Converting The Diameter Of A Coin Into Pixels

Your reply was split into its own topic for the proper attention.

Reference topic: http://goccf.com/t/275520

There is no direct conversion, but what you are actually asking is covered in rmpsrpms's answer above.

A pixel is a measurement on the display, it does not have a physical mapping except for that model of display. You will also see them quoted in dpi (dots per inch).

A 16:9 27" 1920x1080 display has a panel size of 27" diagonal or about 23.5" wide and 13.2" high.

1920/23.5 and 1080/13.2 gives you that each pixel on the display is 0.12257" square (actually a little less because there is a small border).

If you want to print an image that is say 4x6 at 100dpi, you need 400 x 600 dots.

There are also printer's measurements, points, ems, picas, etc. A point is 1/72" (or 72 points to the inch).

While your graphics program can deal with one or more of those, it's primarily to produce scaled & camera ready images.


Your computer maps dpi to / from pixel size internally. (If you get deep into Microsoft Windows, many measurements are internally in pixels, some in points, other in twips (1/1440") - different APIs expose different things).


For example a point is 1/72".

You should be able to use an editing program to crop the coin to a square image. Do that for both. Let's say that the result is one of the images is 1040 pixels square, and the other is 826 pixels square. This will give you a ratio of 826/1040=0.79423. Use this number to reduce the original (larger) image so the coin will be the same size as the smaller one. If the original image is 1800x1200, reduce it to approximately 1800*0.79423 x 1200*0.79423 or 1430x953. Then you can use that image with the original (smaller) image for overlays.

Very nice work RMP! our local math wiz