My father was a graphic artist, so I am familiar with the invisibility of certain shades of blue pencil to process cameras.
However, there’s a new twist: My auto insurer only sends me one wallet card, and rather than request a spare every year, I simply slapped them on my computer scanner and ran off a copy for the glove box to make displaying it easier and for the benefit of anyone else driving my car; the other went into my wallet to cover me when driving anyone else’s car. (Hereabouts, the inability to show one on demand can get you towed.)
But about a year ago, the scanner stopped seeing the blue ink on the cards, like it was invisible, and no amount of fiddling could bring it out. It sure looked the same to my eye, but not to the scanner. An effective anti-counterfeit measure, to be sure, which impressed me as most clever, as the difference was not at all apparent until one tried to snag an image. (Sure wish something similar had been sufficient for our currency, instead of turning it into Monopoly money.) I’ve also noticed a variation of this technique is apparently employed on prescription pads, as a blue-patterned background has appeared on them in the past few years.
Welcome to SDMB, jefferykopp! Since you have started this thread in Comments on Staff Reports, a link to the specific staff report we are discussing would be useful. Could it be this one?
I’m trying to figure out why an insurance company wouldn’t want you to make a copy of their card. Mine (State Farm) sends me 2 copies for each policy and it is printed in red and black, making it very copyable.
If selenium sees only blue and blue-green, wouldn’t it be blind to red, black and other colors? Isn’t this a mistake? Shouldn’t the line be “selenium is blind to blue and blue-green…”?
Nope. Both people and machines don’t see darkness; they see light. Therefore, if you can only see blue, you can’t tell the difference between blue and white.
Re: Straight Dope Staff Report: What’s up with ‘no copy blue’?
Quote: “Early silver halide-based photographic systems were orthochromatic, meaning they were blind to all visible light except blue.”
Correction: Early silver halide-based photographic systems were color-blind.
Quote: “That problem was solved in 1906 with the introduction of panchromatic film, which reproduced every color with the correct gray value.”
Correction: "That problem was solved in 1906 with the introduction of orthochromatic film, which reproduced blue and green with the correct gray value.
Re: panchromatic film:
(by asbjxrn on reddit.com - Reddit - Dive into anything)
“Panchromatic film was invented in Dec 1912 and did not take over popular photography as THE choice until the 1960’s. Orthochromatic film stock—the only kind previously available—had good reproduction at the higher frequency (blue) end of the colour spectrum, low response to yellow and green and complete insensitivity to reds.”
Quote: “. . . non-photo blue (cyan) has the advantage of standing out well to the human eye while being easy to turn off, since it’s one of three additive primary colors. . .”
Correction: Cyan is a pale-blue/green dye color that’s one of the three subtractive colors (the other two being yellow and magenta). Red, green and blue are the additive colors.
Right. Remember that white is composed of all colors of light, including blue, so a reaction requiring blue light will work the same for white light. So, the way it works is this:
The selenium on a copier drum reacts to blue light by losing its charge so toner doesn’t stick to it. Other colors don’t affect the selenium so the toner sticks. This process produces a positive image.
In photography crystals of silver salts suspended in gelatin are modified by exposure to blue light. The developer selectively reduces the exposed crystals to pure silver. The fixer washes away the unexposed crystals, leaving behind the opaque silver. This gives a negative image, in which pure blue and white created black and all other colors created clear. However, very few colors in nature are pure, in that they reflect no blue light at all, so it was a while after the invention of photography before anybody realized the process was colorblind. Modern, if that can be used to describe a process that is quickly becoming obsolete, graphic arts film is “high contrast,” meaning it’s not particularly sensitive so it takes great, honking amounts of blue light to cause the reaction. The piddling amounts reflected by other colors are not enough so there are no gray tones.
Also, in an effort to forestall Disney lawsuits, I need to correct the report that was sent out. The animated feature was One Hundred and One Dalmatians and the live-action feature was 101 Dalmatians. The second use describes a number of dogs, not a title. The corrected sentences will read:
Frank, we’re both wrong, though you are much moreso ;). The original emulsions were monochromatic and sensitive to only blue light. Orthochromatic film, was invented in 1873 by Hermann Carl Vogel. When he added certain light-filtering dyes to the emulsion he added green light to the pallette. This made landscapes more realistic but the emulsions were still red-blind. This problem was solved to a greater or lesser extent by others but fully panchromatic emulsion for photographic plates was not produced (by Wratten & Wainwright) until 1906. Orthochromatic film was not driven out immediately, though, since manufacturers hate paying licensing fees, but panchromatic film owned the market long before asbjxrn’s 1960s because it rendered skin tones so much better. (C’mon, you’re using an anonymous comment on a site devoted to photos of bathing beauties as a reference?)
As for the additive/subtractive business, “additive” was not in the report I submitted. However, I refer you to Cecil’s caveat regarding Staff Reports:
I will submit a re-write incorporating your correction and hope it gets changed before the official release date (Tuesday), though I’m more intent on getting the Disney thing worked out. Disney scares me.
Panchromatic film was certainly the norm when I was a kiddywink in the 1950s. However, orthochromatic film continued in professional use at least into the late 1970s (and perhaps much later, for aught I know to the contrary) for portraits of men–but not women, because “character lines” in men are “age lines” in women.
As I recall (keep in mind I’m generalizing), orthochromatic film was still in use 'way into the '60s and beyond in what is referred to as “process photography” and “advertising art,” where the terms “color separation” and “masking” were used. With filters, this allowed product box and bottle labels to be photographed in black-and-white so that sharply defined characters could be maintained and enhanced while the blue-line markings could be dropped out.
I’m sure others would have more pertinent information on this subject.
Yeah, with green filers for the men and pink ones (with Pan) for the ladies! And maybe a bit of Vaseline on the filter if the lady was still showing too much “character.”
Oops, that’s right; dropped the link while mashing about logging in.
I presume to keep people from “recycling” expired insurance cards by editing the image of one.
It’s an elegantly subtle technique, probably exploiting some deficiency in the light tube/sensor combination common to consumer scanners, though to be sure, I’d have to fire up an oooold model to see if some provision was built into this one to accommodate such anti-counterfeiting measures.
I recall a couple decades ago, a chocolate-colored ribbon (Selectric?) was developed to be used on darker brown paper, to frustrate photocopying. It was awkward.
I also read that the first office Xerox (the one with the curved glass and the three knobs) made a slight reduction; it was said to be done out of some concern over copyright, though I later wondered if that was just a story to cover a design limitation. But I’m old enough to recall that over time, recopied phone lists would gradually shrink in size (this model remained in common into the early 1970s).
Not really.
To defeat it, all you have to do is place a transparent colored plastic sheet over the page before putting it on the scanner.
These were fairly common back when scanners & copiers were more sensitive to ink or paper colors. We used to have several, that were stored next to the office copy machine. As I remember, they were mostly a yellow color.
Sorry, I don’t get this, but maybe we’re arguing over semantics.
I can “see” blue with my baby-blue eyes. That means that the color blue causes a change in something in my eye/brain network that I call “blue”.
I cannot see ultra-violet.
So I can see blue, but am blind to ulta-violet.
If a selenium drum sees blue, it would cause a change in something. If it is blind to blue, it would not. My experience with selenium-based copiers is that a light blue original document causes no image to appear on the drum or the output copy. But red or black on the original causes a (latent) image on the drum and shows on the output copy due to the application of toner.
So I would conclude that selenium drums are blind to blue but sensitive to red and black; hence my challenge to the Staff Report.
Your reasoning would be correct if we were talking about blue light against a black background. We’re talking, instead, about blue ink on a white background. The blue ink, at least approximately/ideally, reflects just as much blue light as the white background does. All the blue ink does is remove non-blue wavelengths. So, if you detect only blue light, you can’t tell blue ink from white background.
Orthochromatic emulsions are still standard for B&W photographic paper. For that it’s fine to be sensitive to just part of the visible spectrum (there’s no color variation in the negative or the light source), and it permits the use of a safelight in the darkroom (filtered light that doesn’t contain wavelenghts that the paper is sensitive to, and lets you see in the “dark” room).
Whaddya know, a non-glare sheet protector does it (through both sides, but not slipped inside). While in your case the color was involved, I believe this must involve the angle of reflection off the ink-paper combo.
I used to know a bit about lithography, so I find this fascinating.
P.S. After years of struggling to de-screen halftoned photos using various blurs, I finally discovered “edge preserving smooth” (in Paint Shop Pro 8, buried under Adjust->Add/Remove Noise), which I wish I’d found long ago. I wonder what the equivalent is called in PhotoShop?
Ah, another person who’s confused when a gamer talks about his PSP! Weren’t too many games you could play with Paint Shop Pro.
Owning an IBM Microchannel-type computer, I was confused when an earlier generation of PlayStation users talked about their PS2s. I wondered where the PS/2’s slash had gone.
(Waiting for somebody to link me to hot Model 70P on Model 77 action. Everything else is on the internet.)
That means that the color blue causes a change in something in my eye/brain network that I call “blue”.