Digital BW, The Print

when building curves in Photoshop for UT2/UT7 etc.. everyone seems to 
be working RGB vs. CMYK.
does RGB have an advantage over CMYK (excluding file size)?

would it not make more sense to control each color jet with its 
corresponding channel in Photoshop???

i've always work in RGB, but is it better/easier?

anyone have thoughts or experience using each for the same thing?

At 09:03 +0000 25.1.2005, evanj1969 wrote:
*******************************************

>does RGB have an advantage over CMYK (excluding file size)?

R=G=B -> neutral grey
C=M=Y=K -> ???

Martin
--

but if i'm actually printing with gray inks, or cool/warm grays, not 
color inks,  what good does having equal values of R.G.B do me? it 
doesn't mean my print will be neutral, only my photo in photoshop.

 does that make sense? after aplying an RGB curve to get the (gray) 
inks to "print" properly, the image is such a rainbow, the R=G=B -> 
neutral grey doesn't apply.

 or is there something i'm missing in you previous post?
 maybe i'm unsure of what you mean.

> >does RGB have an advantage over CMYK (excluding file size)?
> 
> R=G=B -> neutral grey
> C=M=Y=K -> ???
> 
> Martin
> --

Evan,

RGB mode provides more options for photo manipulation in PS, more 
filters, smaller file size, etc.  Also, conversion to CMYK generally 
reduces the gamut depending on which flavor of CMYK you choose.  
Probably not as big a deal for monochrome images, but picking the 
wrong CMYK in a color managed workflow could needlessly reduce 
dynamic range (you generally wouldn't want to convert to US Web 
Uncoated unless you want a lackluster inkjet print).  Most inkjet 
printers, even though they print with CMYK inks, expect RGB data 
unless you are using a CMYK RIP.  So, if you send CMYK data, the 
driver converts back to RGB so it can decide how to convert back to 
CMYK again.  Each of these conversions comes at a price.  I'm not 
sure how programs like QTR and IJC/OPM process CMYK data.

I like RGB partly because it is gray balanced, R=G=B.  If you have 
the tools and software to create your own profiles, ideally you would 
want R=G=B to display accurately and print dead neutral on paper, and 
this can be measured with a spectrophotometer.  If you achieve this, 
then you have more control and predicitability in your work.  

That being said, if you find you get better results with CMYK and 
find it more intuitive, use it.  

Lou

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "evanj1969" 
<evanj69@b...> wrote:
> 
>  but if i'm actually printing with gray inks, or cool/warm grays, 
not 

> color inks,  what good does having equal values of R.G.B do me? it 
> doesn't mean my print will be neutral, only my photo in photoshop.
> 
>  does that make sense? after aplying an RGB curve to get the (gray) 
> inks to "print" properly, the image is such a rainbow, the R=G=B -> 
> neutral grey doesn't apply.
> 
>  or is there something i'm missing in you previous post?
>  maybe i'm unsure of what you mean.
> 
> > >does RGB have an advantage over CMYK (excluding file size)?
> > 
> > R=G=B -> neutral grey
> > C=M=Y=K -> ???
> > 
> > Martin
> > --

At 09:36 +0000 25.1.2005, evanj1969 wrote:
*******************************************

> does that make sense? after aplying an RGB curve to get the (gray)
>inks to "print" properly, the image is such a rainbow, the R=G=B ->
>neutral grey doesn't apply.

The question was about advantage of RGB<->CMYK, not about printing 
greyscale and control it with RGB curves.

CMYK has one additional channel - black one. It is generated after 
conversion of RGB to CMY from pixels, where are all CMY values > 0 . 
The generation of black chanel is most sensitive part of CMYK 
workflow and "standard" CMYK profiles have black channel generated 
for ofset, not for inkjet. So if you use CMYK data in some kind of 
ofset space, the inkjet RIP or driver must konvert this CMYK to 
CMYK(mck) space for particular inkjet. And:

At 10:26 +0000 25.1.2005, ldina wrote:
*******************************************

>Each of these conversions comes at a price.


Martin
--

When you play on let say the Red channel, you play only on it, whilst if you play on M you change C and Y as well and it is virtually impossible to control. K is there because C+Y+M is not printed as deep black by our technical devices, so we help it in adding K. Read a little bit on color theory, you'll get it all.
Printing Color or Quadetones makes no difference, when you change one you change the other two.

  ----- Original Message ----- 
  From: evanj1969 
  To: DigitalBlackandWhiteThePrint@yahoogroups.com 
  Sent: Tuesday, January 25, 2005 10:36 AM
  Subject: Re: [Digital BW] RGB vs. CMYK for curves



  but if i'm actually printing with gray inks, or cool/warm grays, not 
  color inks,  what good does having equal values of R.G.B do me? it 
  doesn't mean my print will be neutral, only my photo in photoshop.

  does that make sense? after aplying an RGB curve to get the (gray) 
  inks to "print" properly, the image is such a rainbow, the R=G=B -> 
  neutral grey doesn't apply.

  or is there something i'm missing in you previous post?
  maybe i'm unsure of what you mean.

  > >does RGB have an advantage over CMYK (excluding file size)?
  > 
  > R=G=B -> neutral grey
  > C=M=Y=K -> ???
  > 
  > Martin
  > --





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[Non-text portions of this message have been removed]

> The question was about advantage of RGB<->CMYK, not about printing 
> greyscale and control it with RGB curves.
>  
> Martin


actually, that is precisely what the question was. i posted it. 
here it is again.

-------------------------------------------
when building curves in Photoshop for UT2/UT7 etc.. everyone seems to 
be working in RGB vs. CMYK.
does RGB have an advantage over CMYK (excluding file size)?
-------------------------------------------

 i was referring to the application of RGB/CMYK curves only for 
printing purposes, not asking if working in CMYK is better/worse.
 UT2/UT7 are for B&W printing. they are not "color" inks so to say. i 
was inquiring as to WHY some (or most all) choose to apply RGB curves 
after all editing is done & before printing (as opposed to CMYK). 
 this post cleared it up and answered my question.
 groups.yahoo.com/group/DigitalBlackandWhiteThePrint/message/54843

  thanks all the same for your input.
  i appreciate all who have contributed.

evanj1969 wrote:
> 
> when building curves in Photoshop for UT2/UT7 etc.. everyone seems to 
> be working RGB vs. CMYK.
> does RGB have an advantage over CMYK (excluding file size)?
> 
> would it not make more sense to control each color jet with its 
> corresponding channel in Photoshop???
> 
> i've always work in RGB, but is it better/easier?
> 
> anyone have thoughts or experience using each for the same thing?

The Epson driver knows only RGB as the input format. When you 
deliver CMYK (in any fashion) to the driver it will first 
convert it to RGB and after that apply its own CMYK conversion 
again. So there's no advantage to use the CMYK descriptions 
for B&W quad sets if you are using the Epson driver. There's 
even less transparency in what happens to the data through all 
the conversions when using CMYK curves in PS. That's also true 
for color printing with the Epson driver.

It would be nice to control each color jet (C-M-Y-K or 
C-c-M-m-Y-K(-k)) but even some commercial RIPs do not allow 
that: the "RGB" ones are like the Epson driver but there are 
also RIPs around that only use CMYK channels so the 6-7 
printers do not get a true 6-7 channel control. The special 
B&W RIPs now around are actually controlling the individual 
channels but you can't consider that to be CMYK curves either, 
they are grey + toner curves in a sense. K generation isn't a 
result of CMY amount in those curves.

I'm using a Wasatch SoftRip and have to use a kind of CMYK 
curves to get an Epson 9000 with UT in control. But I apply 
them in the RIP calibration software, the RIP gets a kind of 
greyscale images as input and the conversion is done with 
weird CMYK curves, K generation is taken out by other means

Ernst