K20: A Rationale for CMYK…

rbst_k20_2x2_y

When using Adobe Photoshop (PS), what color space do you work in…?

The two things I hear all the time are:

  1. Work in RGB. You can choose more colors. They’ll pop more. And, you’ll have access to more filters.
  2. Work in CMYK. If you start in RGB, you’ll have to convert to CMYK before you print anyway.

rbst_book_sbx

My final goal with most of my work is print, so this explanation is geared to that end. The following charts were created using PS Creative Suite (CS)  5.1 and InDesign (ID) CS 5.5; then exported as RGB *.jpg’s for web posting. 


I choose to work in CMYK because I can control the color better.


1. We use K20 as part of a 20% CMYK test pattern at the shop. It’s a neutral color that gives us a good starting point for the following conversion exercise.

These charts illustrate (left to right) a 72 dpi grayscale square filled with 20% black (K20)1 and it’s behavior through color conversion followed by one pass of PS’s color halftone filter (Filter > Pixelate > Color Halftone) using default settings.


ss_photoshop_filter_halftone_default2. PS Color Halftone Dialog: Default settings.
rbst_k20_chart_x2

K20 (RGB) produces a vibrant halftone after filter. But, converting to CMYK desaturates the pattern.

rbst_k20_chart_x

K20 (CMYK) produces a less vibrant halftone after filter. The dots are smaller and don’t suffer desaturation after conversion to RGB. What you see is what you get (WYSIWYG).

What do those charts have to do with anything…?

I thought it might be a simple way to show what happens during color conversion.

Suppose you’re creating a graphic that’s to be printed and used on the web. Based (loosely) on the charts above, starting off with an RGB document has potential for a more vibrant onscreen image. That’s because RGB has a larger colorspace than CMYK, so you get a wider range of visible color. But, since a large portion of the RGB colorspace falls out of CMYK gamut, you risk losing a lot of that saturation when converting for print.

Starting with a CMYK document does limit your color palette. But, it’s colorspace is smaller than, and falls within, the RGB gamut, so converting for onscreen display doesn’t really change what you see, for the most part.

What does that all mean…?

Basically, If I’m drawing something with intent to print, I don’t want my colors getting dulled out beforehand.

What’s the final breakdown…?

When I draw or design something, I start in CMYK so that what I print out will more closely resemble what I’m looking at onscreen. I just want to avoid an unexpected color shift.


CMYK Pros

  • More accurate color for print.
  • Conversion to RGB is less likely to result in color shift.

CMYK Cons

  • Less color choices than RGB.
  • Reduced PS filter options.

RGB Pros

  • More color choices than CMYK.
  • More filter options.

RGB Cons

  • Higher chance of color shift when converting to CMYK.
  • Less accurate color for print.

Can you see my source files…?

RBST K20 Source Files

ss_rbst_k20_source_x

For this one, sure. Download them with the link on the left. I conducted this exercise on OSX, so the color labeling doesn’t apply if you’re looking at the files on Windows.

RBST_K20/..
Green files are the ID files used to export the web images used in this post.

../_FONTS
Typefaces used in the ID files.

../_JPG
Green files are layer exports out of the gray files in /_PSD.
Red files are byproducts of the layer exports.

../_PSD
Gray files are the native files that I began with, complete with named layers.

../_WEB
Purple files are the images used in this post, exported out of ID.


I’m open to hear opinions or ideas.

What do we know about the subject at-a-glance? And, how can we expand on that knowledge…?

Comments are welcome…

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2 comments
  1. I say submit RGB, embedded with an ICC profile like Adobe RGB. This way a prepress department can convert to device dependent CMYK, this is especially important if the printer has multiple print technologies.This workflow is called “Late Binding” If the shop is a one press shop where the CMYK is somewhat static and predictable in terms of density tolerances, then converting to the prefered CMYK is beneficial [ Web Offset or SWOP or Sheetfed Coated or Uncoated ], For instance, a Web Offset Press such as a Magazine printer. Or even a commercial shop that has a sheetfed press. But a digital shop may have multiple print technologies and it’s best if the conversion from RGB to CMYK happen once, not twice. Because if you submit CMYK say converted in PS, the default CMYK is US Web Coated SWOP v2 based on a web press, it’s total ink limit and color gamut is limited and constrained to fit the tolerances of a Web Offset Press. Then that constrained CMYK will be converted again to the digital press [ i.e Indigo 5500 ] CMYK profile which most likely yields a larger color gamut. Double conversion increases the chances for colors to shift and change. It’s best to let the RIP convert once from RGB to CMYK if the RIP can handle it. It really all depends on the RIP and it all depends on the printer.

    • RBST said:

      Marc:

      Thanks for chiming in. Those are really good points.

      My main point in starting with CMYK is to begin with a reduced parameter that doesn’t set me up for disappointment when printing. It’s along the same lines as when designers choose multiple PMS colors but intend to print CMYK. So many of those colors are not possible at the 4-color print stage.

      So, my question is, if you do start with Adobe RGB as your profile, how much of that will actually fall into the CMYK gamut at print? Converting to device independent still reduces whatever is out of that gamut.

      I think the way to monitor what you’re going to get while working (PS) in RGB is to work with a Working CMYK Proof Setup*. A calibrated monitor might be necessary for that, though.

      * PS : View > Proof Setup > Working CMYK

      What do you suggest…?

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