Why Print using sRGB color space?
Michael Hopper
digital color printing. As I see the current laser printer market
almost all the devices try to match the color space of the commercial
CMYK printers. Now I see a new 65 page per minute laser product from
Konica that purports to print almost all of the sRGB color space with
four toners (one of them black). The prints seem to have a much
expanded blue/violet/purple and also greens than you can print with
the standard CMYK sets.
My questions are
1) Does printing with sRGB make anything easier (removing some color
management for example)?
2) What is require of the toner to get this behavior? More
transparent toners? Pigments that absorb less in the gion outside the
desire color? Whatever?
Mike
Thomas Richter
> I am a not a color scientist only knowing a little about operational
> digital color printing. As I see the current laser printer market
> almost all the devices try to match the color space of the commercial
> CMYK printers. Now I see a new 65 page per minute laser product from
> Konica that purports to print almost all of the sRGB color space with
> four toners (one of them black). The prints seem to have a much
> expanded blue/violet/purple and also greens than you can print with
> the standard CMYK sets.
>
> My questions are
>
> 1) Does printing with sRGB make anything easier (removing some color
> management for example)?
No printer prints "in" sRGB. sRGB is an additive color space, meaning
each color is the additive mixture of three primaries, red, green and
blue. However, printers generate colors by dyes, not by mixing light
(directly), and thus operate in a multiplicative color space, which is
typically CMYK (or something related, using more dyes).
What Konica is likely trying to say is that their printer can generate
most (or a larger percentage) of the sRGB gammut, meaning, of all the
colors a standard sRGB monitor can generate (which is by itself again a
pretty small gammut).
It makes things in so far easier as monitors usually operate in sRGB,
and you don't "need" an additional color management - whatever "sRGB"
should mean for a reflective medium like paper where colors depend on
the illumination of the medium (a situation not present for and covered
by sRGB). However, this is part of any usable tool chain for printing
anyhow, thus might be part of the printer driver here.
> 2) What is require of the toner to get this behavior? More
> transparent toners? Pigments that absorb less in the gion outside the
> desire color? Whatever?
I'm not a color expert either, but the problem might be that the shape
of the gammut you can generate by multiplicative mixture is rather
different than the triangular shape of additive color mixing. Which
means that the primaries you use for mixing must be rather extreme at
the edges of the xy-"horseshoe". The second problem is that the sRGB
gammut gets smaller for very light colors and is large for rather
mid-range colors, whereas CMYK has by construction the largest gammut
for light colors, a second mismatch. Usually, you would want to correct
by that by either adding lighter dyes ("photo Y" etc) or by having a
technology that spreads the dye so lightly over the page that you still
cannot make out the dithering pattern - probably that is what Konica
announces.
Note that all these are "necessary" conditions, not "sufficient"
conditions, from my lay men's perspective.
Greetings,
Thomas