Editing the Background of Coin Photos

Coin Photography – Editing the Background

There are eleven pages about photographing coins:

Black Background — White Background — Photographing the Edges — Using Extension Tubes — Choosing the Best ISO Setting — Choosing the Best Aperture — Choosing the Best Exposure — Editing the Background (this page) — Keeping Detail in the Highlights — Processing Your Image — Some Final Tweaks

Although you can use other software for this, I use Photoshop version 8.0, so my explanations are based on that. Photoshop is a big and complicated program, and this is not a tutorial; it just covers the particular tools that are useful for this purpose. I will use a tricky coin as an example - many are much easier to do than this, especially bronzes.

If you have a photograph taken with the white background technique I explained earlier, it will originally have a grey background, the colour of the original material behind the coin. The tone of grey might vary across the image depending on the position of your light source or sources – you can see in the second image below that the grey tone is darker at the bottom left. The easiest way to turn this white while not affecting your coin is to use the "paint bucket tool." This icon shares a slot with the gradient tool, so if you can't see it, click and hold on the gradient tool for a couple of seconds. When you have the bucket selected, make sure you have "Fill:" set to "foreground."

The paint bucket starts with the pixels at the very tip of the paint pouring from the bucket of the icon. It changes those, and any others like it that connect up, to the currently selected paint colour. You can select how tolerant Photoshop is about what colours are near enough to the selected one to be affected. You will need to strike a balance between too tolerant, which will paint out your coin as well, and too strict, which will only paint a tiny area next to the icon. I am using a tolerance setting of 25 on silvers with reasonable success. You might be able to do some bronzes in one sweep with a tolerance of 50. Try various settings and see how it works for you.

First, make sure you are using pure white paint by typing D to set the foreground and background to the default black and white, then click on the arrow to bring the white colour to the foreground. You might need to apply the bucket in a couple of places to remove all the background.

Even at its best adjustment, you will find that some silver coins are so close in tone to the grey background that parts of them get painted over (top right). If you see this happening, I recommend using Photoshop's quick mask mode (type Q). Using this, areas which would otherwise be painted black show up as pink (see left), and then when you return to the standard mode (Q again), they are deselected and will not be painted over by the paint bucket.

The advantages of quick mask mode as compared with, say, using the lasso tool to draw around the coin are speed and accuracy. If you have black as the background colour, select the eraser. Make sure your brush has hard edges, not soft. You can then use a big brush whose edge is almost the same arc of a circle as the edge of the coin – or at least, the part of the edge you are working on. Ancient coins are never perfect circles and you will need to change the brush size accordingly. (The left and right square brackets will do this in Photoshop.)

If only part of the coin is getting bucketed out, you only need to protect that part. Sometimes, only parts of the interior are affected, which makes using the quick mask quite simple. If it's chipping into the very edge of the coin, you need to work carefully. The edge shown on the right was quite smooth before the bucket. Maybe that won't be important if the image is going to be reduced to a small size, but maybe it will matter, and it would be annoying to only notice it after another 10 minutes of work, so it's worth having a look to see what effect the bucket has had before moving on.

When you have bucketed out the background, you will probably need to work round with the paintbrush to cover up any spots that have been left.

This page deals with creating a white background, but of course Photoshop lets you bucket in any colour you like, or even a pattern if you prefer.

There are ten pages about photographing coins:

The content of this page was last updated on 27 January 2011