What do you use CMYK mode for?

[Jesper]

I have the book Mastering Digital Printing (http://www.amazon.com/exec/obidos/tg/detail/-/1929685653/qid=1081944280/sr=8-1/ref=pd_ka_1/002-0076724-3541634?v=glance&s=books&n=507846), which is very interesting if you want to know all about printing.

But one thing it doesn't really explain, is what Photoshop's CMYK mode is so useful for. I know what it is - your image is separated into cyan, magenta, yellow and black, the inks that printers use.

In another post (http://photography-on-the.net/forum/showthread.php?t=29807) in the Canon EOS Digital forum, evilenglishman says:

don't forget that PSP can't handle CMYK properly - this is essential for any professional who is producing artwork/graphics/photos for print.

Why is it essential?

[scottbergerphoto]

I'm going to step out on a limb here, as someone like Roger Cavanagh would probably give a better answer, but as far as I know, CMYK is usually reserved for professional graphics houses. Most if not all inkjets use RGB and if you use CMYK, it will have to be converted to RGB for printing. I hope that helps until some who knows more comes along.
Scott

[Scottes]

I'm going to step out on a limb here, as someone like Roger Cavanagh would probably give a better answer, but as far as I know, CMYK is usually reserved for professional graphics houses. Most if not all inkjets use RGB and if you use CMYK, it will have to be converted to RGB for printing. I hope that helps until some who knows more comes along.
Scott

Close enough IMHO. CMYK is the standard 4-color printing inks used by presses and professional printers. Cyan, Magenta, Yellow, and Black. Though these are the same colors in use by many (all?) inkjets, the inkjet drivers are specifically made to convert the RGB computer colors to CMYK.

A big issue with RGB-to-CYMK is that the two spaces are radically different as one is additive (add all colors to get white) and the other subtractive (remove all colors to get white). Add to this the fact the 100% Cyan + 100% Magenta + 100% Yellow does not yield black but rather a fairly muddy brown. So the black is mixed in using a process known as undercolor removal. Based on the final shade desired, a percentage of each/any CMY is removed and black is added in place of these. This process is pretty precise and is highly dependent on the inks and paper being used, but any RGB-to-CMYK conversion will do some sort of undercolor removal.

Undercolor removal could be considered an art by some - I've seen fairly heated arguments over calculations which yielded an identical color according to a spectrophotometer. And I've had the process explained to me by a god-awful brainiac multi-PHD scientists-type - for what seems like a simple process this guy practically had me in tears because I couldn't understand. Maybe I was just young then, who knows? Granted, that was just at the advent of computer printing and computers do a lot of that work now, so it's probably much easier.

So we can see that the process of converting RGB to CMYK is fairly complicated and rather exacting. Computerization makes it's simple but it all depends on who wrote the program and algorithms. If a piece of software does a lousy job of undercolor removal it's going to be a nightmare to fix when printed.

Therefore it's essential to handle CMYK properly.

IF you care about printing to a 4-color press. Most of us don't care - inkjet printers and the types of printing houses who cater to digital photographers are geared to handle the RGB-to-CMYK conversion quite well. But those people who print to 4-color presses and depend on this for their job will certainly care. Those people can notice color shifts that most of us can't see. And the big 4-color presses are much more exacting to boot.

But if you didn't already know most of the above then you probably don't care about CMYK in any way, shape, or form. Those who do care about CMYK know it, and they use Photoshop. (Probably.)

[evilenglishman]

The CMYK colour mode is used in the printing industry.

This is nothing to do with home printers (which will print CMYK images as well as RGB).

As an example lets say you took a ****-hot photo of a car race with you D-SLR. A car magazine says to you, we want to buy it to put in our magazine.

In most cases they would accept your RAW or JPEG, which they would have to convert to CMYK (and usually a tiff).
There may be occasions where you are required to proved a CMYK image, and you wouldn't be able to do that in PSP - I think you can export channels in CMYK but there is no on-screen mode.

CMYK - Cyan, Magenta, Yellow and Key (black) ar needed for printing as most printing is done this way.
Other methods include spot colours which are generally more vibrant and are pre-mixed. An example of this would be a really vivid orange colour that just couldn't be reproduced with CMYK, you would have to specifiy its specific number to the printer. You would also need to create a seperate channel in your image to define where this would be printed.

Scott is incorrect when he says most inkjets use RGB.
How many printers come with 4 seperate colours? Most come with CMYK. I haven't seen many with only three colours RGB. Look at your cartridges.
Images should not need converting to RGB either.

Generally if you just put your images on the web or print at home or even get photographic prints you wouldn't need to bother with CMYK. But there may come a time when you might need it.

[Sam North]

Also, by splitting the colour channels - RGB (or CMYK) - you can get results very similar to conventional filters for black & white film photography.

[maderito]

Scott is incorrect when he says most inkjets use RGB.


This point should be clarified so as not to confuse people.

Desktop inkjets accept RGB image data and internally convert it to a version of CMYK that is specific to the types and number of printing inks used. So, you don't have to - nor should you - submit a CMYK image to an inkjet printer. Just prepare the image in a standard RGB color space and ship it to the printer.

[Scottes]

Scott is incorrect when he says most inkjets use RGB. How many printers come with 4 seperate colours? Most come with CMYK. I haven't seen many with only three colours RGB.

I didn't say that.

"Cyan, Magenta, Yellow, and Black. Though these are the same colors in use by many (all?) inkjets, the inkjet drivers are specifically made to convert the RGB computer colors to CMYK. "

and

"...inkjet printers and the types of printing houses who cater to digital photographers are geared to handle the RGB-to-CMYK conversion quite well."

How did you get that I said "most inkjets use RGB" ???

[evilenglishman]

...Most if not all inkjets use RGB...
Scott


errr, thats how I got it - I never mentioned you :D

[Scottes]

...Most if not all inkjets use RGB...
Scott


errr, thats how I got it - I never mentioned you :D

Oops, sorry. I forgot that Scott posted. And I forgot that there are others named Scott besides me.

[stopbath]

I have the book Mastering Digital Printing (http://www.amazon.com/exec/obidos/tg/detail/-/1929685653/qid=1081944280/sr=8-1/ref=pd_ka_1/002-0076724-3541634?v=glance&s=books&n=507846), which is very interesting if you want to know all about printing.

But one thing it doesn't really explain, is what Photoshop's CMYK mode is so useful for. I know what it is - your image is separated into cyan, magenta, yellow and black, the inks that printers use.

In another post (http://photography-on-the.net/forum/showthread.php?t=29807) in the Canon EOS Digital forum, evilenglishman says:

don't forget that PSP can't handle CMYK properly - this is essential for any professional who is producing artwork/graphics/photos for print.

Why is it essential?

It is essential when you print in four colours on a printing press. When you print to your desktop printer, the printer will output one sheet of paper with all the inks done in one pass.

The CMYK file is need as the printing press uses the Cyan to print the cyan plate, then the Magenta to print the magenta plate.... All four are then registered and printed on paper (one impression per colour) in four passes.

[scottbergerphoto]

evilenglishman wrote:
"Scott is incorrect when he says most inkjets use RGB.
How many printers come with 4 seperate colours? Most come with CMYK. I haven't seen many with only three colours RGB. Look at your cartridges.
Images should not need converting to RGB either. "

Actually, I'm not incorrect. I was talking about the instructions/file that you send to the printer. You don't have to convert your RGB data to CMYK.
I use the Epson 2200, a 7 ink printer. If you work in CMYK in Photoshop, the Epson RGB Printer Driver requires that you convert the file to RGB before sending it to the printer.

I also found this post:
http://www.usask.ca/lists/alt-photo-process/2000/mar00/msg00373.html
Re: CMYK-RGB conversion (was: Epson or HP for alt-phot

--------------------------------------------------------------------------------

To: alt-photo-process-l@sask.usask.ca
Subject: Re: CMYK-RGB conversion (was: Epson or HP for alt-phot
From: Katharine Thayer <kthayer@pacifier.com>
Date: Thu, 23 Mar 2000 11:50:50 +0000
Comments: "alt-photo-process mailing list"
References: <63.335877d.260a506a@aol.com> <01JNCDE7BOF09OIWP1@sask.usask.ca>
Reply-to: kthayer@pacifier.com
Resent-message-id: <0FRW00CIV4ACFI@duke.usask.ca>
Resent-reply-to: alt-photo-process-l@sask.usask.ca

--------------------------------------------------------------------------------

Mitch Valburg wrote:
> If you print using a CMYK RIP (EIEIO?) then you have full control
> over the four ink channels, bypassing the printer driver. This is also the
> only way to directly or precisely control the amount of black ink laid down,
> since even CMYK files sent directly from Photoshop are converted by the printer
> driver back into RGB before printing.


For those for whom the implications of the above are not immediately
obvious, I'd just underscore Mitch's comment by adding that converting a
CMYK file back to RGB is not a benign act; in this conversion
information is almost always lost from the file. This is why you should
send an RGB file rather than a CMYK file to most inkjet printers unless
you have a CMYK RIP installed, because as Mitch said, otherwise the file
will be converted back to RGB and then to the printer driver's CMYK
space. Since information is lost in the CMYK-RGB conversion, the
resulting CMYK file will be different from the original CMYK file, even
aside from the added complication of the possible differences between
the Photoshop CMYK space and the printer driver CMYK space. Staying
within Photoshop for sake of simplification, if you start with an RGB
file, then convert that to CMYK and later back to RGB, the resulting RGB
file will be different from your original RGB file, because information
from the original file will have been lost in the back-conversion. And
by extension, if that corrupted RGB file is then re-converted to CMYK,
it won't be the same as the earlier CMYK file. This is why there is a
feature in Photoshop that allows you to see what an RGB file would look
like in the CMYK space you have specified, without actually making the
conversion.
Katharine Thayer

I said I was going out on a limb, not out of my mind 8)
Scott

[ryuwulf]

on a side note which is open for debate. CMYK is "sometimes" preffered when color correcting an image.

RGB being what most "basic" peeps use. Well when tweaking in your curves or levels sometimes you cant get the right color.

If all else fails convert the image to CMYK and tweak.
Why???

You now have 4 channels to work with instead of 3. Most notably the K channel for blacks.

I used this with some decent results. Point being you now have more options to work and tweak with instead of 3.

i wont go into the whole print shop bit, but I hope this adds a little more to your question

books that ive found most helpful in understaning the color process:

Photoshop Color Correction (this guy is a nerd, but a very smart nerd with great technical knowledge, highly reccomend)

Retouching and Restoration PHotoshop (great book for better techniques and practices for touching up pics, i actuallly learned some new methods )

Photoshop 7 for photographers (excellent manual)

and a Spyder monitor calibrator

[evilenglishman]

yes but dont forget you will get brighter, more vivid colours in RGB than you will in CMYK

[ryuwulf]

yes but dont forget you will get brighter, more vivid colours in RGB than you will in CMYK

yes you are correct. :D

all this reading is making my head hurt!!!!!
ouch!!!!

[Jesper]

Wow, a lot of reactions in such a short time. I know I don't need CMYK for my Epson printer, I was just wondering why evilenglishman was stressing that CMYK is essential in the post about Paint Shop Pro in the EOS Digital forum, because I've never needed CMYK mode and I don't think it's very useful to me. I do use Lab mode in PS CS sometimes to separate the luminosity from the color, if I want to do something with only the luminosity or only the color. Currently there are desktop printers, like the Epson R800, that use even red and blue ink in addition to C, M, Y and black.

[iof]

My printer(the guy that prints my business cards, post cards, flyers, etc., not my inkjet) prefers I send him CMYK. He says:

"Caution: It's Best If You do the RGB-to-CMYK Conversion of Your Images!
You will have more control over the appearance of your printed piece if you convert all of the images from RGB to CMYK before sending them to us. When we receive RGB images, we do a standard-value conversion to CMYK, which may not be perfectly to your liking."

[Point-N-Shoot]

yes but dont forget you will get brighter, more vivid colours in RGB than you will in CMYK

Doesn't that only apply when viewing the photo on a monitor? I thought that you HAD to use CMYK because of the absorbing properties of the photo paper.



The Photoshop tutorial I have statres the following...

Red, Green, and Blue are "additive colors". If we combine red, green and blue light you will get white light. This is the principal behind the T.V. set in your living room and the monitor you are staring at now.

Cyan, Magenta and Yellow are "subtractive colors". If we print cyan, magenta and yellow inks on white paper, they absorb the light shining on the page. Since our eyes receive no reflected light from the paper, we perceive black... in a perfect world!

In practice, printing subtractive inks may contain impurities that prevent them from absorbing light perfectly. They do a pretty good job with light colors, but when we add them all together, they produce a murky brown rather than black. In order to get decent dark colors, black ink is added in increasing proportions, as the color gets darker and darker. This is the "K" or "key" component in Cyan Magenta Yellow and blacK printing.

Additive color, or RGB mode, is optimized for display on computer monitors and peripherals, most notably scanning devices. The printing world operates in subtractive color, or CMYK mode.


So wouldn't that include PHOTO printing??

[Point-N-Shoot]

If all you ever do is make prints at a lab or on a photo printer, you'll only need RGB. <snip>

Well, then that's all I need!!


CMYK images often come in handy for making masks.

For the uneducated (me)...define "masks".


Also, as mentioned, RIP software will let you address your printer heads directly. All these devices are CMYK (with a bunch of extra shades thrown in), so a RIP can improve your printing appreciably by taking the RGB conversion out of the loop.

So, this "RIP" software will improve my images on my photo printer automatically, or just give me more control over the amount of ink used? Most of this stuff is beyond my current level of understanding...I'm still trying to master the manual modes of my DSLR. :confused: