Colour Printing

How to Troubleshoot Colour Issues on a Digital Press

1. Check Environmental Conditions

You cannot get accurate colour if environmental conditions are out of spec! Digital presses are designed for optimum operation when relative humidity is within the 30%-60% range and it is room temperature. You cannot achieve accurate colour when humidity drops below 25%. Buy a hygrometer (humidity meter) and thermometer and measure before going to the next steps.

Colour on paper will shift dramatically if there is too much or too little humidity. If paper is not stored in sealed packaging it can absorb moisture when air conditioning is turned off over the weekend. Most complaints occur on Monday mornings in the summertime. Humidity often drops below acceptable levels in the wintertime and must be controlled with humidifiers or misters to get optimal results.

2. Check Digital Press

Download the drum test to check your printer/copier. This file contains one page for Cyan, Magenta, Yellow and Black plus instructions. Examine the output for defects. if there is a defect in one colour replace that drum. Defects in all colours will require a service call.

3. Print a Test File

The Quality Control Document will help you judge how accurately your printer is reproducing colour. You can download the file directly to your RIP to make sure your printer is producing accurate colour. Use GRACoL 2006 Coated for the CMYK profile and sRGB for the RGB profile with 24 lb Xerox Colour Xpressions. The GRACoL 2006 Coated profile can be downloaded from Idealliance.org if it is not on your RIP. Idealliance.org develops printing standards like SWOP and GRACoL 2006 Coated  for North America. Most new digital presses will use GRACoL 2006 Coated as their default CMYK profile. GRACoL has a wider colour gamut than SWOP so the full range of colour that digital can produce will be used.

Instructions

Make sure your printer is calibrated before running this test!

The digital press must be calibrated before printing the Quality Control Document. Do not calibrate first thing in the morning. At least 25-50 sheets must be run before colour stabilizes on the digital press in the morning.

Quality Control Document

Print the Quality Control Document each day after calibration and keep it as a record of the day to day condition of your digital press. Small variations are normal and major changes will indicate equipment or environment problems. Your service rep can review each day’s document to determine what is causing a problem and when it started.

If you get good results when printing the Quality Control Document then the print engine is working well otherwise service is required. If this document looks good and you are still having colour problems then there is a problem with the files being sent to the printer or the colour profiles are not setup correctly for your workflow. Your workflow or the files need to be fixed. If you don’t know how to fix your workflow, your Xerox sales rep can contact the Xerox colour consultant for your area. The Xerox colour consultant can assess your workflow and prepare a proposal for the services required to fix the problem.

How to Evaluate the Quality Control Document

This document should be reviewed under D50 (5000 degree kelvin) lighting. If you do not have D50 lighting use sunlight. This document will often show a magenta colour cast when viewed under fluorescent lighting.

The faces should look natural. People know how fleshtones should look and can instantly determine if there are colour problems.

Flesh tones should look natural and you should be able to see detail in the black dress. The food should look natural with saturated colours in this image.

The Pantone Coated swatches in the top row are out of gamut and cannot be replicated using CMYK colorants. They will not match a Pantone Coated swatch book. The Pantone swatches in the bottom row are in gamut and should match a Pantone Coated swatch book.

The IDEAlliance ISO 12647-7 Color Control Wedge 2009 can measured using a spectrophotometer to verify your digital press is meeting the standards for printing in North America. The reference file can be downloaded from Idealliance.org to use with your spectrophotometer.

The G7 calibration strip is used to verify gray balance. You should see even steps in the gradients with this image. The top row is black only. The bottom row of patches are a mix of cyan, yellow and magenta and it should appear gray under D50 lighting. It may have a magenta cast under fluorescent light.

In these CMYK gradients, you should be able to see steps in both the highlights (0-12) and the shadows (88-100). The steps should be consistent across all colours. For most machines in good working condition, you will be able to see colour down to 2 or 3%. Some machines will achieve 1%. There should a difference between 88% and 100%. You can fold the paper to compare 88% and 100%.

4. Check Your Media

To get the best results you must use media that is designed for your toner/ink and paper combination.

You cannot get accurate colour with the wrong media or media that has not been stored correctly!

Paper must be designed for copiers and digital presses. Offset and bond papers will not give you accurate colour. Colour on offset papers can vary dramatically between the front and back side. Some offset papers will not calibrate on digital presses. Contact your paper supplier and ask for digital papers. Paper that has not been kept sealed can absorb moisture or become too dry and you cannot get accurate colour.

Review the Materials Usage Guide (MUG) and Recommended Materials List (RML) for digital press from Xerox.com to learn more about using and storing paper.

5. Check Monitor Setup

Many people expect prints to match their monitor. You cannot match every colour that can be displayed on monitor! A high quality calibrated monitor and software that can soft proof will do a better job of simulating print jobs. Software from Adobe and Quark can soft proof print jobs. Office software does not provide any control for colour.

Example of unprintable colours.

Visual Method

Download RGB Calibration file to check your monitor. It contains memory colours, flesh tones and neutral greys. The sky, trees and fleshtones should look natural. The greys should be neutral with no colour casts. If the colours do not look right you need to adjust your monitor. Adobe Photoshop comes with Adobe Gamma to assist in visual adjustments. Use the Ideal method below for critical colour in graphic arts environments.

Ideal Method

You will need a high quality monitor for proofing and calibration equipment. Examples of calibration equipment are the Pantone Huey, X-rite EyeOne Display and Colorvision Spyder. X-rite also offers software for profiling all your devices.

6. Check Software Settings

Software like MS-Office does not provide any controls for colour management. There is very little you can do to manage colour with these types of applications.

Graphic arts software from Adobe and Quark can provide a extensive controls for colour management. The problem in most print shops is that colour management is not setup correctly, if at all. I often find several graphic artists in print shops using different colour settings. Sometimes they have different colour settings for each application! To get good results colour management settings for each application and device must be consistent. If your CMYK profile is GRACoL it should be used in each application and on every printing device. Your customers should be tagging their jobs with the profiles they are using so you can accurately convert colours to the working colour spaces you use for your applications and printing devices.

Instructions

In the Adobe Creative Suite open Bridge and check color settings. Make sure the appropriate colour profiles are selected and they are synchronized. In Quark Xpress go to Edit/Preferences/Quark CMS to check your setup.

On your printing devices check the profiles in use to make sure they match your applications and paper and ink combinations.

7. Compare colour in file to printed colour

I often get complaints that the current job doesn’t match a previous print job. After investigation, we find out the current job is accurate and previous job or proof is incorrect. The digital press wasn’t calibrated when the initial job was printed but the inaccurate print is what the customer saw and is expecting. This is a major problem that can be avoided with daily calibrations.

When the above steps don’t fix the problem, compare the colour in the file to the colour on the printed sheet. Sometimes there is a problem with the file, sometimes the printed colour matches the numbers in the file but it isn’t what you expected.

Procedure for Pantone colours

Make sure digital press is calibrated before you start. You will need a Pantone swatch book that has both spot colours and CMYK equivalents. Some Pantone spot colours are outside of the CMYK gamut and cannot be printed. Open the file and check the Pantone number for the colour. Compare the printed colour to the Pantone swatch book.

Procedure with other colours

You will need something like a Xrite EyeOne and EyeOne Share (free) or ProfileMaker 5 for this procedure.

Measure the colour in the file using the eyedropper or other available tool. Print the job make sure the digital press is calibrated and all the colour profiles/settings are correct. In EyeOne Share you can enter numbers from the file to create a colour swatch. Use EyeOne Share to measure the printed colour. EyeOne Share has tools to calculate the Delta E (the difference) between the two colours.

Downloads at Xrite.

8. Get training to improve your skills

Xerox and the IDEAlliance are offering the Digital Colour Management Certification Course. Part I of the course includes 20 modules of online training covering all aspects of colour management in digital printing. The course is hosted by Dr. Abhay Sharma of Ryerson University in Toronto. Part II of the course is hands on and is presented by your local Xerox Colour Consultant. Contact your Xerox sales rep for more info and pricing.

Send File for Testing

Use this form to send a file for testing.

Service Testing Files

This zip file contains the service testing procedure and test files for doing a thorough test of your digital press.

Download Service Test Files.
Bill Atkinson Test File

  • Torben
    #1 written by Torben 1 year ago

    Great information, Thanks for sharing

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