Why Is Printer RGB When Inks Are CMKY?

AS
Posted By
Alan Smithee
Sep 28, 2005
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607
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14
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I don’t get why "the literature" all says inkjet printers are RGB devices. All the Inks in my printer (Epson R300) are CMYK (CcMmYK). Wouldn’t it make more sense to send CMYK info to the printer? Can I do this? Can someone explain the history behind this decision? Thx.

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E
edjh
Sep 28, 2005
Alan Smithee wrote:
I don’t get why "the literature" all says inkjet printers are RGB devices. All the Inks in my printer (Epson R300) are CMYK (CcMmYK). Wouldn’t it make more sense to send CMYK info to the printer? Can I do this? Can someone explain the history behind this decision? Thx.
Interesting question.

Think about it. You CAN’T print in RGB. Inkjet printers make the conversion from RGB to CMYK for you. I don’t know the history but I surmise that the majority of computer users don’t have software that can handle CMYK files, and I believe in the early days only Macs could handle CMYK at all.

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T
Tacit
Sep 28, 2005
In article <xon_e.566990$>,
"Alan Smithee" wrote:

I don’t get why "the literature" all says inkjet printers are RGB devices. All the Inks in my printer (Epson R300) are CMYK (CcMmYK). Wouldn’t it make more sense to send CMYK info to the printer? Can I do this? Can someone explain the history behind this decision? Thx.

They made this decision in part because the CMYK used by the printers is not the same as the CMYK used by a printing press or by a program like Photoshop.

Inkjet printers are CMYK, but not SWOP CMYK. In particular, the "cyan" ink in an inkjet printer is not pure cyan; it’s more blue. Inkjet printers do this because the manufacturers know that consumers like more vivid colors, and by using a cyan ink that’s biased toward blue, the color is more pleasing to consumer users.

A CMYK image is not useful to an inkjet printer because if you take a CMYK image and print it using the inkjet printer CMYK inks, the image will not match what you see on the screen, because the inks don’t match.

Also, printers that use CMmYyK would still need to be re-separated anyway; CMYK does not map directly onto the printer’s CMmYyK inks.

The inkjet printer driver software acccepts data in RGB, then separates it to the printer’s own peculiar brand of CMYK or CMmYyK. If you send an inkjet printer a CMYK image, the result is usually pretty awful, because the driver software converts it (badly) to RGB, then back to the printer’s own color space.


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BH
Bill Hilton
Sep 28, 2005
Alan Smithee writes …

I don’t get why "the literature" all says inkjet printers are RGB devices.

That’s easy … because the inkjets want an RGB input file and then do the conversion internally.

All the Inks in my printer (Epson R300) are CMYK (CcMmYK). Wouldn’t it make more sense to send CMYK info to the printer?

It would make no sense at all to send it CMYK since your printer wants CcMmYK … you’re tossing away light cyan and light magenta right off the bat. Start to see the problem? Then there are the seven and eight color printers that would toss away even more …

Wouldn’t it make more sense to send CMYK info to the printer? Can I do this?

Sure you can do it and then the printer driver will translate back to RGB and then back again to CcMmYK … great way to screw things up.

Bill
J
John
Sep 28, 2005
"Alan Smithee" wrote in message
I don’t get why "the literature" all says inkjet printers are RGB devices. All the Inks in my printer (Epson R300) are CMYK (CcMmYK). Wouldn’t it
make
more sense to send CMYK info to the printer? Can I do this? Can someone explain the history behind this decision? Thx.

You have to remember that inkjet printers have evolved from simple desktop printers, designed to be simple and straightforward. Computer applications, with the exception of the dedicated desktop publishing and imaging programs that we all now take for granted, are primarily interested in producing output for the screen, i.e. RGB. Printing, as far as these less sophisticated apps are concerned, is simply an extension of viewing on the monitor, so the simplest solution is to dump the RGB to the printer and let the printer driver worry about it. That way, each individual application doesn’t have to have built into it a sophisticated printer driver to convert from RGB to CMYK.

As other posters in this thread have indicated, CMYK conversions are not for the faint hearted and each type of printer has its own requirements in terms of (e.g.) black generation, total ink limits and colour rendering. It makes sense for the printer driver to cope with this. However, as all of us know, this approach can and does cause limitations.

It is possible to print CMYK to inkjets, but to do so, you need to purchase a dedicated Raster Image Processor (RIP) and print from this rather than the normal printer driver. This can be software only (e.g. Epson’s own Stylus RIP software) or a combination of hardware and software (as in a EFI colour server). These devices accept Postscript data, which can be CMYK, RGB or a combination of both.


John
Replace ‘nospam’ with ‘todnet’ when replying.
N
nomail
Sep 28, 2005
Alan Smithee wrote:

I don’t get why "the literature" all says inkjet printers are RGB devices. All the Inks in my printer (Epson R300) are CMYK (CcMmYK). Wouldn’t it make more sense to send CMYK info to the printer? Can I do this? Can someone explain the history behind this decision?

Read the literature again. It doesn’t say that an inkjet printer is a ‘RGB device’, it says that an inkjet printer needs ‘RGB input’. That is not the same!

The reason is simple. All your programs can handle RGB data, but very few can handle CMYK data or can convert RGB data to CMYK. If your home inkjet printer needed CMYK data, most of your programs would not be able to print to it. That’s why the manufacturer decided along time ago to write a printer driver that handles the conversion from RGB to CMYK. Later this became even more important when new kinds of inkjet printers were developed with more inks, like the six, seven or eight color inkjet printers of today.


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MR
Mike Russell
Sep 28, 2005
Alan Smithee writes …

I don’t get why "the literature" all says inkjet printers are RGB devices.

There are several answers to this question, and my take on it is somewhat different from Bill’s or Tacit’s. For one, I see no quality issue with printing a CMYK image on an inkjet. The extra trip to RGB space is not a significant problem, IMHO.

The main reason that printers are RGB devices is that this is the interface provided by the operating system, Mac, Windows, SUN, and others. Therefore all printer manufacturers provide RGB drivers for their devices.

For inkjets, the RGB driver converts the RGB values to the actual dots of ink that go on the page, and part of this conversion is translating RGB to CMY, CMYK, or CcMmYK.

When you print a CMYK image from Photoshop, here’s what happens.

1) the image is converted from CMYK to RGB (in photoshop, not the driver) using the specifications you provided in your Printer Setup aka Print Preview.

2) the driver converts the RGB data to dots.

But there’s way to look at your question. CMYK is really RGB in disguise. Inks work by absobing part of light reflected from the paper. Cyan absorbs red, magenta absorbs green, and yellow absorbs blue. So red will print as a mixture of magenta and yellow, and other colors are translated in a similar way

Also, there are ways to print directly in CMYK, using postscript.

If you want to experiment with using CMYK in Photoshop, go ahead. You’ll see some reduced saturation in certain blue colors, but for most images this is not a big deal, and there are ways to deal with this. —
Mike Russell
www.curvemeister.com
BH
Bill Hilton
Sep 28, 2005
Mike Russell writes …

I see no quality issue with printing a CMYK image on an inkjet. The extra trip to RGB space is not a significant problem, IMHO.

I *think* you are talking about editing in CMYK, converting to RGB and sending to the inkjet while Alan is asking why he can’t send a CMYK file directly to the printer without converting … but maybe I misunderstood one or both of you.
MR
Mike Russell
Sep 28, 2005
"Bill Hilton" wrote in message
Mike Russell writes …

I see no quality issue with printing a CMYK image on an inkjet. The extra trip to RGB space is not a significant problem, IMHO.

I *think* you are talking about editing in CMYK, converting to RGB and sending to the inkjet while Alan is asking why he can’t send a CMYK file directly to the printer without converting … but maybe I misunderstood one or both of you.

No, you’re correct about the original post. Two of the responses, including yours, warned specifically against printing a CMYK image, as if it were a bad practice, and I was responding to those.

In fact, there are substantial advantages to editing in CMYK, including better control of shadow detail, and the ability to use curves for more subtle color adjustments. There are also ways to minimize the loss of blue saturation, for those images that are affected.


Mike Russell
www.curvemeister.com
AS
Alan Smithee
Sep 28, 2005
Mike Russell wrote:
"Bill Hilton" wrote in message
Mike Russell writes …

I see no quality issue with printing a CMYK image on an inkjet. The extra trip to RGB space is not a significant problem, IMHO.

I *think* you are talking about editing in CMYK, converting to RGB and sending to the inkjet while Alan is asking why he can’t send a CMYK file directly to the printer without converting … but maybe I misunderstood one or both of you.

No, you’re correct about the original post. Two of the responses, including yours, warned specifically against printing a CMYK image, as if it were a bad practice, and I was responding to those.
In fact, there are substantial advantages to editing in CMYK, including better control of shadow detail, and the ability to use curves for more subtle color adjustments. There are also ways to minimize the loss of blue saturation, for those images that are affected.

I think I was pondering my navel a bit…I was thinking since the final output is based the CMKY (subtractive) ink it would make the most sense to stay in that model upstream. My understanding of the CMYK system is from working on the editorial side of print. Basically I was told (back in the day) that the black is there — because it’s already on the presses and we use it a lot — and the model evolved from that point. Something to do with RGB inking being too wet to make black on the newspaper print and it would be more costly. Thanks for the tip about CMYK editing Mike. I’ve just downloaded the Wide Gamut CMYK colour space file, I don’t it it’s going to do much to help my "workflow" issues, but it’s interesting to see the way you can play with the K channel similar to Lab.
I
iehsmith
Sep 29, 2005
On 9/28/05 4:25 PM, Alan Smithee uttered:

Mike Russell wrote:
"Bill Hilton" wrote in message
Mike Russell writes …

I see no quality issue with printing a CMYK image on an inkjet. The extra trip to RGB space is not a significant problem, IMHO.

I *think* you are talking about editing in CMYK, converting to RGB and sending to the inkjet while Alan is asking why he can’t send a CMYK file directly to the printer without converting … but maybe I misunderstood one or both of you.

No, you’re correct about the original post. Two of the responses, including yours, warned specifically against printing a CMYK image, as if it were a bad practice, and I was responding to those.
In fact, there are substantial advantages to editing in CMYK, including better control of shadow detail, and the ability to use curves for more subtle color adjustments. There are also ways to minimize the loss of blue saturation, for those images that are affected.

I think I was pondering my navel a bit…I was thinking since the final output is based the CMKY (subtractive) ink it would make the most sense to stay in that model upstream. My understanding of the CMYK system is from working on the editorial side of print. Basically I was told (back in the day) that the black is there — because it’s already on the presses and we use it a lot — and the model evolved from that point. Something to do with RGB inking being too wet to make black on the newspaper print and it would be more costly. Thanks for the tip about CMYK editing Mike. I’ve just downloaded the Wide Gamut CMYK colour space file, I don’t it it’s going to do much to help my "workflow" issues, but it’s interesting to see the way you can play with the K channel similar to Lab.

My inkjet is an ancient Epson 900 and my prints aren’t color critical in the least. I don’t exactly convert to RGB. Most of what I need printed are Quark documents with photos or other imported images like Illustrator EPS. Not having RIP software for my printer, I create a PDF (colors unchanged) from my Quark doc and print from that. My colors are ‘generally’ close enough.

With the exception of printing RGB photos from Photoshop; I’ve gotten worse results when converting to RGB, like allowing Distiller (4) to convert my CMYK Quark docs to RGB or making Quark print an RGB composite to PS file for distilling to PDF.

inez
T
Tacit
Sep 29, 2005
In article <vuD_e.3335$>,
"Mike Russell" wrote:

No, you’re correct about the original post. Two of the responses, including yours, warned specifically against printing a CMYK image, as if it were a bad practice, and I was responding to those.

And the advice stands.

Photoshop is a smart graphics application; if you print a CMYK image, Photoshop converts the CMYK data to RGB data. The driver never "sees" the CMYK and believes the image is RGB.

Other, non-Photoshop applications may not do this, or may do it very poorly. Therefore, as a generic case, images should not be sent to an inkjet printer in CMYK save for from Photoshop,l which is more sophisticated than any other programs out there when it comes to providing the printer driver with decent RGB from a CMYK image. If you print CMYK to an inkjet printer from a less capable image editing program, for example, or from a consumer-grade desktop publishing program or the like, you’ll get garbage.


Art, photography, shareware, polyamory, literature, kink: all at http://www.xeromag.com/franklin.html
GH
Gernot Hoffmann
Sep 29, 2005
Tacit,

I can print CMYK images by PhS to a PostScript printer
WITHOUT going through RGB.

Just choose in Print with Preview: As Source.

Good so, because calibration targets for PostScript
printers are defined by CMYK numbers, and any conversion would confuse the calibration.

Of course: a PostScript printer is NEVER a so-called
RGB-printer.

Best regards –Gernot Hoffmann
T
Tacit
Sep 30, 2005
In article ,
wrote:

I can print CMYK images by PhS to a PostScript printer
WITHOUT going through RGB.

Typical consumer inkjet printers aren’t PostScript. PostScript changes everything; an inkjet printer with a PostScript RIP accepts CMYK just fine.


Art, photography, shareware, polyamory, literature, kink: all at http://www.xeromag.com/franklin.html
J
JJSrock
Oct 4, 2005
Alan Smithee wrote:
Mike Russell wrote:
"Bill Hilton" wrote in message
Mike Russell writes …

I see no quality issue with printing a CMYK image on an inkjet. The extra trip to RGB space is not a significant problem, IMHO.

I *think* you are talking about editing in CMYK, converting to RGB and sending to the inkjet while Alan is asking why he can’t send a CMYK file directly to the printer without converting … but maybe I misunderstood one or both of you.

No, you’re correct about the original post. Two of the responses, including yours, warned specifically against printing a CMYK image, as if it were a bad practice, and I was responding to those.
In fact, there are substantial advantages to editing in CMYK, including better control of shadow detail, and the ability to use curves for more subtle color adjustments. There are also ways to minimize the loss of blue saturation, for those images that are affected.

I think I was pondering my navel a bit…I was thinking since the final output is based the CMKY (subtractive) ink it would make the most sense to stay in that model upstream. My understanding of the CMYK system is from working on the editorial side of print. Basically I was told (back in the day) that the black is there — because it’s already on the presses and we use it a lot — and the model evolved from that point. Something to do with RGB inking being too wet to make black on the newspaper print and it would be more costly. Thanks for the tip about CMYK editing Mike. I’ve just downloaded the Wide Gamut CMYK colour space file, I don’t it it’s going to do much to help my "workflow" issues, but it’s interesting to see the way you can play with the K channel similar to Lab.

CMYK values in PS (or any other image editor) do not map exactly or directly into CMYK ink values in a printer. For instance, CMYK of a color is represented by four values in an editor, but many printers have more than four CMYK ink colors.

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