Welcome to our first blog!
Printer calibration is required for any print device in order to get it into a stable, repeatable state. This is necessary as it enables you to bring the printer back in line, so to speak, as it will drift over time. Basically once you have the calibration process down pat you will be able to produce predictable, accurate and repeatable colour. The idea is that if your colour starts to move away, out of tolerance, a quick check of the calibration, re-calibration or adjustment of the calibration will bring the colour back into 'line', without the need for complete re-profiling, etc...
For the wide format market, covering display, signage and the like, I am not going to be specific about the substrate or media, printer type, ink set and RIP type in use. There so many combinations it would take more than a month of blogs or more to cover...
Good colour management strategy dictates that you should always calibrate your device first before creating your ICC profile. This is colour management 101!
Calibration - the process of bringing a colour device (i.e. monitor or display, printer, and even a scanner...) into an optimal, quantifiable, repeatable state. This condition could be an industry standard, manufacturers spec or guideline or your own specification.
With wide format printer calibration the printer will be controlled by a RIP, and the RIP will usually have an in built calibration process prior to creating an ICC profile.
The steps of calibrating the printer will usually follow, but not always, this order:
- Per channel ink limits
- Linearisation (tonality)
- Overprint ink limits
- Grey balance
- Profile creation
- Profile and colour management validation
Per channel ink limiting is usually the first step. This about achieving ink-media compatibility for each of the inks, per channel, C, M, Y and K. Too much ink being laid down can cause problems such as puddling, ink not drying, and ink reticulation. To achieve the goal here you are looking for the optimal result - enough ink with out causing problems, together with enough ink to produce enough saturation larger than the target gamut you are aiming to simulate. This step usually involves visual assessment and may include measurement using a densitometer or spectrophotometer.
Linearisation and tonality can follow as the next step, and may involve the set up controlling the mixing of light inks with the normal inks - i.e. light cyan with cyan and light magenta with magenta. Tonality or tone distribution is about achieving smooth and even tone graduation from 0% to 100% for each primary channel C, M, Y and K. This step involves visual assessment and will include measurement using a densitometer or spectrophotometer.
Overprint ink limiting is about looking at the build up of ink once the primaries (CMYK) are mixed together in different combinations - i.e. 100% M and 100% Y for RED. This step usually has a complex looking chart with rows of ink channel combinations in varying amounts. This step definitely requires visual assessment. Similar to per channel ink limiting except you are looking to find the step in each row that can produce the 'best' result with showing problems (ink puddling, not drying, etc.). You will probably need to input your results and print again to confirm your settings are correct...
It is wise to confirm your calibration by outputting a calibration check chart or similar to confirm your calibration - per channel ink limits, tonality, overprint ink limits and grey balance. I prefer to use a custom chart I have created for this purpose. It also helps you to decide on some important profile settings, such as total ink coverage and black start point. If the output of the calibration chart looks ok you can proceed to creating your ICC media or substrate profile.
Output your preferred CMYK profile chart - I like to use the IT8.7-4 chart - 1600+ patches. Measuring and building your profile really requires another blog as there are quite few options for measuring and then the settings for building your profile. Suffice to say once this step is complete you should be looking to validate your profile and validate your colour management settings in RIP, using your new media profile. This does involve critical visual assessment, under the correct lighting, and spectral measurement for reporting to see how your output now stacks up compared to an international print standard or an in-house standard. Again, I think it best to tackle this subject in a separate blog.
I hope this information about wide format printer calibration is helpful.
Please feel free to leave constructive comments and any relevant questions you may have.
David Crowther
Colour & Print Consultant
