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Article - Troubleshooting Color Workflows
The dreaded call every color manager fears? the swing shift tech calls the on-call manager to announce that the color is not coming out correctly. As you read this article on a calm Thursday morning, maybe you don't have any color issues right now - but if you've been in the business a while, you know that issues will show up at the time when they are least expected or wanted. We have written previously on ways to troubleshoot problems with displays and some printers.
This article is a more modern take on how to find the source of problems in looking at your broader, whole-system workflow. If you're interested, there are two older articles on trouble shooting Troubleshooting Color and Troubleshooting Color - Printers
My intent is to be broad enough to be useful to the many ways in which printing is done, while being specific enough to provide concrete steps toward finding solutions.
Many of the suggestions in this article can be used as preventative steps to take ahead of time that will vastly aid in diagnosing problems when they occur. If you run into a color problem that you can't solve, my boss would think me remiss if I did not mention that CHROMiX has a network of color consultants who can be brought into play to solve your color problems on-site or remotely.
What has changed?
Yesterday the color looked great. Today there is something off. What changed between yesterday and today? Don't immediately assume the most common culprit is to blame. Take a wide look at everything that might have contributed to a change in how ink gets onto your media:
- Was a new ink cartridge or formulation put into use a few days ago?
- Is there a new media stock being used?
- Were any inadvertent changes in the settings for your software? (You have backup documentation for all of your settings, don't you?!)
- Any software updates happen recently?
- Any operating system updates happen recently?
(Color profiles are inherently designed to work the same regardless of the computer operating system involved. But for RGB inkjet workflows, OS changes may introduce behind-the-scenes changes to the printer drivers and the way they put ink onto the paper.)
- What environmental changes have happened that may affect color?
- Are you seeing a change in your measuring instrument rather than a change in color on your print?
How do you know your measuring instrument is accurate? Can you verify it against another instrument?
If you have access to any of our software that supports instrument measuring (Maxwell, Curve+, ColorThink 4) you have the ability to use several different instruments to measure the same target strip, using the same target reference file. You are not tied into only using a target reference file that is intended for a single instrument. For example, you can use a target image and target reference made for an iSis to measure on the iSis, and also on an i1Pro, or Barbieri LFP, or a Spectrodens, or an eXact. It is not surprising that different instruments from different manufactures will record color slightly differently, but knowing what you can expect is useful.
Out of this gamut
Consider the basics. If you are struggling with a color that seems to be printable, but you find you're not able to hit it - have you checked to see if it is within the gamut of your workflow? There is a more extensive test of this below, but at the very least you can check your image against your profile in a 3D grapher. We have come to expect that our more saturated colors might fall out of gamut, but some colors are surprising hard to hit in other parts of the gamut. Consider a brown or a dark orange for example: Some colors that seem to be easily in gamut can be out of gamut when viewed in 3D.
Buy One, Get One
A smart choice among many manufacturing companies is to always buy at least two of any major equipment purchased. Down the road, the ability to troubleshoot mechanical issues is made much easier. If one machine is running well (ie: producing good color) and the other one is not, it is an easy thing to swap components out from one to the other until you hit on the cause of the difference. This makes for a quick diagnosis by the in-house maintenance techs, and a replacement part can be ordered & installed in a fraction of the time it would take to have the manufacturer's representative come in and fix it. It is hard to emphasize enough the value of this opportunity with multiple printing equipment around your shop. There are obvious benefits to troubleshooting color issues, but there is also substantial cost savings in duplicated consumables, reduced training times, and overall maintenance savings when dealing with identical machines.
Give a RIP
How do you know if your RIP is the source of your color problems?
There are ways of verifying whether or not your RIP is doing a proper job of applying transforms to your color. Try one of the ?RIP alternatives? below to see if these result in the same color as your normal workflow.
Use Photoshop as a RIP
For testing, you can use PS as a means of applying your RIP's profiles to an image and then run the image through your workflow with all color management disabled (but not typically calibration, unless you're testing it as well).
- Bring any number of sample images/ test images into Photoshop.
- Set up Photoshop to have your shop's input profile as the working space profile
- Use the convert to profile option (Edit > Convert to profile) to convert your test images from the input profile to your output profile (printer profile)
- Save out the images
- Run these images through your RIP - with the color management part of your RIP turned off (so no profiles are used in the RIP.)
What you're doing is having Photoshop handle the actual conversion of colors instead of your RIP. You're using the same profiles, but the conversion is done using Photoshop. Granted, there may be some slight differences between the PCS used by Photoshop and your RIP. But generally that is small enough to not make a visible difference. However, much can be learned if this Photoshop way of handling the conversion turns out different (or better!) than the way your RIP is doing it.
If the Photoshop method comes out looking good, that's a confirmation that your profiles are doing their job well.
If the Photoshop method comes out looking the same as what you get directly through your RIP, then that is some confirmation that your RIP is working properly and your color issues might lie elsewhere.
ColorThink as a RIP
Many readers of this newsletter are rabid fans of our ColorThink software.
ColorThink can be used to emulate just about any kind of workflow you can imagine. Here's an example:
- Bring a sample image into the Worksheet
- Apply an input profile to the image. (If your image has an input profile assigned to it already, this will already be shown in the Worksheet.)
- Drag and drop your output profile onto the image, and ColorThink will create a transform to convert the image to the color space of your printer.
- Choose the proper rendering intent for your workflow
(Optional:)
- Create a color list of important colors in your image by choosing them with the eye dropper tool after step #2, and follow the numbers through the transform.
The Worksheet is showing the history of the pixels of your image. For example, the original image from your client may be an RGB image with several colors out of gamut for your printer. Working from left to right, the Worksheet shows the transformation from RGB to Lab space, and then from Lab to your CMYK printer space.
The image under the printer profile column is color corrected by ColorThink to emulate the proper colors (as accurately as your monitor can produce them). This image should look very much like your finished output. If this does not match what you are seeing with your actual output, then:
- Something might be internally wrong with your RIP
- Your RIP might not be applying the profiles correctly
- A setting in your RIP might have been changed
- One of your profiles (probably the output profile) might be no longer valid as a description of your printing state. You would need to re-profile if everything else is in a stable state.
Checklist
Here is a checklist that we make use of here when tracking down color issues. Hopefully something in this list will shake out an idea for which direction to go to start your search.
Check for mechanical issues. Ensure that your equipment is in good working order. Calibrate, maintain, change the blanket or run a nozzle check pattern depending on your equipment - but the first line of defense is to bring your equipment back to a state of being in good running order.
Is your monitor calibrated? (Important if you are using a display to make color decisions.)
What section of the color space is the wrong color? Just the whites? Shadows? Neutrals? Does everything seem off, or only a few specific colors? Oftentimes identifying exactly what colors are affected is key to determining what the cause is.
How does the soft proof compare to the final print? (See this article for inspiration for using soft-proofing in your workflow.)
Is the color problem related to the location on the print? Is it at the leading edge of the sheet or the trailing edge?
What are the lighting conditions you are using to determine your color? Do you have color-balanced lighting? Does the color of the print look different when you stand next to a window? See this article
Have you verified that you are following the proper settings/procedures for your workflow?
Are you using a good test print? Making color decisions based on a single bad image is fraught with danger. Fixing that one color might throw the others off. Using a test image with a wide range of known, dependable colors is good insurance against that. Test Images
Good luck and good fortune to all as you solve your color mysteries!
Patrick Herold
CHROMiX, Inc.
To read this article with images in ColorWiki, click here
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