Online Printing: RGB vs CMYK

Introduction

There is alot of confusion and misleading information about RGB and CMYK color spectrum amoung the printing industry, specially by small and medium sized companies who depends of 3rd party service to print the actual product.

In this section we will try to break some taboos and provide you all the context necessary to understand how the color structure works and the difference between web and printing.

RGB Palette (Red, Green and Blue)

The Internet, as we know, uses RGB colors. RGB colors have a huge range of colors, IE.: RGB 24 bits is equal to 256X256X256 = 16.777.216 color combinations. The RGB colorspace is perfect to display content with live color and contrast.

CMYK Colorspace : Cyan, Magenta, Yellow and Black

The CMYK color model (process color, four color) is a subtractive color model, used in color printing, and is also used to describe the printing process itself.

CMYK refers to the four inks used in some color printing: cyan, magenta,yellow, and key (black).

Though it varies by print house, press operator, press manufacturer and press run, ink is typically applied in the order of the abbreviation.

The "K" in CMYK stands for key since in four-color printing cyan, magenta, and yellow printing plates are carefully keyed or aligned with the key of the black key plate. Some sources suggest that the "K" in CMYK comes from the last letter in "black" and was chosen because B already means blue. However, this explanation, though plausible and useful as a mnemonic, is incorrect.

The CMYK model works by partially or entirely masking colors on a lighter, usually white, background. The ink reduces the light that would otherwise be reflected. Such a model is called subtractive because inks "subtract" brightness from white.

In additive color models such as RGB, white is the "additive" combination of all primary colored lights, while black is the absence of light. In the CMYK model, it is the opposite: white is the natural color of the paper or other background, while black results from a full combination of colored inks. To save money on ink, and to produce deeper black tones, unsaturated and dark colors are produced by using black ink instead of the combination of cyan, magenta and yellow.

RGB vs. CMYK : Pratical Use on the Web

As mentioned above, the Internet (and your computer OS) is based on RGB colorspace. It is impossible to display CMYK on monitors, regardless or mark or quality.

From this point, the following problems emerges:

1. Color difference while designing or editing products in any software (PC, Mac or Internet based Apps)

2. Screen configuration (99% or all users uses manufacture's default confuguration)

3. CMYK profile embed on PDF

See below some of the most common problems arising due colorspace and screen problems.

Case Study: PDF or JPG provided by the client

Assuming that the media provided is a PDF or JPG with CMYK profile embed deisgned by a professional with calibrated monitor, let us analyse the following situation.

- A customer orders a flyer design which will be sent to printing. After designing the flyer, the artwork is sent to the customer for review.

The customer opens his email on his machine (PC) and replies to the graphic designer that the logo should have a stronger blue color to match his company's flag. After performing the necessary changes, the customer finally approves the work which is sent for print job.

After a couple of day, the customer calls the graphic designer complaining that the blue is different from what he saw (in his machine) and it doesn't match his company's color.

Problem sources:

a. The graphic designer failed to assume that the client will not have calibrated monitor or knowledge of colorspace.

b. The graphic designer failed to inform the client about colorspace differences (RGB/CMYK)

c. The customer failed in reviewing the job in a non-calibrated monitor

Solution

- There is no solution. Printable products will always have the CMYK curse, regardless of color profile.

Experiment: Printing PDF or JPG without and with CMYK Profile

(This experiment requires a calibrated monitor)

- On your favorite graphic editor, draw 3 squares, one blue (255), one green (255) and one red (255) which represents the basic RGB colors.

Save the document in PDF or JPG and send it to print (home/office printer).

- Now, convert the same document to CMKY colorspace. Print it out using your home printer (same printer for both documents).

Notice the colors on the two sheets. They should have noticeable differences in colors. Now, let us analyse what just happened.

When you add certain RGB colors into a document such as pure blue or green, you are defining the color to 255 on it's channel and 0 to the other two channels. That's fine even if you want to print that. The problem occurred when you converted the document to CMYK. Because CMYK works by mixing 4 colors making the color palette really short comparing to RGB, it will be very likely that the profile instructions changes the blue to a color close to purple.

Why? - because there is no formula or mathematic meanings to conver RGB to CMKY with accuracy.

Conclusing

All printers print in CMYK. The proof of that is that, even your printer has 4 to 6 colors on it's color deck.

So, why RGB are printed with accuracy while CMYK profile mess it up?

The answer is simple. The convertion performed by the printer is better than the graphic application.

To prove this concept, we used EcommDS output data (pdf) and sent the same document to print in two formats:

- With CMYK profile embed (added using Adobe inDesign CS5.5)

-  EcommDS PDF output as is, without any modification.

Printing companies used:

- FlyerAlarm (http://flyeralarm.de)

- VistaPrint (http://www.vistaprint.de)

Documents printed

2x Business Card 91x61mm 4/4 356dpi 2 sides 300g (CMKY + RGB)

2x Post Card DINA6 Quer 105X148mm 4/4 356dpi 2 sides  UV lack 300g (CMKY + RGB)

2x Flyer DINA6 Quer 148X105mm 4/4 300dpi 2 sides 135g (CMKY + RGB)

The results were outstanding.

CMKY: suffered some color changes in which affected mostly the blue color but matches the CMYK PDF converted on inDesign.

RGB: surprisingly, the PDF without profile matches the JPG output* and also the PDF which corresponds to what we designed using  EcommDS. Undoubltly, the professional printer has better conversion methods than Adobe colorspace conversion.

* Because  EcommDS outputs a PDF plus high quality JPGs as output, we were able to compare the results.

Compare

 The image below will display different colors depending on your monitor's settings:

Our conclusion

IMPORTANT: We are, in no way, trying to impose our conclusions to you. If you are interested, you should perform the experiment yourself.

When it comes down to providing printing products in which a user is allowed to interact with the product, we found that CMYK profile actually "gets in the way and caused us more trouble that solution".

CMYK Profile is great when used by graphic professionals and also allows on the view the exact print output (of course, with a calibrated monitor) but in the web, that just gets in the way.

We will always assume that the client is unfamiliar with printing process and has no clue of what CMYK is.

We also concluded that there is no solution for screen visualization regardless of settings. There is no standard when it comes down to color fidelity. There will be always the risk of customers complaining about how different the print looks from the digital media.

The only solution we could think of is to provide a strong documentation and required check boxes where users must read and agree that the actual print may differ from digital screen image.