Features on ancient coins are not always easy to identify if some parts of the design are not clearly visible. The toning or residual corrosion on the coin can make it difficult to get a clear scan or photograph of it. To avoid any damage to coin one should not over clean it. Many of the details are however visible under magnification and in such cases, it is useful to make a line drawing. If there is text that is only partly visible (corroded or outside the flan), it may be possible to guess and draw the rest of the letter particularly if characters are known from other specimens.
Many numismatic publications include line drawings that are usually clearer than the photographs. Coins from Southern India by Sir Walter Elliot, published in 1886, illustrated the differences between prints from copper plates engraved by Indian artists. These plates make visible the minute detail of the coins. Even in the reprint of this book, the engraved first plate is very clear in comparison with the auto-type plates. Some of the low-cost publications from south-asia have used pencil rubbing but they are rarely useful and lot worse than good well-printed photographs.
Computer technology has now made line drawing easy for even non-artists like me. This web page contains my notes on how to create line drawings of coins. I hope you will find it useful to avoid some of the mistakes I made in my learning experience. I hope it encourages you to draw some of your ancient coins.
Image processing software like Photoshop has various tools that can be operated using a mouse. However, a mouse gives poor control compared to the drawing with the human hand. For example try signing your name with the mouse, a task we now often do in shops on a computer screen using a pen-like for credit card authorization. In reply to a question on Internet discussion group Moneta-L, Grzegorz Kryszczuk told me about WACOM products. They seem to be the trademark of choice for computer aided drawing instrument. There are many models over a wide price range. They include the older Graphire products, the more expensive Intuos products. For a few $K, the Cintiq tablet PC allows artists to work directly on a LCD touch screen. The USB Graphire2 and the newer Graphire3 models are reasonable entry-level devices and are probably as good for those without the artistic expertise to make optimum use of the more expensive and sophisticated devices.
I was able to purchase a Graphire3 4x5 (MSRP US$100) for $63.50 after
rebates (included a 2-year warranty and Sales Tax) from Circuit
City. It sells for around $90 on eBay. The 8.3 x 8.2 inch tablet
is plugged into a USB port and has a 3.6 x 5.0 active area. The light
cord-less, battery-less pen operates like the mouse on this
tablet. Although it works with Photoshop 7.0, it has clearly been
optimized for Adobe Photoshop Elements.
Also included is a cord and ball-less mouse that works on tablet if you want to get rid of a standard roller ball mouse. The tablet is attached by cord to USB, rather than the mouse to computer
Unlike the relative motion of a mouse, the pen on tablet uses absolute motion. Each location on the tablet maps to a specific pixel on the screen. The larger and more expensive tablets may not be better for coin tracing since then drawing require larger movement of hand. It is better to display parts of the coin image on the screen and look at a magnified view, minimizing the hand movements for the drawing. Choice clearly depends on application and preference.
After a bit of practice, drawing on tablet while looking at the screen is no different to drawing on paper. In fact since your hand and pen don't cover or shadow what you are drawing, and not needing to look down are distinct advantages of this setup over the very much more expensive tablet PC. You can use the pen to do all of the mouse operations as well; so you don't need to switch to mouse to select options etc. The Graphire pen with tablet is just a replacement of the mouse as the input device. You are operating within "Photoshop Elements" software so you have ALL of it's full range of image processing tools.
The top end of pen has been defined as an eraser, so you can use it
just like in a pencil. The Graphire pen activates when 5 mm from
tablet so switching between the pen and mouse is automatic. For this
reason, do not leave pen on tablet but replace it when not in use in
the molded inkpot or penholder on back of tablet.
(An advertised improvement in Graphire3 which I understand is not significantly different from older slightly less expensive Graphire2. See FAQ).
Sometime after writing up these notes I spoke with a good friend Nare Ratnapala who lectures on Art in the University of Maryland. He told me the Pen-tablet was not very popular among professional artists. The reason is interesting. If you have already trained your brain to master drawing with the pen looking at what you are drawing, it is more difficult and maybe even bad to retrain your brain to the Pen-tablet independent screen format of the Graphire. He said that even the TabletPC the screen does not the same texture of a canvas or paper; the media on which one learns to draw. It is therefore simpler for them to master using the mouse which is a different kind of device than use a pen-like instrument for which the hand has already been trained to draw on a paper. He also commented on the larger hand movements needed on the tablet as mentioned above, which is a clear case for getting the smaller tablet not just because of lower price.
For beginners like me with no prior art training I give in text below
the sequence of operations needed to draw an
outline of a coin. Menu commands are shown in Bold font with -
to indicate sub-menu option. All commands take place in the
environment of Photoshop Elements (version 1.0 provided with product).
Elements version 2.0 is NOT compatible with Win98SE
Options will be as left when the program was
last executed. So if state is in doubt or
if for what ever reason pen-tablet is not operating as expected
do Edit - Preferences - General - Reset All Tools.
In Edit - Preferences - Display & Cursors select Painting Cursors = Precise to get better control over tracing.
A 3-pixel Brush (Paintbrush Tool) gave a useful outline on 600 dpi images. Use 1-pixel on 200 dpi images. The 13 pixel default is far too wide.
Right-click on eraser on vertical tool-bar shows the choice of different erasers which are also pressure sensitive. A 5-pixel Eraser (Eraser Tool) with value selected on horizontal panel above, gives finer control over 13 pixel default which has poor control over cleaning edges.
It will probably be displayed zoomed out. One can display image at 100% using View - Actual pixels.
This is a transparent layer on which you draw and erase at will without changing the coin image. If you don't open such a layer then erase will also remove that part of coin image. Think of the layer as a transparent paper placed on the coin.
It is easy to accidentally start drawing directly on the background
image. Also make sure the new layer DOES NOT duplicate the background
coin image. Else it will not be possible to extract the line drawing
and it will remember any erase. Note that it may not seem that way
when you have both layers displayed since you see through to the
background lower layer.
The Layer should display as a cross-hatch grid which is NOT a part of the actual layer. It is just a guide and the Cross-hatch will disappear when image or layer is saved.
In Edit - Preferences - Transparency allows you to change the cross-hatch grid representing the transparent layer. Selecting Grid Size=Small gives a finer grid than Medium which is default. Grid Colors=Dark may be useful than Light which is default, if drawing mainly with a white brush.
I found a 3-pixel Brush (Paintbrush Tool) gave a useful outline
covering a minimum of coin image.
The Graphire pen width can be selected from 1 pixel to 19 pixels on the horizontal panel above. The pressure sensitive tip works almost pen-like. The color of the outline may need to be chosen based on color of coin image. Use a high contrast color (Set foreground Color) selected by bottom of such as white on coins with a dark patina or black on light silver.
Using higher magnification one can draw outline with less fine pen movements while seeing more detail. View - Zoom In and scroll to draw various parts of coin as convenient.
One can flip the line drawing in and out to see both layers or just the coin image. This is very useful to verify the line-drawing and add or edit any parts that don't line up. In this way one can get an exact tracing of the coin an not just a hand drawn illustration as often done. It is useful to always look at the actual coin under magnification to check and confirm reality of features.
These are much larger files, about 1.5 MB for 2 layers of 450x450 image. This save operation is done without confirmation. So ensure you have all of the layers as described above to save all the layers as required. It is easy to accidentally save a "Test" and overwrite and loose the original save. File - Save is too close to the File- Save As option.
Just the white line drawing with coin on displayed will not be clearly visible on a white cross-hatch background. It will be invisible if saved on a default white background. To see it CTRL-i (Image - Adjustments - Invert) to make it a black line drawing on white. Remember to change color back to white before any future line-drawing.
The line drawing can be shifted (Move Tool) on to different image of the same type of coin and scaled (Image - Resize - Scale) and rotated (Image - Rotate - Free Rotate) to match it. Resize and rotate operation may need to be done alternatively a few time to interactively get a proper registration of the features.
When moving rotating images it is useful to first View - Fit Screen to see all of coin image as well as to increase the size of the canvas (Image - Resize - Canvas Size) to be about 25% larger. This pads an additional blank border around the coin image. Remember the original pixel size so that it can be cropped back to the original size using the same option.
The operation of moving the line drawing to a new image as some useful applications.
I worried since this is a real danger of over cleaning a coin. However since I had saved a before cleaning scan I could put them back to the line drawing and shift the revised version back to the image of the cleaned coin and scale rotate it back to match drawing.
Finally however when I compared the letters to the Brahmi alphabet it transpired that the cleaned coin was much closer to the published font and the extra features before cleaning was in fact blemishes on the patina.
Wilfried Pieper who did all of the line drawing for Osmund Bopearachchi's Ruhuna catalogue commenting on this page said For all these terrible lead pieces the validity of the line drawing depends on the amount of correctness with which one is tracing the outlines of the coin designs. And this of course depends on your correct understanding and identification of the designs and legends. This is not always easy, sometimes deposits, encrustations or other artifacts can result in misinterpretations.
Text along periphery
PhotoShop has a builtin image transformation Filter - Distort - Polar Coordinates to change a circular map with Pole at center to a square Mercator Projection. This can be used to obtain a straight line image of the text along the periphery of the coin without needing to copy each letter out one at a time and rotate and position in order on a new canvas. The PhotoShop projection of circle is to a square image of the same size needs an additional horizontal stretch by π (3.14) to get very readable Brahmi text along the edge with hardly any distortion. To stretch Image - Resize - Image Size with Constrain Proportions unchecked multiply Width pixels by 1.772 and divide Height pixels by 1.772 to keep the image area the same.
Brahmi text is written anti-clockwise with feet of letters to edge.
Roman Text written clock-wise with feet of letters to the inside
would also require an additional 180° rotation of top to bottom
and left to right.
This transformation is clearly useful for presenting text written along the periphery on ancient coins in a more readable image format. Probably more useful for Brahmi text we are less accustomed to reading at different angles like we can Roman alphabet.
One needs to rotate the start point to the top of the coin image. Rotation is best done in one step to avoid image degradation. Image - Rotate - Free Rotation does not give a quantitative value to remember last rotation. Image - Rotate - Canvas Custom allows rotation by an angle input numerically. This greatly simplifies interactively selecting the angle of rotation needed to get the start point of text on top. The Canvas is increased in size and would need to be Crop Tool selected and Image - Crop back to original size keeping coin centered. Else one may cut and move a rectangular section after transformation to get the proper beginning of text.
These notes are being updated and corrected in my learning process.
Below are issues to which I am seeking the proper solution. If you know an answer please E-mail me.
A high resolution quantitative 3D image or scan of the coin could the best starting point for automated image drawing but that equipment is extremely expensive. The features of a coin need not however have the same depth and a contour plots may not highlight all of the feature. The 2D image of a scanned coin casts shadows of the features depending on the direction of illumination. These shadows can be avoided by digital photography in defuse light. However shadows do help highlight the features. It may be possible to analyze a number of images of same coin taken from different orientations of illumination and both take away these shadows and obtain an automated line drawing.
The task is more similar to 3D face recognition than 2D fingerprints which cast no shadows. However unlike face recognition all coins do not have standard design features. Large scale designs on coins are a lot more different than the set of fingerprint or set of faces. Each coin type would need to be independently setup and pre-identified. Within a single coin type it may be possible in theory to cross identify different images to find die types and varieties as currently done by eye. However any automated coin analysis is unlikely to be as good as the human eye which can do very much better qualitative feature recognition on a well illuminated high resolution coin image.
Some interesting related links
The Stylistic Analysis of Celtic Coins