
Non-photo blue - aoldoni
https://en.wikipedia.org/wiki/Non-photo_blue
======
pincubator
A discussion on "why" this is happening:

"""

The reason older photocopiers don't copy blue is very simply that the drum was
activated by reflected light from the scanner. The chemical process that
creates the "semiconductor" on the drum surface is sensitive to a fair
proportion of the light spectrum, but frequently lost sensitivity t the blue
portion of the range. Organic photoconductors had a better response to blues
but still cut off a portion of the spectrum. Newer Photocopiers (Digital)
operate differently and are dependent on the frequency range of the CCD in the
scanner, they are usually pretty good at the blues, and frequently have
settings that enable Text enhancement, enabling a setting of a contrast point,
anything darker than that point is registered as black anything lighter as
white.

"""

[http://answers.google.com/answers/threadview/id/536535.html](http://answers.google.com/answers/threadview/id/536535.html)

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jnellis
Back in the late 70's, early 80's, Dungeons and Dragons modules (self
contained adventures) used to print all their dungeon maps in light blue
because photocopy machines would not pick them up. This was effectively a poor
mans protection against piracy.

~~~
Luc
I had a manual for an assembler (Laser Genius on the C64) that used the
opposite approach: the text was black but the pages were a deep red, which
would theoretically photocopy to black.

In practice the original was about as much a pain to read as the photocopy.

EDIT: I remember the letters in the copy having a sort of lighter colour halo
around them, which made it readable. I figured was due to the blackness of the
letters pulling the limited amount of toner towards them...

~~~
jacquesm
DRM seems to have a long history of targeting their paying customers with
abuse.

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wierdaaron
Any art or writing instrument store will have gobs or pens and pencils (or
lead inserts for mechanical pencils) in this shade of blue if you're
interested. As the article states, it's good for sketches that you'll ink or
pencil over later, since they will disappear if you scan or photocopy them in
high-contrast B&W.

It sort of reminds me of the old graphics method of using RGB(255,0,255) for
sections of a sprite that should be transparent, since an alpha channel wasn't
an option, because it's such a hot pink and such a precise color it would
never naturally appear in artwork.

------
carlob
Somewhat related:

[https://en.wikipedia.org/wiki/International_Klein_Blue](https://en.wikipedia.org/wiki/International_Klein_Blue)

Also I fondly remember Hubertus Bigend's IKB suit…

~~~
tlrobinson
Apparently this is Blue Man Group blue too.

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ChuckMcM
And my engineering notebooks from the EurekaLabNotebook company use this color
for the grid which is a bit disconcerting if you make a copy of the page and
the grid disappears and you have only your writing and diagrams.

~~~
lfowles
Interesting, do you have a picture? Most engineering paper has a grid printed
only the back so it doesn't show when scanned, but I haven't seen it in blue.

~~~
ChuckMcM
These are the folks I get them from,
[http://www.eurekalabbook.com/BlueQuadEnlarge.html](http://www.eurekalabbook.com/BlueQuadEnlarge.html)
and a picture of the Blue printed one.

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jd3
As long as we're talking about shades of blue:

[https://en.wikipedia.org/wiki/Prussian_blue](https://en.wikipedia.org/wiki/Prussian_blue)

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ISL
When the article refers to 'graphics-arts cameras', what do they mean?

Is there a spectral notch filter applied to the CCD, or is the article a
troll?

"Scanning in black-and-white makes it possible for the non-photo blue still to
serve its original purpose, as notes and rough sketching lines can be placed
throughout the image being scanned and remain undetected by the scan head."

Any black-and-white scanner should have a spectrally-flat response, picking up
blue just as black and white photographs see the sky as darker than white.

It's entirely possible that older lithographic film didn't have much response
in the blue, but there's really no way that a modern imaging system won't pick
it up.

What am I missing?

Edit: Experiment is the arbiter of truth: I took a picture of the screen with
my digital SLR. As expected, every color swatch in the article is blue.
Desaturated the RAW image. Looks grey.

~~~
neilk
The "graphics arts cameras" they are referring to are pre-digital. They looked
like this:
[http://www.forgottenartsupplies.com/?what=artifacts&image_id...](http://www.forgottenartsupplies.com/?what=artifacts&image_id=178&cat=60)

The goal was to compose a layout into a single image.

You created a layout by literally cutting and pasting things onto a board.
Then you placed that board in the area at the bottom and took a picture of it
that was transferred to film loaded in the top.

You're right that the film was special; but it's the other way around from how
you were thinking. The film was not sensitive to _red_ light. To this film,
red is "black" and cyan or blue is "white".

Why this was useful:

\- You could open the box of film (it came in sheets) in a room that was
darkened except for a red bulb, without exposing it.

\- You could use overlays of transparent red material (rubylith) to mask
things precisely. Even though you could see through to the layer below, the
camera would see it as all black.

\- And, as the article mentioned you can add notes to the layout with blue
pencil and it would be invisible to the transfer. We always called this "non-
repro blue" though, as in, the camera wouldn't reproduce it.

~~~
tedunangst
Kind of strange for the info box to specify a color used in the pre-digital
era using a digital sRGB triplet.

~~~
neilk
Yeah, I expect that's just someone with a mania for Wiki-standardization. It's
not a precise shade; any cyan-ish color would do. In practice non-repro
pencils and markers varied from sky blue to a rich turquoise.

The article seems confused - it's implying that there is some magic shade of
blue that cameras can't see (even today), which is totally wrong. I think
that's why someone found it interesting to post here.

~~~
recurrie
Graphic arts film wasn't at all fussy about the shade of blue (as you note)
and so while there were expensive non-repro blue markers and pencils, everyone
I knew (at the very end of the era of graphic arts cameras) used blue
highlighters, so design studios were full of them.

I've stuck with blue as the only highlighter colour I'll ever use, more than
20 years since the original rationale.

Also, used to freak people out scribbling (non-repro) obscenities on a flat
that was going to be sent to photo and turned into a newspaper the next day.

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jtnegrotto
When I was younger I worked at a small newspaper which had only recently made
the transition from self-publishing the old-fashioned way to laying out the
paper with software and sending it off to a publishing company.

The old printing press easily took up half of our little room, and old
supplies still littered the shelves and floor. I loved digging through papers
(we had copies dating back to the first half of the 20th century) and learning
tidbits about the old way of doing things. The rest of the workers had been
there 30+ years and would reminisce about late nights spent pasting strips of
paper with text and images onto a board, annotating it with a pen that
wouldn't show up, taking and developing the photographs, and running the
press.

I don't really have anything to contribute, but it's cool to see this pop up
on here and learn a little more about it.

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danpeddle
totally off topic, but also a lovely song by the band pinback.

~~~
aoldoni
I was actually listening to the song and then searched for the name. :)

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athenot
There are certain variety of blue flowers that, when photographed, always come
out as pink. Back in the film days (with the delay to process film), it was
often the source of a mind trick. "Could've sworn that these flowers were
blue…" :)

~~~
ghaff
It apparently has to do with infrared reflectivity and even has a name:
Ageratum effect.

[http://photobotanic.com/color-shift-ageratum-
affect/](http://photobotanic.com/color-shift-ageratum-affect/)

~~~
athenot
Interesting! I thought it had to do with UV reflectivity. Thanks for the link.

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bhudapop
they still make and use non photo blue pencils in animation and comics. now a
days though they remove the blue layer with photoshop.

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percept
I made it my new HN topcolor--not bad.

~~~
Tinyyy
How much karma do you need to customise it?

~~~
percept
[https://news.ycombinator.com/item?id=438936](https://news.ycombinator.com/item?id=438936)

If that's correct, you're close(r).

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ptr
Ah, this is why some government documents need to be signed using blue ink!

~~~
jeffclark
It's more likely that they require blue ink so they can distinguish the
original from a photocopy.

