Output Color Management
Introduction
The Ergosoft RIP provides several tools for color management. These tools can be separated into two distinct parts of the color management workflow: tools that affect input colors and tools for output control.
Input Color Management mainly deals with settings affecting the colors of the image itself, such as the conversion of the image from the original color space to the internal LAB color space of the ErgoSoft RIP. It covers settings regarding input profiles and rules for color conversion.
The rendering intent is part of the input color management and specifies how out-of-gamut colors of the device-independent Lab color space are to be converted into the printer gamut. This conversion is necessary because the Lab color space holds much more colors than the printer gamut.
More direct ways of controlling the colors such as modifying the color in the image or parts of the image also fall into this category.
Output Color Management deals with the density linearization, ink limitation, and output profile (printer profile). The tools and features that combine to transition the image from the ErgoSoft RIPs internal LAB color space to the output color space.
Output Color Management
Output color management regulates the transition from the softwares internal LAB color space to the color space of the printer. Since it controls how the colors will come out of the printer, it handles 3 distinct tasks:
- Linear Ink Coverage: The ink amount used should rise continuously from 0% (no ink) to 100% (all ink) without gaps, steps, and cracks.
- Ink Amount Control: To regulate the amount of ink applied to the medium. Enough the ensure coverage, but not too much so as to avoid effects like bleeding, flaking, etc.
- Color Mixtures: Controlling the color recipes to account for the individual tints of the inks that are used as well as the material that is used, as both can have a large impact on the final perception of colors in the final printout.
To achieve these goals, basic output color management consists of three parts: The density linearization, the total ink limit and the printer profile. All Three of these are set in the Print Environment dialog in the Quality tab. You can access it by selecting the Print Environment you would like to view the settings for, clicking on the Settings button and then the Quality tab.
The dropdown menus show the selected Density Linearization and Printer Profile. The Total Ink Limit is set by checking the box "Apply Total Ink Limit" and defining the percentage value in the bottom field labeled.
Density Linearization
The density linearization registers information about the amount of ink that is applied to the material when printing. Due to mechanical and practical components such as ink drop size defined by printer technology, absorption rate of the material, etc. each printing setup can vary wildly in how much ink is applied and how it behaves. The ink drop size of one printer might be just large enough so 100% ink application can be used on a material, but the drop size of another printer might be too large and cause bleeding. The perfect amount of ink on one material might be way too much for another.
The density linearisation charts the behavior of the machine, ink and material on a linear scale and registers how all the components behave on a scale from 0% to 100% application using measurements from a spectrophotometer. It then applies a correction factor to ensure that the coverave at any point on the 0 to 100 gradient matches the expected coverage.
Ink Application is a very variable part of the printing process, as it can be affected by machine age, print head maintenance, and even vary between different cartridges of the same ink. It is therefore advisable to repeat the density linearization procedure from time to time to ensure it is still accurate. This is generally called a re-linearization where an existing linearization is re-measured to ensure it has up to date values.
Total Ink Limit
While density linearisation controls the ink amount of a single, specific color channel or ink to be applied, the total ink limit deals with the maximum amount of ink that can be applied by mixed colors i.e. ink mixtures. Total Ink Limit is set as a separate parameter from the density linearization and controls how much ink in percent a mixture may apply at maximum.
For example, a Total Ink Limit Value of 400% would allow 100% of each Cyan, Magenta, Yellow and Black to be applied, which is too much for most materials and would cause undesired effects such as pooling of inks. A limit of e.g. 260% on the other hand would allow mixtures linke 100% Cyan, 100% Magenta, 50% Yellow and 10% Black or any other combination that does not exceeed a total of 260% application.
To determine the Total Ink Limit , ErgoSoft RIPs provide a handy chart that shows different ink mixtures with increasing values, allowing you to easily assess the maximum amount of ink that still produces good results.
Printer Profile
The printer profiles contain specifications about the required mixture of the process colors to create colors. It does this by measuring charts of mixed colors and registering how different color mixtures look given the particular ink/media/printer combination. It then uses the measured values to apply corrections to the output colors, ensuring that colors look like they are expected to.
For example one ink/media/printer combination might have an emphasis on bluish tones if colors like Cyan are more dominant. The color profile will register that combinations containing Cyan drift towards blue and attempt to adjust color mixtures accordingly, using Cyan more sparingly (Note that in some cases one color might be too dominant for the profile to balance. In such cases limiting the color in the density linearization is recommended).
Printer Profile are generally stable and do not need periodic refreshment. However it is recommended to create a new profile after changing printheads on the printer, replacing the medium by a different type of medium, or when the ink's version number changes, indicating a separate production batch.
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