There are a number of reasons why a colour validation test fails.
The gamut of the printing condition cannot match the gamut of the reference printing condition
An important cause for failure is that the colour gamut (a set of possible colours that can be produced) of the printer in combination with the used print substrate is too small to accurately simulate the reference printing condition. For instance, simulating a relatively large gamut like GRACoL 2013 Coated (CRCP6) on a water-based inkjet device on an uncoated media is likely to fail.
In this case, failing only means that the reference printing condition is not matched, not that the printer is functioning incorrectly.
Non-optimal printing settings
To obtain correct and accurate colour validation test results, it is crucial to print test charts with the correct colour management settings. Therefore, make sure to read the print instructions in the [Color tests] app carefully.
Mismatching measurement modes
For optimal results, the ICC output profile used to print a test chart needs to have been created with the same measurement mode as the one defined in the test specification.
Changes in the colour behaviour of the printer
If a printer has not recently been calibrated, you might notice a change in the colour behaviour of the printer. This change often results in less accurate colour reproduction and, therefore, poorer or failed colour validation test result. Failed colour validation tests might indicate that you need to calibrate the printer or media.
In rare occasions, the colour behaviour of a printer changes so much over time that it cannot be corrected with a calibration procedure. If this happens, a new ICC output profile must be created.
When a colour validation test fails unexpectedly, for instance on previous occasions the same test on the printer and media succeeded, you can perform the following steps to find the possible cause of the failure.
Verify that the printer and media have been calibrated recently.
If the printer or media have not been calibrated, perform the calibration and redo the colour validation test.
Inspect the measured test chart.
Does the measured test chart correspond to the conducted colour validation test? Check the meta data on the test chart (if any). If you measured the wrong test chart, redo the colour validation test using the correct test chart.
Is the media type in accordance with the test specification? If not, redo the colour validation test with the proper media.
Do you see any artifacts on the colour patches of the test chart? If so, redo the colour validation test.
Did you perform a media relative test and you observe colourant on the areas of the test chart that would normally be unprinted? Possibly, you used absolute colorimetric rendering intent to print the test chart rather than relative colorimetric rendering intent. Redo the colour validation test using the relative colorimetric rendering intent.
Did you perform a side-by-side test and you do not observe colourant on the areas of the test chart that would normally be unprinted? Possibly, you used relative colorimetric rendering intent to print the test chart rather than absolute colorimetric rendering intent. Redo the test using the absolute colorimetric rendering intent.
Verify the used colour management settings.
If incorrect print settings are used when printing a test chart, the colour validation test might fail. If the test chart print job is still available on the printer, verify the correctness of the print settings.
For side-by-side tests (including G7® Targeted tests), the following colour management settings are optimal:
Rendering intent is set to absolute colorimetric.
CMYK input profile is set to an ICC profile that matches the chosen reference printing condition.
Blackpoint compensation is off.
Black preservation is off.
For media relative tests (including G7® Targeted Relative tests), the following colour management settings are optimal:
Rendering intent is set to relative colorimetric.
CMYK input profile is set to an ICC profile that matches the chosen reference printing condition.
Blackpoint compensation is off.
Black preservation is off.
A G7® Grayscale test is typically performed on a G7® calibrated printer. The test chart is printed without colour management.
Did you use incorrect settings? Redo the colour validation test with correct colour management settings.
Verify the quality of the ICC output profile.
On PRISMAsync-based printers, verify the quality of the output profile with the help of the profile accuracy test. Make sure that the profile accuracy test is carried out on the same media that the test chart was printed on. If the profile accuracy test fails, replace the output profile or create a new output profile.
On systems that do not offer the profile accuracy test, replace the output profile. When needed, use the tool that you normally use to generate the profile.
Verify whether there is a gamut mismatch.
Check the colour difference values (△E76 or △E00) of the red, green and blue overprint patches. If one or more of the colour difference values is higher than 4, a gamut mismatch is likely.
Check the colour patches that are close to the darkest colours in the gamut. Large colour differences indicate a gamut mismatch.
Check the full tones: full cyan, magenta, yellow and black. Large colour differences indicate a gamut mismatch.
Check the colour difference of the substrate patch. A large colour difference indicates a gamut mismatch.
This can only happen in side-by-side tests since in media relative tests the colour difference of the substrate patch is zero by definition.
If the gamut of the printer is too small to accurately reproduce the colours of the chosen reference printing condition, this cannot be solved by calibration or profiling. It reflects a physical limitation of the printer and media combination.
Choosing a different media can result in a larger colour gamut. For instance, coated media typically result in a larger colour gamut than uncoated media.