How Often Should I Reprofile my Inkjet Printer?

Modern inkjet printers generally are very consistent if used and maintained regularly. You should make sure you always use the same type and brand of ink and that the print heads stay free from clogs. Follow these rules for when to profile:

• You will need a separate profile for each combination printer, ink, paper and settings. Even two printers of the same make and model can print differently.
• Re-profile if you upgrade your operating system or change printer drivers.
• If you begin to see a change in your printer's output, double-check your driver settings and test the print heads. If they are all fine, then re-profile.

Several factors contribute to the size of a printer profile:

• The number of channels in the profile.
• The number of nodes in the profiles look-up tables.
• The precision of the data recorded within the profile.
• Additional data stored in the profile tags for reference or future use.

It is the look-up tables (sometimes referred to as a "cube" or "profile cube") that make up the majority of the profile's file size. There are six of these in a typical output profile describing conversion to and from the printer's color space with each of the three rendering intents. Since the CIE-Lab (Lab) color space is used for the device independent profile connection space, there will be three tables describing conversion from Lab to the printer's inks or colorants and three describing conversion from the printer's inks to Lab. You can think of these as the "separation" side and the "what the ink looks like" side of the profile. The ICC shorthand for these are B2A and A2B, respectively.

The amount of detail in many cases the accuracy of the profile is dependent on the number steps for each colorant or channel. By default, current software uses 33 steps per axis on the B2A (Lab to printer) side. That means there are 33 steps for each of the L, a and b axes for a total of 35,937 (33x33x33) combinations. Each of those L, a, & b combinations or "nodes" requires a combination or "recipe" of printer colorant values. For a CMYK profile, there would four numbers in the recipe for each node. The result is a slightly larger amount of data than if it were an RGB profile.

For conversion from the printer space to Lab, the number of colorants has a much greater impact on the profile size. If we use 33 steps per axis for a CMYK profile the A2B (printer to Lab) side will contain 1,185,921 (33x33x33x33) nodes compared to 35,937 for an RGB profile. This exponential increase in nodes is the primary reason profiles typically have fewer steps per axis on the A2B side compared to the B2A side.

The numbers used in those look-up tables can be stored using either 8 or 16-bit precision. With 8-bit precision, there are 256 possible values for each colorant while there are 65,536 for 16-bit. The default is 16-bit and there are few systems that require 8-bit precision. However, a profile using 8-bit precision will be smaller than one using 16-bit

Custom printer profiles typically contain extra data written by the software creating it. In the case of MonacoPROFILER, we include the original patch measurement data and the settings used to create the profile. It is like having a Session file stored within the profile itself. Also, if you edit a printer profile, not only make the change to the profile data, but also store information about what was edited. This is to make the existing edits appear if you attempt to edit or "un-edit" the profile in the future. If you make a lot of edits, this part of the profile will grow accordingly.

If you look at the internals "USWebCoatedSWOP.icc" profile included with Adobe products, you'll find that:

• The Adobe profile contains only 9 steps per axis on the A2B side while Profiler uses 17.
• The A2B0 (perceptual) and A2B2 (saturation) tags point to the same set of data. Profiler creates each A2B tag to be the inverse of the B2A
• The B2A look-up tables use 8-bit precision as opposed to 16-bit precision.
• It contains no vendor specific tags from profile creation software.

The additional detail in the A2B side of the custom profile provides for more accurate soft and hard proofing of the output device. The two A2B tags on the "USWebCoatedSWOP.icc" are 41,478 bytes each while the custom profile contains three unique A2B tags of 558,552 bytes each. The B2A tags in "USWebCoatedSWOP.icc" are 145,588 bytes each while the added precision in the custom profile creates tags of 344,892 each. The vendor specific tags that allow for rebuilding with future releases of Profiler and special editing capabilities add 726,892 bytes to the file size.

While the custom profile is larger, it is needed to provide detail about the unique behavior of a specific device as well as the extra features of the profiling software. A "generic" profile like "USWebCoatedSWOP.icc" is also hand-tuned to be smooth and uniform throughout the gamut, rather than address the behaviors of a particular device. This makes the reduced number of nodes or lower precision less critical than it is with a custom profile. If a small profile is more important than accuracy, or your device's response is colorimetrically very uniform and smooth, then you can reduce the number of nodes and precision in MonacoPROFILER's "Profile Options" page when creating your custom profile.