Are some fibre-tip pens invisible to scanners?

[Cleggy]

When I'm trying to troubleshoot some fault, I often mark up a copy of a circuit diagram with coloured pens to help "see the wood among the trees" (red for the positive line, green for signal, blue for AGC, etc.). I've just bought some new fibre-tip pens for this purpose, and although they are very bright to look at directly on paper, my Cannon scanner (set on 'colour', 400dpi) barely detects them. It's working fine on other coloured sources. I've never seen such an effect before - anyone else?

Cleggy

[Refugee]

That can happen. The dye in the pen must be in a dead spot in the light spectrum of the LEDs used in the scanner.

[boater sam]

Lots of problems scanning or copying some shades of blue especially for some reason. I find it hard to print £5 and £20 notes! Would be nice if I had one to copy some days.

[Murphyv310]

Lots of problems scanning or copying some shades of blue especially for some reason. I find it hard to print £5 and £20 notes! Would be nice if I had one to copy some days.

Hi.
Sam you must have a scanner that isn't up to the mark.
the £20 notes I scan come out fine and the shops take them fine even though nothing is on the back

[ppppenguin]

Many scanners and image manipulations software will prevent you scanning and editing banknotes:
http://www.telegraph.co.uk/technology/ad...knote.html

[boater sam]

Before the armed men in uniform bang on my door with the big red key, I will admit I was only joking.

Strange that you can print photographs in full colour but scans and copies change the tones.

[ppppenguin]

An awful lot of technology goes into making the colours you see on the screen and in print look even approximately right. For a start there's a vast amount of hassle going from RGB (CRTs etc) to CMYK (printing) all with different colour gamuts and making it work tolerably well. To make it work really well is even harder.

[Nick]

https://en.m.wikipedia.org/wiki/Printer_steganography

Modern laser printers have secretly encoded tracking information ( printer serial number and date/time etc.) on every page printed for many years. This is to enable the security people to track forgers etc.

It's well documented...

[ppppenguin]

In the old days of the Soviet Union every typewriter had to be registered with the authorities. This isn't so very different. Except that our MI5 would never dream of abusing such information.