one that uses a Contact Image Sensor (CIS). CCD scanners are better able to capture objects that are not directly on the scanner surface, such as coins in slabs.
Be sure to select a scanner compatible with your computer and its operating system and that uses a compatible communications interface. Some models work with both PCs and Macs. USB interfaces are common.
Some 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. For personal use, 300 dpi may be satisfactory. Flatbed scanners with adequate optical resolution are available for under US$100.
Scanners are sometimes bundled with image editing software. If satisfactory capabilities are not included with your scanner, software can be purchased separately. Among the most popular packages are those made by Corel and Adobe. Keep in mind that you'll probably want to use the software for more than just driving the scanner (e.g. to annotate images or to create special effects). Adobe Photoshop is a popular all around image processing program. A less expensive "light" version called Photoshop Elements may suffice for editing scanned coin images as well as most photographs.
All the coin images included on the Telesphere Numismatics web site prior to 2001 were scanned on an HP Scanjet 4C and subsequently manipulated as described below with Adobe Photoshop on an Apple computer (the Scanjet 4C was purchased in 1995 and has since been discontinued).
The procedure below includes instructions specific to this setup. Details will differ somewhat for other hardware and software.
Once your scanner and image processing software have been 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. With a little practice, you should be able to scan, process and save a "web-ready" image of one side of a coin in 5 to 10 minutes.
Some of the instructions below are specific to my setup, but the process will be similar with others. Check the documentation 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 shown at earlier steps, to make them visible in a web page.
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 usually 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 at the corners are the result
of new pixels added to the image during rotation.
Image Resolution.
The remaining steps involve preparing your image for display, which is assumed
here to be on the web. Reduce the image resolution to the final value, if not
the same as the scanned resolution. For inclusion on a web page, 150 dpi is
appropriate, except for smaller coins which may require 300 dpi for 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.
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 work best most of the time.
Congratulations, you now have a high quality digital coin image!