There is something similar for B&W laser printing. Text is never 100% black, but rastered. You can digitally hide a whole lot of information in microraster on a page of printed text.
Does “rastered” mean the image is mapped onto a very fine grid and each square is given a 0-100 value for intensity of ink? I looked it up, and it seemed like the squares are given a binary value, but this is nowhere near my wheelhouse and I’m honestly not sure I understood the Wikipedia page, let alone the references
It is actually quite easy: “Black” print does not mean that 100% of all pixels are actually set. Print pixels are never perfect squares, so even if the printer only prints half of the dots, the print is still dark enough. If not, it could print 70% or 80%, but lets stick to 50% for ease of argument.
So instead of
XXXXXXXX
XXXXXXXX
XXXXXXXX
it would print
X X X X
X X X X
X X X X
For you, it would still be a “roughly black” spot (keep in mind these 8x3 pixel are 0.032mm wide and 0.012mm high on good laser printer).
Would you notice if the pattern was slightly different, like
X X X X
X XX X
X X X X
Make a bonanza of those small changes nobody can see, and you can hide thosands of bytes of data in those patterns on any printed page.
shalafi@lemmy.world 1 day ago
I believe that only applies to ink jet. You can hardly make secret dots in B&W.
Treczoks@lemmy.world 1 day ago
There is something similar for B&W laser printing. Text is never 100% black, but rastered. You can digitally hide a whole lot of information in microraster on a page of printed text.
idiomaddict@lemmy.world 1 day ago
Does “rastered” mean the image is mapped onto a very fine grid and each square is given a 0-100 value for intensity of ink? I looked it up, and it seemed like the squares are given a binary value, but this is nowhere near my wheelhouse and I’m honestly not sure I understood the Wikipedia page, let alone the references
Treczoks@lemmy.world 1 day ago
It is actually quite easy: “Black” print does not mean that 100% of all pixels are actually set. Print pixels are never perfect squares, so even if the printer only prints half of the dots, the print is still dark enough. If not, it could print 70% or 80%, but lets stick to 50% for ease of argument.
So instead of
it would print
For you, it would still be a “roughly black” spot (keep in mind these 8x3 pixel are 0.032mm wide and 0.012mm high on good laser printer).
Would you notice if the pattern was slightly different, like
Make a bonanza of those small changes nobody can see, and you can hide thosands of bytes of data in those patterns on any printed page.
user224@lemmy.sdf.org 1 day ago
Wait, I thought that’s something that only color laser do with yellow toner…