Scanner on the market change as fast as most other computer peripherals. Most will be on sale for at most 6 months. Luckily prices are dropping and never models are more powerful and cheaper. First advice in this kind of market is not to buy until you actually have the free time to use it.
I purchased a 300 dpi Paperport 3100 scanner for $105 a few years ago which worked on the parallel port shared with the Printer. I replaced it in 2000 with a 600 dpi ACER 640U scanner for $65 which work on the USB port which is faster. In 2002 I perchased a Artec e+48U 600 dpi scanner for $25 after a $60 mail in rebate.
Since it is now low cost it is best to get at least 600 dpi. However it is also important to test how long it takes to do a preview. My scanner takes under 6 seconds which is good. There are some old slow refurbished models on the market. I tried one out with an IBM brand name which took over a minute and was so slow that I was glad to be able to return it even at a loss of 15% restocking fee.
Image size is an important consideration for putting coins on the web. I find images smaller than about 200 pixels on each side too small and larger than about 500 pixels too large. A US penny diameter 19 mm scanned at 300 dpi is 225 pixels. In general for this website coins smaller than a US penny is therefore scanned at 600 dpi and larger coins at 300 dpi. I sometimes use 600 dpi for more valuable coins which are slightly larger (under 21 mm). At 600 dpi even Fanams are about 200 pixels. If the scanned image is too large for screen it can be displayed on the page at reduced resolution using the width= or height= tags within the HTML <img src="imagefile.jpg"> image display command on Netscape like web browser. The reader can look at the image in full resolution by opening the image with "view image" or some such browser task which does not need to be reloaded since it is already in the cache full available resolution. Note it is best to use only one of the tags height= or width= to avoid accidentally distorting the image by non-identical scaling. To have the coin printout at the actual size I find I need to display at 100 dpi but I have not confirmed if that is independent of browser used and printer
Occationally resoluting higher than 600 dpi is needed to highlight a small region of a coin like a MintMark. In case like this I use images from a toy QX3 USB Microscope I purchased for just $40 including shipping.
The direction with which the coin is illuminated by the scanner is also important for high releaf coins since shadows could significantly change the appearance of the image. Except for Proof condition coins scans higher than 600 dpi start showing imperfections on the metal surface on most coins and doesn't make a nice image. Silver Proof coins look black because of the high reflectivity and should probably be photographed with a digital camera. See comparison I have not as yet experimented with them. They do look sort of ok when displayed in reverse video, and almost like what they look like. Need to then Scan with a Black background which will reverse to white.
For simplicity of handling it is best to crop images initialy leaving only about 10% border around coin which is useful when rotating the scanned image to be perfectly upright. Any basic scanner software can do this. I am amazed at how many images of coins are are posted on ebay at 30dpi since the seller doesn't want to learn how to crop and scan only the coin. When I ask them for a larger 300dpi scan they send me 2450x3300 pixel image which is mostly Black or White with sometimes a 100 pixel diameter image of small coin lost in it. This has happend too often and I am almost scared to ask :-)
It is worth color editing the images of darker coins to highlight detail. See details of using PhotoShop. Most basic software provided with scanners have provision to do this. You need software which can rotate an image to at least a resolution of one degree, which can be easily noticed but practically impossible accuracy to align on scanner surface. If processing a large number it maybe quicker to print out an array using a temporary HTML page hand draw the vertical and measure the required angle with protracter. I use XV which has lots of nice features. It appears to have a better image compression than my scanner software. The mean image size of about 300 coins scanned so far is 17 Kbytes with a mode at 10 Kbytes and should load in few seconds even on dial-in 56 Kbits per second dial-in Modem. About 90% of the images are under 33 Kbytes with the largest image size being 70 Kbytes.
Image formats and compression, is an important issue. JPG files are lot smaller than GIF files of the same dimension. GIF files are better for special effects such as animated-gifs I find more annoying than useful as a highlight. The content of a page and the resolution of the graphics should be in the forefront when selecting between various options to reduce download times.
BMP files are large and uncompressed. Each pixel is represented by 8-bit (256 colors) or 24-bit (16-million colors) when a small 100x100 pixel image is 30KB. It is microsoft based and has limited support on other computer systems. Other MicroSoft Formats such as .TIF .PPS etc should also be avoided. I have noticed .PPS (Powerpoint) to compress the X and Y of the images differently I just don't understand why Microsoft is so ignorant of basics of default image handling. For most web images 8 bits is enough. .GIF is an 8-bit compressed image format which is also loss-less, or the original can be recovered exactly. It is useful for line drawing with a lot of white or single color background. With both .BMP and .GIF color transformations if known can be reversed to recover original exactly. However .JPG is a lossy compression in which you compromise quality to reduce file size. As the quality is reduced the image gradually becomes less sharp. Multiple transformations of jpg images decay the image quality. Because of the .JPG image compression saving as 8-bit or 24-bit changes the resulting file size only slightly. I save scanned images initially at 90% quality jpg and then after rotation and then cropping save at 50-75% JPG quality. The required rotation which is easy to estimate by trial and error to about one degree accuracy. Note that multiple rotations also decay an image, so the original is transfomed by one single rotation.
A lower JPG quality may make images smaller. A JPG quality less than 40% shows noticeable degradation of the image with no significant reduction in image size. Probably after some serious study the over 100 years of National Geographic issues released on 30 CDROMS was scanned at 100 dpi and saved as 40% JPG quality.
Coins are best scanned kept directly on the glass surface. I don't generally buy slabed coins, popular in US, but very rare coins. The cost of Slabing is not worth in any case for most coins, and the rare dumps are often more than the 3.8 mm maximum thickness, and the Bar more than the 40.6 mm maximum diameter; as specified for example by ANACS which otherwise grades any coin listed in the Krause Catalog. PCGS only grades any machine struck coin made since 1700.
Images like that of coins printed in most books and magazines are composed of dots. Scanning
at a resolution higher or close to the number of dots per inch on the images
can lead to interference patterns which some scanner software correct using
an option called DESCREEN. To select the scanning resolution it is
necessary to first determine the dot per inch on the printed page. Some
scanner software has an auto-detection which I however found to be unreliable.
I find it very easy to determine it by counting the number of dots I see across
the 1.1 mm field of view of my RadioShack 100X magnifier.
For example I count
| 1.1 mm | Inch | Type | Examples - (AC=>Auction Catalog) |
| 4 Dots | 85 | newsprint | |
| 5 Dots | 100 | Books | Delmonte,Krause |
| 6 Dots | 133 | Magazine | GroganAC,TMDeSA,Pridmore,Codrington'1975 |
| 7 Dots | 150 | Scholten,PridmoreAC,Sallay,Seyone,Ruhuna,WigginsAC | |
| 8 Dots | 173 | Art Magazine | Marsh |
| 14 Dots | 300 | ComputerScans | |
| Engraved | Codrington'1924 |
The highest quality is when you get images with No dots which are engravings for example like used on Currency Notes and some stamps. The Text in books are also made up of Engraved fonts and therefore it is useful to use the highest practical resolution for Optical Character Recognision (OCR).
It is important to recognize that a scanned image posted on the web does not give any information about the physical characteristics of the coin. Indications such as "200% of real size" or whatever I often see is not a useful measure since all of us don't use the same size of computer screen. If the dpi (dots per inch) of scanning is given then from the size of the image the diameter can be worked out. However it is best to measure Physical characteristics the diameter/thickness to 0.1 mm and if available the weight to 0.01 grams.
