Scanning Ancient Coins
The discussion that follows is not an expert discussion of coin imaging. It is simply an explanation of the techniques used to produce some of the coin images on this site. Some of these images show degradation from being saved as compressed .jpg's. Over the time that I have maintained this site I have moved to slightly higher levels of compression to make my pages load more quickly. While I am rarely bothered by this 'noise', it does show on some of these images and should not be seen as an error of the scanner.
|This image of a Septimius Severus Greek Imperial bronze was one of the first I produced directly from the coin using a low priced flat bed scanner. After scanning the image was rotated to correct the orientation. Contrast and density were adjusted in software. Separate images of the two sides were combined in software and a paint fill tool was used to make the background an even black.|
Until recently I believed that the first requirement for taking coin pictures to be a decent camera but in the last year I have been playing with scanning images directly from the coins using a flat bed scanner. I have to admit that I am impressed with the results and, considering that the scanner is almost instant and cheaper than most suitable cameras, many of you would be well advised to take this route to coin photography. The brand of scanner is not important. My current unit is a 600x1200 dpi rated Plustek but dozens of other brands will do as well or (?) better. The feature that makes the direct scanner work is also its great shortcoming. A scan is made by passing a light down the page reflecting the image into the pickup that travels right along with the light. The angle between the light and the pickup is fixed so the only control available to the photographer is rotating the coin on the glass so the light will appear to be coming from a different direction.
Direction of the light is a factor that should not be obvious when looking at the photograph. If the average viewer notices that the light is coming from a certain direction it is likely that the result was unnatural. For most uses best results will be when the light appears to come from the top of the coin. On some scanners this means placing the coin upside down on the scanner glass and using the image manipulation software to rotate the scan so the top of the coin is up. My first scanner required this technique. My second unit, from the same manufacturer, does not. You will need to experiment to determine the best technique for your equipment. Never light a coin from the bottom. The effect is reminiscent of Halloween ghouls holding flashlights shining up on their faces.
Software (which usually comes with the scanner and can be quite complex) will allow adjustment of contrast, brightness and color balance. I recommend that beginners try the software that comes with their scanner before buying one of the top end programs (Photoshop, for example) and see if your particular needs are filled by the lesser software. There certainly is a place in this world for great programs like Photoshop but if you are not going to use all those features you might find that the packaged software will leave you less confused and with several hundred dollars that you can spend on coins. Really good software might cost as much as the scanner. There are excellent programs available for download on the web as shareware. Paint Shop Pro by JASC is particularly good.
Usually you are given two chances to adjust contrast and density of the scan. Before scanning, try to set the controls somewhere near what will give a decent image. After scanning use the available controls to fine tune the results and to balance the images of the two sides of the coin. The exact operation of these controls will differ according to the software used. The composite below shows three paired images scanned at different settings for brightness (first number) and contrast (second number). My scanner default is 50/50 which usually produces a decent image from a paper photograph. Obviously the correct setting is different for bright silver and dark bronze coins.
Before scanning you will have to tell the software the resolution you want to use. When working directly from the coin I generally use a rather high setting like 600 dpi on the theory that I can always downsize the file later to fit the use intended. There is no reason to scan at a resolution higher than the 'optical' rating of your scanner. Some units that produce larger files through software but actual detail is limited to the 'optical' rating. High end scanners are capable of extremely high resolutions that will produce a file larger than most of us have available in our computer's RAM. I bought 32 Meg (not enough to avoid using the hard drive for large images) with my old computer and 128 Meg on the new one (may be enough?). For many uses scanning at 150 to 300 dpi will produce acceptable results. Set the scanning software only to scan the area of the bed on which you have placed the coin. There is no reason to scan an 8 ½ X 11 inch area to record a 1 inch diameter coin! If your software offers a 'prescan' feature (most do) this cropping is quite simple.
|Scanner lid open||Scanner lid closed||White 'Shadow Box'|
|1 Remove||2 Straighten||3 Fine Tune||4 Color||5 Add Photo|
Whichever background is selected for scanning can be removed either by using a 'Paint' tool or by cutting around the edges of the image with a 'Magic Wand' that senses the changes in brightness and cuts along the edges. Image (1) above is the result of using the 'Magic Wand' on the 'Shadow Box' image. If the coin is not quite straight, it can be rotated (2). The image can be improved by applying a 'Sharpen' filter (3) or by fine tuning the brightness and contrast. The old background removed, a new color (4) can be added using a 'fill' tool or the image (5) can be dropped on a background image. I would stop at (3) but you can do whatever seems right.
A pet peeve of mine: Some people refuse to join the two images into one file and expect me to pull up two separate files to see both sides of the coin. I see absolutely no reason not to use the cut and paste tools provided to produce one file trimmed of all the extraneous background area even if you don't take the time to fine tune the image in every way possible using the software tools. Our subject is a small bronze (AE15) of the Seleukid ruler Demetrios I (162-150 BC). Far from the most beautiful coin on this site, its varied surfaces provided quite a challenge to produce even this good of an image. Still, the image at this point has not been retouched and is an accurate rendition of the coin. Selective retouching could produce a more pleasing image of the horsehead obverse if the result were not to be used for selling the coin (it is not for sale, by the way). The scanner would have done a better job on a larger coin or on one with a friendlier surface (like toned silver). Some coins seem to resist my imaging efforts (camera or scanner!) but others look so much better on the screen that I would have to attach a disclaimer if using the image for selling. If the purpose is to illustrate an article, software tricks allow 'improvements' that, skillfully used, could mask many flaws.
I feel foolish mentioning these points but, considering some of the images sent to me for identification, it is necessary. You MUST remove the coin from the holder before scanning. Even the thinnest plastic used on cardboard flips inserts a barrier that greatly reduces your chance of a good scan. If you don't want an image of the coin badly enough to remove it from the holder, you are wasting your time reading this page. The chance of your coin scratching the glass top of the scanner is very slight. Glass is harder than metal. If your scanner has a plastic 'glass' or if the coin has sand trapped in the patina, there is a chance that a scratch could occur. Care in placing the coin on the glass and not rubbing it around on the glass should remove the chances of a scratch. If you wish to be extra cautious, try scanning direct scans at the bottom of the page where the scanner is never used. My unit has enough room below the letter size mark to fit a denarius. If you are from a place that uses the longer A4 format paper, this will not work. Just be careful. Fingerprints on the glass usually are not a problem but cleaning the glass will hurt nothing. End of lecture.
Until advances in technology make professional digital cameras available at a lower price, most of us will continue to use conventional single lens reflex cameras for coin photography. A professional camera and accessories to make conventional coin images will cost as much as many digital cameras. Current (November 1998) prices makes direct scanning the only way to image coins for under $100. Decisions on exact equipment and materials are not as important as learning to use the equipment to its full potential. To accomplish this the photographer will do a lot of "trial and error" work until experience with a wide variety of coins can be gained.
While questions and samples of problems are welcomed, I ask that any attached images be no larger than 600x300 pixels and sent in .jpg format. Someone once sent me a large .bmp that took half an hour to download. Please don't do that. If you have web space, please post the photos and send the URL with your questions/comments.
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(c) 1997 Doug Smith