Colour Management setup and maintenace

A predictable colour management system can take time to set up but the rewards will come with reduced waste, less time chasing colour and more time printing.

Set-Up

It starts by confirming that all RIPs are using the same reference colour space. GRACoL has become the industry standard for digital and sheetfed devices.

Check how your RIP software is handling spot colours. Are all of your workflows set-up to utilize the PANTONE Lab values? If you are running a UV or LED digital printer, have you categorized your common media into white point groups? On these devices it doesn’t make sense to have a profile for every medium, only the ones that have different white points. An example would be to make a profile for your yellower card and one for the bluer styrene. Then look at which other media share a similar white point to those two. Often you will only need two or three different sets of profiles. This makes it much easier to re-linearize or recalibrate when there is drift.

Evaluation:

How does one evaluate and maintain a colour management system on various printing devices? First you need to determine if you are in fact printing correctly, and yes, correctly can have many interpretations. But we can all agree that if you print a CMYK gray blend, it should be neutral and linear.

In Photoshop, create a new CMYK document and be sure to select GRACoL as the colour profile. Then create a linear blend with the blend tool and save as a PDF with no colour conversion. Print this blend to all your digital devices and view under D50 lighting.

Another way to evaluate colour is to create a gray swatch with a 3-colour gray circle. Similar to the gray blend suggestion above, a gray box is made with 50% cyan, 40% magenta and 40% yellow.

This very simple box can tell you many things when you know what to look for. Is the tonal relationship at the 50% balanced? If the lightness / darkness of the outside 50% K is similar to the inside circle, then you have good tonal balance. Now look at the inside circle. Is it neutral or does it show a colour cast? A few percent in one direction becomes evident when you look at the circle. In a well-balanced system the tone between the outside square and the inside circle will be the same and the neutrality will also be the same.

Be careful when sending this test through a digital device’s RIP. A RIP, when converting to the output profile will go from CMYK to Lab and back to CMYK and in this conversion the 50% K will be rebuilt with the GCR settings in the profile. Simply put, you can’t use this test on a digital device to test gray balance. It Is best used in an analog system that only uses curves, such as a press. A colour conversion can still happen at the RIP when going to press. Always check the values of the file after it has been ripped to ensure the dot values are what you expect. 

Maintaining Colour:

All too often profiles and press curves are set up and forgotten. Devices change – that is a guarantee. But how often they change will depend on a number of factors. What you need to know is when this change happens. This will allow you to stay ahead of the curve… and correct the deviation by re-linearizing or reprofiling before your shop spends extra time chasing colour.

Maintaining a colour management system requires you to collect data. This can be daily, weekly or monthly. The more often you are monitoring your devices the sooner you will catch a colour change.

There are a number of software programs that are designed to assist with this, or you can create a simple test form that includes the above images as well as the usual GATF and G7 imagery. Printing this right after you create new profiles or press curves will give you a baseline. Then reprint it and compare the original baseline in a light booth. If you can’t see a change then you are good. If the device is not working as expected, then it’s time to re-linearize or re-profile.

Keeping colour consistent needs to be a priority for management. Time needs to be allocated into your schedule to evaluate colour and maintain colour.

Angus Pady is a colour management expert working with FujiFilm in Toronto. He can be reached at angus.pady@fujifilm.com

 

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