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Non-photo blue

en.wikipedia.org

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Re: Non-photo blue

#11

Post by ghaff »

ISL wrote: post #2

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 ha…

The article does mention diddling with the contrast and brightness as well as desaturating it. However, it doesn't give references to digital-based workflows working like this. I associate non-repro blue grids and pens with doing physical paste-up on a light table. I wouldn't think they'd be part of a typical digital flow although someone in that business would know better than I.

[Edit: As someone wrote, the article just seems confused. Yeah, you can adjust a digital B&W image so that a light blue goes away. You can also adjust it so a light yellow or a light anything goes away. Digital sensors do have different wavelength sensitivities but the use of non-repro blue and rubylith were a function of the specific sensitivities or lack thereof of litho film.]

Re: Non-photo blue

#13

Post by neilk »

tedunangst wrote: post #9
neilk wrote: post #7

Earlier quoted context omitted.

The "graphics arts cameras" they are referring to are pre-digital. They looked like this: http://www.forgottenartsupplies.com/?what=artifacts&image_id... 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 righ…

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

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.

Re: Non-photo blue

#14

Post by 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

Re: Non-photo blue

#15

Post by TazeTSchnitzel »

ISL wrote: post #2

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 ha…

The article was written first in 2005. Back then, digital photography was not so popular. :)

Re: Non-photo blue

#16

Post by 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.

Re: Non-photo blue

#17

Post by Luc »

jnellis wrote: post #16

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.

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...

Re: Non-photo blue

#19

Post by davidpardo »

jnellis wrote: post #16

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.

And Hewson Consultants did the same in their "interactive video adventure" Avalon circa 1984. The game -for the Sinclair Spectrum- asked for a four digit code printed in non-copy blue that came in the box. Quite a few games would do the same later, like Larry's, monkey island or Elvira, Mistress of the dark, with different approaches, but Avalon's was pure blue over white paper.

Re: Non-photo blue

#20

Post by pizzeys »

TazeTSchnitzel wrote: post #15
ISL wrote: post #2

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 ha…

The article was written first in 2005. Back then, digital photography was not so popular. :)

Apparently you remember a different 2005 to me!
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