Greetings POV-Ray community,

I have been called upon to generate some hard-copy of my luscious POV-Ray
images.  I've optimized the colors of my objects and lighting to produce
vivid pictures in the on screen RGB mode image.  When I try to convert my
RGB images to the CMYK mode required by the printer, I find that much of my
image is out of gamut so the highlights look terrible and the image just
doesn't match my expectations.  Before I get into too many specifics, does
anyone have any good guidelines for what I might be able to do in either
POV-Ray or in Photoshop in order to get decent quality CMYK images?

Thanks,
Tom

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Tom Purcell wrote:
> 
> Greetings POV-Ray community,
> 
> I have been called upon to generate some hard-copy of my luscious POV-Ray
> images.  I've optimized the colors of my objects and lighting to produce
> vivid pictures in the on screen RGB mode image.  When I try to convert my
> RGB images to the CMYK mode required by the printer, I find that much of my
> image is out of gamut so the highlights look terrible and the image just
> doesn't match my expectations.  Before I get into too many specifics, does
> anyone have any good guidelines for what I might be able to do in either
> POV-Ray or in Photoshop in order to get decent quality CMYK images?

The only info source for printing I have is -
http://www3.sympatico.ca/gcircle/csbh/printingfaq.html

-- 
Ken Tyler

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In article <web.3d7d47229c874adc28f3158d0@news.povray.org>, 
hor### [at] yahoocom says...
> 
> Greetings POV-Ray community,
> 
> I have been called upon to generate some hard-copy of my luscious POV-Ray
> images.  I've optimized the colors of my objects and lighting to produce
> vivid pictures in the on screen RGB mode image.  When I try to convert my
> RGB images to the CMYK mode required by the printer, I find that much of my
> image is out of gamut so the highlights look terrible and the image just
> doesn't match my expectations.  Before I get into too many specifics, does
> anyone have any good guidelines for what I might be able to do in either
> POV-Ray or in Photoshop in order to get decent quality CMYK images?
> 
> Thanks,
> Tom
> 
> 
> 

It was my understanding that Photoshop has some sort of print translation 
thin in it. The idea is you take an image, scan it, then print a copy of 
it, scan it again and Photoshop uses the difference to adjust the colors 
so that what is printed matches what is seen on the display. I really 
wish that Paintshop Pro had that feature, since it is definitely less 
expensive to buy. :p In any case, I believe that is how the adjustments 
are made for printing the images correctly. Now where you find these 
settings, etc. I haven't a clue, since as I said, I can't really afford 
Photoshop. ;)

Now if the problem is that it is messing up the image when translating to 
CMYK, then I really am lost, but it could be that Photoshop is making the 
needed adjustments to the image to print it correctly as it converts to 
CMYK and the odd changes you are seeing is just what the printer actually 
needs to produce the correct image.

Post a reply to this message

Try this:
(I don't know the exact terms, as i don't work with english version of PS)

In the View-menu theres something like CMYK-Preview and Gamut-Warning. Turn
both on. Now you can see where there are problems. Then you can carefully
use adjustment-layers(?right?) for color/saturation and masking tools until
the grey of the gamut-warning is gone. Good think about CMYK-prewiev and
gamut-warning is that they use the current CMYK-settings, so you can change
them and see what happens.
BTW if you're using a inkjet-printer, i would stay in rbg-mode, as they will
often make better, more saturated prints if you use rgb.

greetings

Daniel

"Tom Purcell" <hor### [at] yahoocom> schrieb im Newsbeitrag
news:web.3d7d47229c874adc28f3158d0@news.povray.org...
>
> Greetings POV-Ray community,
>
> I have been called upon to generate some hard-copy of my luscious POV-Ray
> images.  I've optimized the colors of my objects and lighting to produce
> vivid pictures in the on screen RGB mode image.  When I try to convert my
> RGB images to the CMYK mode required by the printer, I find that much of
my
> image is out of gamut so the highlights look terrible and the image just
> doesn't match my expectations.  Before I get into too many specifics, does
> anyone have any good guidelines for what I might be able to do in either
> POV-Ray or in Photoshop in order to get decent quality CMYK images?
>
> Thanks,
> Tom
>
>

Post a reply to this message

I have output to very high end printers directly from BMP files that have an
RGB color space (Durst Lambda, Fujix Pictography, IRIS). The colors are
nearly identical to what I see on my monitor. Is there some conversion to
CMYK that could be done (if needed) on the way to the printer? What printer
are you outputting to?
d.

D.

"Tom Purcell" <hor### [at] yahoocom> wrote in message
news:web.3d7d47229c874adc28f3158d0@news.povray.org...
>
> Greetings POV-Ray community,
>
> I have been called upon to generate some hard-copy of my luscious POV-Ray
> images.  I've optimized the colors of my objects and lighting to produce
> vivid pictures in the on screen RGB mode image.  When I try to convert my
> RGB images to the CMYK mode required by the printer, I find that much of
my
> image is out of gamut so the highlights look terrible and the image just
> doesn't match my expectations.  Before I get into too many specifics, does
> anyone have any good guidelines for what I might be able to do in either
> POV-Ray or in Photoshop in order to get decent quality CMYK images?
>
> Thanks,
> Tom
>
>

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Thanks to everyone for their comments, here is a summary of what I've
discovered about this topic:

1) Rule 1--avoid CMYK colorspace as much as possible.  Most color computer
printers prefer to use a RGB input, even though the actual inks used are
Cyan, Magenta, Yellow, and blacK.  The printers have been factory
calibrated to convert the RGB input into a form of CMYK that is best for
the specific inks used on that printer.  Converting to CMYK actually ends
up causing the printer to first convert back to RGB and then back to CMYK
with terrible results.  At least, this is the case on the HP color laserjet
4500 and the Tectronics Phaser dye sublimation printers that we have in the
lab here.

2) I was able to get reasonable results on screen using Photoshop version
6.0 or higher, which I'm told has advanced color processing capabilites.
Again, in light of rule 1, there is little reason for most of us to use
CMYK because we're making images to display on RGB monitors or print on RGB
printers.  Therefore, unless we're graphics professionals who need to
generate CMYK images for print, this is probably not an essential upgrade.

3) The reason for original post is that I have a paper submitted for press
in a scientific journal.  Normally, the journal publisher takes hard copy
from the authors and sends it to the printing company to generate the 4
color separations for press.  Nowadays, many journals have online
submission, allowing electronic transmission of the text and figures which
they pass onto to printer directly.  Since the printer uses a 4 color image
for layout, they ask that you submit the image in the format that they
normally use, which is a CMYK EPS.  In theory, this allows the printer to
save a little time and your paper comes out faster.  In reality this is a
pretty inpractical thing because in order to generate a proper CMYK image,
you have to know the quite a bit about the settings, paper, and ink used by
the printer.  In other words, it is better in this case to generate a
really high quality hardcopy and then mail it to the printer to do the
color separation on their equipment or look for a printer that is smart
enough to convert RGB images into CMYK on their own.

Thanks for the help,
Tom

Dennis Miller wrote:
>I have output to very high end printers directly from BMP files that have an
>RGB color space (Durst Lambda, Fujix Pictography, IRIS). The colors are
>nearly identical to what I see on my monitor. Is there some conversion to
>CMYK that could be done (if needed) on the way to the printer? What printer
>are you outputting to?
>d.
>
>D.

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In article <web.3d8fa0c8bb59b30428f3158d0@news.povray.org> , "Tom Purcell"
<hor### [at] yahoocom> wrote:

> 1) Rule 1--avoid CMYK colorspace as much as possible.  Most color computer
> printers prefer to use a RGB input, even though the actual inks used are
> Cyan, Magenta, Yellow, and blacK.  The printers have been factory
> calibrated to convert the RGB input into a form of CMYK that is best for
> the specific inks used on that printer.  Converting to CMYK actually ends
> up causing the printer to first convert back to RGB and then back to CMYK
> with terrible results.  At least, this is the case on the HP color laserjet
> 4500 and the Tectronics Phaser dye sublimation printers that we have in the
> lab here.

Maybe this is the case with some bad or misconfigured Windows drivers, but
at least every properly configured Mac OS color printer driver will take
CMYK input and create appropriate results.  And it will do so on all
PostScript printers, which at least includes the HP Color Laserjets.  Of
course, what Windows does if you use a GDI printer or printer driver may be
something completely useless.....

    Thorsten

____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

Visit POV-Ray on the web: http://mac.povray.org

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news: web.3d8fa0c8bb59b30428f3158d0@news.povray.org...
> Since the printer uses a 4 color image
> for layout, they ask that you submit the image in the format that they
> normally use, which is a CMYK EPS.  In theory, this allows the printer to
> save a little time and your paper comes out faster.

Actually, it looks more like an editor problem... Speed is hardly an issue
in scientific papers, since the reviewing process itself takes months, and
scientific journals are not daily publications.
<rant> This is may be due to lack of funding (to hire competent staff) and
more generally to some unability to cope with the demands of modern data
transfer and publishing. I've been working with a scientific publisher
lately and some of their "problems" (including ones related to CMYK
conversion) only demonstrated their lack of skills with the software they
used (i.e. Photoshop and XPress). They prefer to transfer the hairy issues
to the printer or to the author instead of learning to solve them. </rant>

G.


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