RGB-CMYK

[mdaddyrabbit]

Some one explain to me what is meant when you use RGB and CMYK in abobe PSCS. I have the epson 2200. I am not clear on this?

[slin100]

I wouldn't worry about CMYK. The consumer-level Epsons expect image data in RGB. CMYK is generally reserved for prepress processing, although I have read about some advanced color correction techniques using CMYK.

[Scottes]

Yup, don't worry about CMYK until you need to send 4-color seperations to a print press. And by then you'll *know* you need to worry about CMYK! :-)

[BDM]

I also understand that the dynamic range and color gaumet are not as wide in CMYK as in RGB so we are fortunate that our inkjet and photographic based printers use the RBB colorspace.

Bruce

[Jesper]

Some more background info: Computers can represent colours in different ways. The most common way is to represent a colour using a combination of the three components red, green and blue (RGB). By mixing red, green and blue light in different amounts, you can produce lots of different colours.

Printers and printing presses usually use different colours than red, green and blue for making colours, such as CMYK (Cyan, Magenta, Yellow, blacK). Modern ink jet printers have even more inks, for example the Epson R800 and R1800 use cyan, magenta, yellow, red, blue and two types of black ink.

I have no experience with this myself, but if you prepare an image for a printing press that uses CMYK inks, you can work in CMYK mode in Photoshop and you'll have more control over how the image is going to look when it is printed by the press.

If you're not preparing images for a printing press, there's no advantage in working in CMYK mode in Photoshop. Inkjet printers such as your Epson 2200 expect images to be in RGB format and the printer driver or maybe even the printer itself will calculate which mix of inks it needs to use from the RGB data. If you'd convert your image to CMYK in Photoshop and print it, Photoshop will convert it back to RGB under the covers before it sends the image to the printer driver.

[UncleDoug]

Some more background info: Computers can represent colours in different ways. The most common way is to represent a colour using a combination of the three components red, green and blue (RGB). By mixing red, green and blue light in different amounts, you can produce lots of different colours.

Printers and printing presses usually use different colours than red, green and blue for making colours, such as CMYK (Cyan, Magenta, Yellow, blacK). Modern ink jet printers have even more inks, for example the Epson R800 and R1800 use cyan, magenta, yellow, red, blue and two types of black ink.

I have no experience with this myself, but if you prepare an image for a printing press that uses CMYK inks, you can work in CMYK mode in Photoshop and you'll have more control over how the image is going to look when it is printed by the press.

If you're not preparing images for a printing press, there's no advantage in working in CMYK mode in Photoshop. Inkjet printers such as your Epson 2200 expect images to be in RGB format and the printer driver or maybe even the printer itself will calculate which mix of inks it needs to use from the RGB data. If you'd convert your image to CMYK in Photoshop and print it, Photoshop will convert it back to RGB under the covers before it sends the image to the printer driver.


This brings up some interesting topics.

You can convert to the printer profile/space, by-pass color management at the RIP and it will print fine.
Now comes the question, is my printer profiled as a 4-color(cmyk), a 3-color(rgb) or a multi-chanel device(n-color).

PS does not natively support n-color spaces as of now.
I believe Pantone has and either(maybe both, can't remember)Gretag-Macbeth or Monaco a plug-in that allows one to work with images in n-color spaces.
This is completely out of hand and should be avoided unless you like severe self-inflicted mental torture.

So we are left with 3 or 4 color as the possibilities.
Traditionally ink jets were profiled as 4-color devices.
Now days many are profiled as 3-color(rgb) devices. Just the way dye-sublimation printers and light-jets are.
This is to leverage the extra colors and scales of black without having to use proprietary code in the profile and a dedicated RIP to work with the profiles.
Our Roland FJ-500 came with profiles from the factory that are cmyk+"secret sauce".
The "secret sauce", extra proprietary code in the profile, helped to leverage the orange, green, Lcyan, Lmagenta - in effect broadening the color space - in the RIP provided.

If you have time, media and ink to burn, ha-ha, play with it a bit.
You will learn a great deal.

[Scottes]

Heck, it used to be a lot easier in the simple days of RGB->CYMK conversion, when all you had to worry about was undercolor removal algorithms to get the black base computed. Then Grey Component Replacement made prints better at the cost of more brain cells. Now we have Cyan CR, LCyan CR, Magenta CR....

Argh. My brain hurts!

[Jesper]

This brings up some interesting topics.

You can convert to the printer profile/space, by-pass color management at the RIP and it will print fine.You can convert your image to the colour space of the printer using Image / Mode / Convert to Profile in Photoshop, but the image will still be an RGB image. Photoshop just converts the RGB numbers so that if you send these RGB numbers to the printer directly (bypassing any corrections done in the printer driver), the print will look right. The driver (or printer itself) still needs to convert the RGB numbers to combinations of ink droplets.

PS does not natively support n-color spaces as of now.Well, Photoshop CS does support multichannel images (see Image / Mode / Multichannel), but I have no idea what that is useful for...

[UncleDoug]

You can convert your image to the colour space of the printer using Image / Mode / Convert to Profile in Photoshop, but the image will still be an RGB image. Photoshop just converts the RGB numbers so that if you send these RGB numbers to the printer directly (bypassing any corrections done in the printer driver), the print will look right. The driver (or printer itself) still needs to convert the RGB numbers to combinations of ink droplets.

Well, Photoshop CS does support multichannel images (see Image / Mode / Multichannel), but I have no idea what that is useful for...


Jesper,

Your image will still be an RGB image if and only if the profile you are converting to is an RGB profile. If the profile you are converting to is a CMYK profile your image will the become a CMYK image.
Try it in PS.
Open an image that is in an RGB space, sRGB, Adobe, what ever.
Then convert it to SWOPCoated.
The header in the upper frame of your image will reflect the change, also look at your channels tab....

When you print an RGB image via a RIP with color management, several things happen.
First the RGB numbers are converted to LAB and then from LAB to the printer space(be it CMYK, RGB, or N-Color).
LAB is the "DMZ" of color - all things are equal here, about as close as you can come to a uniform perceptual color space.
Then the RIP takes this information and, depending upon your RIP the ink cart configuration, breaks things down even further to address the individual channels of your printer to squirt out ink. if you were to profile your printer as an N-Color device it would have as many channels as your printer has ink carts.
So if you convert to your output space before sending to the RIP you are performing the task of color management in the RIP.
When you send an image to the RIP this way you want color management off, otherwise the RIP will do this......
PrinterSpace-to-RIP RGB(user defined in RIP color management)-to-LAB-to-PrinterSpace.
All sorts of unnecessary conversion and image color degredation.

The multi-channel feature in PS. I believe, is geared at the prepress world for working with bump plates and the like.
As of PSCS1 there is no native support for images that use a n-color profile.
I have a profile for Hexachrome on our Roland that is a true N-Color profile, representing all 6 channels of Hexachrome.
Photoshop will see the profile, but it will not let me assign or convert to it, because it is an N-Color profile.

[UncleDoug]

For those interested......If you want to see comparisons of various RGB working spaces that follows an excellent scientific method, check this site.

BruceLindboom.com (http://www.brucelindbloom.com/)

1. Click INFO...

2. Then click
Information About RGB Working Spaces

It is a bit heady, but does provide interesting comparisons of the major spaces out there.