Sorry not to have replied sooner - some family (non-tree) stuff to sort out!
Many thanks for all the suggestions. I will work through them and report back.
So far, I have tried the "two rotated scans overlaid" tip from Tim. This has worked reasonably well - about 85% better.
Will keep trying and let you know.
Results 11 to 13 of 13
27-01-2011, 11:03 AM #11
- Join Date
- May 2008
- West London
02-12-2018, 6:07 PM #12
- Join Date
- Dec 2018
As you initially noted, the texture reflects light from the scanner and this is due to the way scanners work. As the light passes the photo's surface it reflects off each tiny dot - a specular highlight (like a mirror). There are at least three ways to correct this - two with the scanner, one with a camera.
As one poster noted above, you can perform two scans rotated 180 degrees to one another, then combine them using Photoshop or something similar applying the Scripts > Statistics > Mean. This effectively removes what is not common to both photos. Helps for creases and deep scratches too.
Next is to use the Descreen function found somewhere in your scanning software (Vuescan has this on an Advanced options page on the Filter tab). This can get tricky unless you know the characteristics of the texture - screen angle and screen frequency - how many dots / lines per inch and the angle relative to one edge. 45 degrees and 75 lines is pretty common. Try to get the photo as square as possible on the scanner. Descreen only works with textures that have a regular pattern, not rough finishes, that's when you use option one. Works pretty well.
Third is the most fiddly, and uses a camera, two lights sources, and polarizing filters - known as the crossed polarizers technique. Identical light sources are placed on either side of the image and each is covered by a polarizing filter (usually a plastic sheet) oriented the same way, i.e., they pass light when one is laid over the other. Polarized light illuminates now the image. The camera is positioned directly over the image and it too has a polarizing filter on the front, but this one is oriented 90 degrees to the lights' - it looks black when pointed at the lights. This trick blocks polarized light reflections that are rotated by the surface finish - removing the dots - more-or-less. This technique also works for rough textures and silvering or mirroring on really old photos.
Last, and this is for advanced users, you can use an FFT (Fast-Fourier Transform - fancy arithmetic) to reduce / remove the dots / lines. One plugin that's available only works in 32-bit Photoshop, on 8-bit, RGB images. So if you have anything else you need to convert it to those specs first. Even B&W images - just convert them to RGB before stating the FFT.
the link 32-bit PS only: 3d4x.ch/Swift's-Reality/FFT-Photoshop-plugin-by-Alex-Chirokov/16,35[/
and another one for 64-bit PS: rognemedia.no/
Last edited by Lesley Robertson; 03-12-2018 at 9:20 AM. Reason: URLs deactivated, copy & paste to use
03-12-2018, 9:22 AM #13
Welcome to the British Genealogy Forum. Did you notice that you have joined an extremely old thread?
Our TOC does not allow the posting of active threads or emails, so I have edited the urls to your blog at the end of the message.
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