By Bill Owen, G7 Expert/Color IT Specialist, Alder Color Solutions
Does limiting your ink sound counterproductive to creating an expanded color gamut? Over-inking is a common problem seen in the printing world, and especially when it comes to printing on fabrics. This misconception can wreak havoc for printers looking to optimize their gamut, as more ink does not necessarily mean more color. In most cases, more ink results in distorted color(s) and hue shifts.
Ink limiting and Dye Sublimation Printing
Dye-sublimation printing can be exceptionally tricky when it comes to color management, and the most important factor in producing great results is almost always proper ink limiting. To achieve this, understanding Chroma/Saturation is key, as well as ensuring you have the proper tools available in front of the printer—a good color management RIP and a highly accurate spectrophotometer for measuring printed colors.
The RIP should include color features that will allow you to create custom media profiles. During the process of creating a custom media profile, charts are printed onto the dye-sub paper (such as ChromaMax), then that chart image is transferred onto the fabric or substrate of choice. The charts are then measured with the spectrophotometer into the RIP’s color management “media profile creation” tool, where one of the first steps will be to limit the individual ink channels. In some cases, the RIP will tell you where to limit those inks, but the RIP software may not always make the best choice. For example, measurements may need to be taken in LCH mode—LCH is otherwise known as ‘chroma’ and chroma is another word for “saturation.”
These ink limiting color charts have color ramps, building from 0 to 100 percent of each primary color. Depending on the printer and the number of colors available, there could be numerous ramps to measure. Some prints have just four colors—CMYK—while others may have several more—orange, green, and violet, or red, green, blue, etc.
In order to determine where to limit inks, the first step would be to visually assess the color ramps. Often, there may be a visible hue change in the colors or place where they become very dark. This is where the focus should be. The best approach would be to measure each patch of the color ramp individually to find where the chroma peaks (that’s the C value from LCH measurement values). Another approach would be to analyze the LAB values, with attention to the L* number in the same manner—looking for a point where the patches stop getting any closer to zero or do not continue to get darker. From here, the patches beyond that point may seem to show a change in hue; for example, cyan might begin to look bluer. Changes like these are indicators that there is too much ink, and so much so, that the color or hue is changing.
Once a point in the color ramp is determined (where the color is not getting any more saturated) this is the point where ink should be limited. After individual ink limits per channel are established, the total ink limit, or combination of all CMYK values, will need to be evaluated. In one example, if Cyan is limited to 80, Magenta to 90, Yellow to 80, and Black to 90, the total ink limit comes out to be 340. When generating custom media profiles for fabrics, it is not uncommon to have a total ink limit of less than 200. During the process of ink limiting, it is also common to encounter a linearization step, as well. When ink channels are limited properly, the linearization step also works much better and you are sure to be printing nice neutral grays upon completion of generating a custom .icc/media profile.
Summary
Over-inking can lead to dark and oversaturated colors, and additionally result in a shift in color hue. Ink limiting, when done correctly, can help to expand a printer’s gamut and allow for better control over color. Let the numbers be your guide and trust your measurement device and data that is gathered. These are far better in addressing ink limiting challenges than the average eye’s capabilities.
About Bill Owen and Alder Color Solutions
Color IT Specialist and G7 Expert, Bill Owen has worked in prepress, printing, and color management for over 40 years, and truly enjoys color management, calibrating printing equipment to international and industry standards, as well as sharing his knowledge of print and color.
Alder Color Solutions is an industry leader in color training, Color IT, and in both hardware and software solutions for the print, textile, brand, ad, photography, and signage industries. Established over 20 years ago, Alder Color Solutions has grown into a global source for innovative color solutions.
