THE POWER OF DEVICE LINK PROFILES

For many people, the practice of color management is synonymous with using ICC profiles. Profiles describe the specific color space of a device, be it a camera, scanner, or some type of output system like a toner or lithographic printing press. In a traditional ICC workflow, two profiles are required for the complete transformation—an input profile and an output profile, with CIE L*a*b* serving as the color space that connects them, referred to as the Profile Connection Space.

Thinking only of device profiles was understandable because during the developmental years of color management, practitioners were still trying to understand how to apply device profiles, and since early ICC specifications didn’t support device link profiles, creating and using linked profiles was only possible with specialty software.

Times have changed. Last decade the International Color Consortium specifications began to support device link profiles, which expanded the choices of software and RIPs to create and use them. GRACoL and
ISO 12647-2 have also emerged in popularity and device link profiles are ideal to convert content to and from these specifications and standards throughout the myriad of different printing conditions available. Printing companies would be wise to use link profiles in situations when they overcome problems created by traditional device profiles.

What Device Link Profiles Do
Device link profiles convert color directly from one color space to another color space, without the use of an independent profile connection space. It defines the conversion from a source color space to a destination color space by using a look-up table that connects specific input values (e.g., C10 M30 Y20 K10) and corresponding output values (e.g., C9 M28 Y19 K9). In general, the larger the number of “points” in the lookup table, the more accurate the conversion in the link profile. In contrast to device profiles, only one device link profile is needed for the complete transformation.

When to Use Device Link Profiles
By far, the most common use of device link profiles in the printing industry is when it is necessary to repurpose a CMYK file from its original destination color space to a different CMYK destination color space. Examples are when a file is originally separated for a standard condition like GRACoL but must now to be converted to the precise color space of the press that will print the file, or when a CMYK file for the proofer is being converted to the color space for the press. In these instances, using CIE L*a*b* as the connecting space can create undesirable effects such as unsmooth color gradients and converting solid black to a four-color black.

Advantages and Disadvantages
Compared to using traditional profiles, device link profiles have three main advantages when converting from one CMYK space to another:

• Preserving the black channel of the input color space—black text, tints, and solids are maintained as is, thus a 100% black stays 100% black
• Preventing contamination by other colors—the purity of the primary colors (C M Y K) and secondary colors (CM CY and MY) are protected
• Adding some type of ink/colorant optimization that results in ink/colorant savings and better color stability on press

On the other hand, device link profiles are not as flexible as other ICC profiles. A device link profile can only be used for a conversion between two specific device color spaces; a different profile will be needed for each pair of device color spaces. It also can’t be embedded into an image, and only one rendering intent is available—the intent that was selected at the time the link profile was created.

Bottom Line
There are times when device link profiles will result in more reliable color, most notably when converting from one device CMYK color space to another. Newer versions of profiling software can generate such profiles and color RIPs can process them. If your company hasn’t been using them, Printing Industries of America encourages you to take advantage of the power of device link profiles.

What is Device Link Profile?

In a normal workflow situation, the color space of the input device is transformed to the color space of the output device via the device-independent L*a*b* color space (known as the profile connection space). This process requires two different profiles — a source profile and a destination profile. 

Color conversion using source and destination profiles

A device link profile is a special kind of ICC profile that converts the color space of the input device directly into the color space of the output device, whereby the output device can be either a physical printer or a file format. Unlike ordinary source or destination profiles, they do not describe a specific color space, but define the conversion from a source color space to a destination color space. The basis for creating a device link profile is, therefore, always an ordinary ICC profile. 

Device link profiles are most commonly applied to direct CMYK-to-CMYK transformations because converting via a device-independent color space can lead to undesirable effects, such as unsmooth color gradients. In a device link profile the color separations are maintained, thus preserving the black channel of the source profile. 

Color conversion using a device link profile

Indeed, preserving the black channel of the input color space is one of the main advantages of using a device link profile. For this reason, device link profiles are often used during data preparation, e.g. to convert from ISOcoated to ISOuncoated. 

Furthermore, device link profiles enable you to by-pass the L*a*b* color space, thus preventing contamination by other colors, e.g. 50% black stays 50% black. 

However, you should be aware that device link profiles are not as flexible in use as other ICC profiles. Each device link profile can only be used for the specific combination of source and destination profiles for which it was created. 

source: http://www.efi.com/