Ink Optimization with GCR

More Than Just Saving Ink

Ink optimization software has been with us for some time, but most printing plants do not use it. Many have not heard of it and are unaware of how the software works and what it does. Ink optimization software uses Gray Component Replacement (GCR) to change the separation of the image. The software will take color from the file, and increase the black channel. The software can be set to take more or less color out depending on the user needs. The most obvious benefit is reduced ink usage, but there are many other benefits as well. The function performed by GCR – the removal of color and replacement of black makes most people expect to see a color change in the resulting separations. What results however is a nearly identical separation.

This first benefit of ink optimization is the use of less ink to achieve an identical separation. It is common for ink reduction to result in a 10%-30% reduction in ink use and ink costs. While this appeals to the printing plant owners and finance officers, ink reduction is not the main benefit. These potential cost savings often are what get the product in the door. GCR is often used for purposes other than saving ink. Scanner operators often apply GCR to an image to make the image more neutral. This is also the case with ink optimization software except instead of just applying GCR to images; the software applies GCR to all elements, vectors and images. Beyond ink savings, the added benefit of applying GCR is stability. Not only does the GCR make the image appear more neutral but the removal of color and insertion of black makes the printed result more stable. This can be seen on press when running a job with GCR by adjusting an ink key. On the page without GCR the ink key adjustment is quick and obvious. On the page with GCR the adjustment has less of an effect and in case of high GCR almost no effect. This results in faster make-ready and improved consistency across a pressrun.

GCR software also typically adjusts the total ink limit or total area coverage (TAC). In the past when images and jobs where were touched in prepress this would be done by prepress operators. Today many files entering printing plants have unknown origins, and the GCR software can globally apply the desired TAC to the entire document. Take the example of a web printer – if a customer created a document in Adobe Creative suite with a TAC of 400%, the software would automatically adjust the file and all elements down to this plants desired TAC of 260. This means putting less ink on the page, which makes printing and control much easier for the press operators. An additional function of systems applying GCR is the ability of the software to perform gamut mapping. Many of the GCR systems are using device links (two ICC profiles used to make a direct color conversion) and because of this they can convert files from one color space to another. It means they can be used to make the press print to a standard print condition such as GRACOL or SWOP, as well as take advantage of ink savings.

While many printers still use press curves and a GCR system, with gamut mapping press curves are not always necessary. There are many parts of the print space (such as the ¾ tones) where it is physically impossible to perfectly match the print specifications. An even more powerful example of gamut mapping is the ability to move from one color space to another. For example if you are in a print process where you need to use a non-traditional rotation, such as moving the Y to another position, the GCR software can be used to map color so that the color of traps and other elements appears correct. In these situations it would be physically impossible to match GRACOL or SWOP but the color mapping will correct the values in the file so the press output will appear correct. (It can also be used to match your press to a customer’s custom proof condition.)

So to summarize the benefits of applying GCR on a job are:

Improved reproduction
Better neutrals
Consistent TAC
Less ink usage
Faster make-ready
Improved stability across the pressrun
Opportunity to perform transformations from one color space to another

Sounds great? Like anything else there are things to watch out for. Danger areas for GCR range from the simple and predictable to more complex behaviors. The most simple is that if you have less ink on the page then you will have less control. On a web press without closed loop color control less ink is helpful, as you have limited control over the color. On a sheet fed press, where you may be precisely adjusting the color during the press ok you may actually need the color on the sheet. Other complaints include occasional quality issues (rare but depending on the system and conditions possible). Other things to watch are if you are doing custom GCR based on press conditions (rather than a more generic GCR) you need to watch and adjust as your press conditions change.

Some software applications capable of performing ink optimization and GCR:

Please comment on your experience with use of GCR and any other ink optimization software you have found to useful.
Reproduced with permission from Printing in the Dark, Ron Ellis (2010-04-09)