There are always going to be colors we can see in RGB but that we can't achieve in CMYK. Here's the real reason color management is so difficult.

The challenge is that we design on RGB monitors and we print using CMYK devices.

Device - Dependent Color Space

RGB and CMYK are both referred to as device-dependent color spaces because the colors defined in these spaces are intrinsically associated to the devices they are defined on. A device may refer to a printer, scanner, monitor, or any device in which color is created or stored. For example, in a television showroom, each television has a slightly different color even though they are all displaying the same program--they each have their own unique RGB color spaces. Likewise, printers have unique color spaces that vary slightly from printer to printer.

Colors that are defined in device-dependent color spaces cannot accurately be changed to any other device-dependent color space in a direct process because they are not compatible (see images below). Like an interpreter, you need something that can communicate with both RGB and CMYK.

    
 
In the images above, each color space is represented like a piece in a puzzle. Because each piece is unique, they cannot attach to each other. They require another piece. 

Device - Independent Color Space

In 1976, a mathematical color space was created that could be used as an interpreter: LAB. This color space is now the standard method used to interpret between device-dependent color spaces. Because L*a*b* is not dependent on any color space, it is called a device-independent color space.

The L*a*b* color space has three different components:

• L*--This is the lightness value of a color which ranges from 0 (no lightness) to 100 (maximum lightness).
• a*--This value determines the red to green value of a color and ranges from +128 (red) to -128 (green).
• b*--This value determines the yellow to blue value of a color and ranges from +128 (yellow) to -128 (blue).

Because the L*a*b* color space is a consistent standard, any defined value will always be accurate. L*a*b*:65,5,-110 can be correctly understood by an L*a*b* compatible program or device as the exact shade of blue that it was originally designed as. In comparison, you cannot accurately and consistently measure the actual CMYK and RGB color spaces. Because the L*a*b* color space is theoretical, it also has no gamut limitations.

Once an L*a*b* value is defined, accuracy can be guaranteed within the realms of the L*a*b* space even though the source and target of a color are almost always either CMYK or RGB. Because each device-dependent space is different, the idiosyncrasies and gamut restrictions must be taken into account before a translation to the L*a*b* space can occur. This is done with a profile.

In the image above, profiles provide the connecting pieces that join RGB, CMYK, and L*a*b* color spaces together. For more information, see ICC Profiles below.

Profiles can be referred to as ICC Profiles, ICM Profiles, or Color Management Profiles. In ONYX Workflow Products, profiles use either a .icc or .icm file extension. Both formats are supported and used interchangeably.

NOTE: Input Profile define the working space of the source image and can be embedded for a closed color management system and are not the same as Profiles created using Media Manager. Most graphic applications, scanners, cameras and even printers (for proofing) have profiles that can be used as input profiles. Profiles created in Media Manager are considered Output Profile and use a combination of Ink Restrictions, Linearization, Media Model, Ink Limit Table, and so on to create a single file known as a print mode.  These print modes within ONYX contain variables such as: printer technology, ink, media, heat and dryer temps, RIP dot pattern, resolution, ink densities and environment. The profiles/print modes created by ONYX include an ICC Profile component that is built with the ONYX ICC engine/generator.

ICC Profile

An ICC Profile correctly maps a particular device-dependent color space to an L*a*b* standard. A profile also works in a reverse manner to map an L*a*b* value to a device-dependent space. For example, when you scan an image, the original color space of the scanner is RGB. Applying a profile to the image correctly converts the RGB data to an L*a*b* color space. Applying a second profile accurately changes the L*a*b* values to CMYK in order to print the image. If each profile is accurate, the colors of the printed image will match the colors of the original image.

NOTE: It is important to note that profiles are associated to the color space in which they were created. That means that the profiles, too, are device-dependent. Therefore, if you create a profile for one printer, it may not be accurate if you use it with another printer.

You can apply ICC profiles to either convert a device-dependent color space to L*a*b* or to convert L*a*b* to a device-dependent color space; in other words, you can use ICC profiles as either Input or Output Profiles. The only difference between an input and output profile is how you use the profile.

Remember that profiles are device-dependent, and using an input profile as an output profile or vice-versa can cause undesirable color changes in your printed image.

The image above describes the process of converting a color space from RGB to L*a*b* to CMYK to L*a*b* to CMYK. Input profiles convert the device-dependent color space of the image to L*a*b*, and output profiles convert L*a*b* to the device-dependent color space of the output device or file. 

Benefits of Color Management:

• Allows non-specialists to take advantage of specialist's knowledge
• Provides easy communication of color with customers
• Improves overall color consistency
• Makes proofing simple and reliable
• Enables different devices, ink and media to reproduce similar colors
• Reduces print provider's spoilage of consumables
• Reduces everyone's frustration with color
• Helps satisfy the print buyer's color demands

Back to Profiling Fundamentals.

rgb to cmyk.png (image/png)
rgb to lab to cmyk.png (image/png)
rgb to lab to cmyk 1.png (image/png)
cmyk to cmyk.png (image/png)
Lab.jpg (image/jpeg)
Lab.jpg (image/jpeg)
Lab.jpg (image/jpeg)