Re: Gum Color Gamut & Beyond CMYK?

[Jacek Gonsalves <jacek@jagnight.com>]

Hi,

Thanks for the link David, that really is quite intresting. Will  
contact herbhoover and ask him how he did it...

Yves, I understand that on a monitor screen there are always out of  
gamut information being displayed. Though its a matter of  
understanding between what color space your monitor holds and the  
image your using.
My own initial creativity stems from the digital image and gum  
printing is the final product, that I want to retain the same detail  
and color(dependent on different color space of course) from my  
digital file.

http://www.colblindor.com/wp-content/images/CIE%201931%20color%20space.png
The above link shows a CIE colorspace, what the eye can see.
Say I want to use a color at very top end, the green part where 520  
is. How could I do it? For a print I would need to find a pigment that  
matches that green? Come up with additional separations? Though you  
could argue that the image I use needs to have that green in it. This  
is where photoshop comes in, where you can tweak or increase the color  
to match that 520.
I'm more intrested in matching my colors between what is on screen and  
what is the result on my print.
Though in some ways I tend to agree with Katharine, that there might  
not be any reason to go a 6 separation route, if you were to choose  
vibrant colors in your 3 separation, CMY or RGB mix, I could possibly  
get that 520 green...
A tool to find the exact the colors from screen to print is Datacolor  
Spyder printfix tool. For around $300-$400, you can get LAB and  
Density values from your print. Therefore I am able to plot what color  
space my prints fall under.

Cheers
Jacek

----- Forwarded message from davidhatton@totalise.co.uk -----
    Date: Sun, 21 Sep 2008 07:16:23 +0100
    From: davidhatton@totalise.co.uk
Reply-To: alt-photo-process-l@usask.ca
 Subject: Re: Gum Color Gamut & Beyond CMYK?
      To: alt-photo-process-l@usask.ca



  Hi,

  Take a look at this photostream in flickr

  http://www.flickr.com/photos/herbhoover/422834327/[1]

  It's exaccerlly what you're talking about

  Regards

  David H

On Sep 21 2008, Katharine Thayer wrote:

See my page on tricolor gum printing

http://www.pacifier.com/~kthayer/html/tricolor.html

for a brief consideration of this topic (scroll down the page to the
subheading, "Is it possible to reproduce the entire spectrum using
three color layers?" )

The answer, from Bruce McEvoy, is no, you do need to add the
secondary colors (in other words, in gum printing, use six layers
including the secondary colors in addition to the primary colors, in
order to produce accurate colors throughout the spectrum, and I
suppose some sort of profiles as Jacek suggests might be the way to
generate the color separations for the secondary colors. But this
seems to me an enormous effort and possibly a misplaced effort to
boot; if you're looking for this kind of color precision, gum may not
be the right process for you. Not that I would discourage anyone
from dedicating themselves to this kind of study if it appeals to
them, just that for me and my house, I don't quite see the point.

However, the purpose of the extra colors and separations, as I
understand it, is not to extend the gamut so much as to refine it.
Depending on the pigments you choose as primaries, the layered color
mixtures will produce different palettes of greens, oranges and
purples; generally when printing tricolor we pick three primaries
that give us the kind of secondary mixtures we want. For example, I
generally prefer ultramarine or prussian blue for tricolor because I
don't like the greens that pthalo produces with almost any yellow,
they look unnatural to me, and since I print a lot of landscapes with
trees/leaves, I want a more natural looking palette in the greens.
Adding the secondary colors to produce six layers will theoretically
make it less necessary to pick and choose primary pigments to produce
the kind of secondaries you want, because you can choose the
secondaries to your liking. But like I said, this seems a heck of a
lot of work, when three colors, chosen carefully, will almost always
give us a palette that gives us a reasonable enough approximation of
realistic color, with special attention to producing the secondaries
that we're most interested in.

Katharine

On Sep 20, 2008, at 9:11 PM, Jacek Gonsalves wrote:

> Hi all,
>
> Just continuing what Loris was talking about in regards with using a  
> predefined set of pigments and building a profile for Gum printing.  
> If one could build the profiles based on the CMYK pigments, can we  
> say that this holds a certain color gamut. Lets say we want to  
> increase the color gamut?
> There are other methods as Pantone Hexachrome method of 6 color  
> separations CMYKOG, adds orange and green separation. Adding these  
> additional separation would therefore increase the color gamut. That  
> is if the image you have includes those additional colors.
> I'm sure there are methods to make additional separations in PS,  
> though it might be complicated? If someone knows how to do this  
> please chime in..
> Though it excites me to think that one could increase the color  
> gamut from finding what pigments fall further than the usual inkjet  
> printers do these days.
> Regards
> Jacek

Links:
------
[1] http://www.flickr.com/photos/herbhoover/422834327/


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