In this post I wanted to shed some light on the internal color calibration feature that is built into many of Canon’s professional photo printers. While Canon user guides explain how such calibrations shall be performed, I was not able to find good documentation explaining the concepts and recommended workflows for using it, especially in regards to the relation to ICC profiles and custom media types. This post is trying to fill that gap, based on information collected from different Canon manuals, my own experience and research and discussion in online forums, especially Luminous Landscape and Digital Photo Review.

The internal color calibration comes as a feature of the following printers:

• imagePROGRAF PRO series:
  PRO-1000, PRO-2000, PRO-2100, PRO-4000, PRO-4000S, PRO-4100, PRO-4100S, PRO-6000, PRO-6000S, PRO-6100, PRO-6100S
  

• imagePROGRAF iPF series:
  iPF6400, iPF6450, iPF6400S, iPF6400SE, iPF8400, iPF8400S, iPF8400SE
  

Note on third party inks: the baseline the printer is using for the internal color calibration is based on original Canon inks. When using third party inks the internal color calibration cannot be used and instead color management should solely rely on regularly updated ICC profiles.

To conclude this introduction, here a brief overview of the sections of this post:

• The Basics
• So How Does This Relate to ICC Profiles?
• Common and Unique Calibration
• Executing Calibration
• Target Values and Adjustment Values
  
• When to Execute Calibration
• Custom Media Types
• Final Words

The Basics

First, what is the aim of color calibration? To quote Canon:

“Color calibration improves color consistency by compensating for slight differences in how color appears when printing due to individual variations or aging among different printers.”
[Source: Features of Color Calibration Using the Printer Sensor]

So, the goal of the internal color calibration is to keep print quality stable over time and achieve a higher consistency of print quality between different printers of the same model.

The following figure shows how the internal color calibration works. It is being triggered by the operating panel or via the Canon Quick Utility Toolbox software and then takes place solely in the printer itself, with the printer printing a test chart, scanning it and calculating and storing the resulting adjustment values:

Executing the internal color calibration

Also during the printing process, the adjustments are applied by the printer itself, without involvement of the printing software:

Applying adjustment values during printing

Note: the terms Printing Engine and Calibration Engine are not used by Canon but have been introduced by myself to identify the parts of the firmware dealing with printing and calibration.

So How Does This Relate to ICC Profiles?

Even when using the internal color calibration, you still need ICC profiles.

An ICC profile describes the color space a printer is able to output on a specific paper, and tells the printing software how to adjust color data to achieve correct colors and accommodate the limits of the printer’s and paper’s gamut. There are generic ICC profiles for specific printer models and papers, often provided by printer or paper manufacturers, or you can create individual ICC profiles for your specific printer, which account for variations between different printers of the same model.

ICC profiles remain mandatory for any color-managed workflow, but the internal color calibration with its much easier handling can complement them by providing consistent and stable output on the printer side. For example:

• Variations over time: creating an ICC profile is more effort than running the internal calibration. So a good practice is to run the internal calibration, then create an ICC profile and then over time regularly use the internal calibration to keep the output stable and true to the ICC profile.

• Variations between printers: internal calibration can be used to cover variations between different printers of the same model instead of individual ICC profiles. Running internal calibration on all of them achieves consistent results between the devices, and an ICC profile created for one of them can then be reused for all of them.
  

The following figures show how ICC profiles are created and applied. Compared to the internal color calibration, creating an ICC profile is a bit more complex, with a test chart being printed via printing software, and profiling software with an external spectrophotometer reading that test chart and generating an ICC profile:

Creating an ICC profile

During the printing process, the ICC process is then typically applied via the printing software, for example Canon’s Professional Print and Layout or Adobe Lightroom, but could also be applied by the printer driver. As shown in the figure, if the internal color calibration is used, the printer would still apply the adjustment values to the print job.

Applying the ICC profile during the printing process

Common and Unique Calibration

In this section we’ll take a look at the two adjustment types of internal color calibration, the Common calibration and the Unique calibration.

• Common calibration: is executed with one media type (Canon) and will apply calculated adjustment values to all media types, including custom media types for third party paper, except any media type for which a Unique calibration has previously been executed.

• Unique calibration: can be executed with one media type (Canon and custom media types for third party paper) and will store adjustment values only for the media type it is executed with. Running Unique calibration will provide more accurate results for the specific paper.

[Source: Adjustment Types of Color Calibration, PRO-4000 Online Manual]

For the built in media types for Canon papers, it is predefined whether they support Unique calibration or are part of the Common calibration only. For custom media types you can either create a Calibration Target, after which they will support Unique calibration. Custom media types without a Calibration Target cannot be used for calibration, but will still be affected by Common calibration. And finally there are also generic media types, for example Highest Density Fine Art paper, which also cannot be used for calibration but will still be affected by Common calibration.

The following screenshots show this, the first for Canon’s Photo Paper Pro Luster, which in the PRO-1000 printer is set to Common Calibration, while in the second you can see that Canon’s Photo Paper Plus Glossy II does support Unique calibration. The third screenshot shows a generic media type for matte fine art paper, the fourth a custom media type without a Calibration Target, and the fourth a custom media type with a Calibration Target.

To find out which media types support which adjustment type in your specific printer you can either check on your own using the Media Configuration Tool, or check your printer’s manual, for example here for the PRO-1000.

So, when to use Common and when to use Unique calibration? Unfortunately there is no recommendation from Canon when Common calibration is sufficient and under which circumstances Unique calibration may have advantages. From a users perspective it is hard to qualify or quantify the advantage individual Unique calibration may or may not have. The circumstances requiring internal color calibration are difficult to simulate and the gains probably being relatively small, requiring elaborate tests to being identified. But still I’d like to share my own take on the topic:

• If you are using one or more Canon papers for which the media type is set to Common calibration, then you will need to use Common calibration to cover those papers.
  

• Common calibration should be sufficient under most circumstances, but if you want to make sure to get most precise results, and don’t mind the additional effort, use Unique calibration for those Canon papers that support it.
  

• If you use third party papers with generic ICC profiles, e.g. from the paper vendor, then Common calibration is all you need. You will not know the state of the printer that the ICC profiles were created on, so you do not have a precise calibration target anyway.
  

• If you use third party papers with custom ICC profiles created for your printer, again, use Unique calibration if you need the peace of mind of getting the most precise results, otherwise stick to Common calibration.
  

• If you are not regularly using any Canon paper supporting Common calibration, you either need to stock one of those for calibration only or need to use Unique calibration for all the papers you use.

For Canon papers, Unique calibration can be run without any preparation. For third party papers it is necessary to setup custom media types with Calibration Targets instead of using generic media types, see also section Custom Media Types further down below.

Executing Calibration

Calibration can be executed either via the operating panel or via the Quick Utility Toolbox. For details you can refer to Canon’s documentation, for example here for the Quick Utility Toolbox or here for the Operating Panel of the PRO-1000.

Calibration can be executed only with media types that support either Common calibration or Unique calibration (see above). Which media type you use for calibration will automatically determine the adjustment type. If you run calibration with a media type set to Common calibration, a Common calibration will be will be executed, affecting also other media types. If you run calibration with a media type set to Unique calibration, the calibration will only be executed for the specific media type.

Also important, Canon gives some recommendations on how the execution shall be performed:

• Environmental conditions should be stable and within the limits of 15-30° C temperature and 40-60% humidity.

• The printer should not be exposed to sunlight or other strong sources of light.

• Print head cleaning or print head alignment should be performed before the calibration.

• If possible, the same paper used for normal printing should also be used for calibration.

[Source: Performing Color Calibration Using the Operation Panel, PRO-1000 Knowledge Base]

Target Values and Adjustment Values

During the execution of the calibration, the printer compares the test chart against target values and then stores adjustment values for each media type the calibration applies to. The target values are also stored with those media types that support either Common calibration or Unique calibration (see above). For the Canon media types, these target values are preset by Canon. For custom media types, these target values are set when the Calibration Target for the custom media type is created.

The following two figure show this aspect of the calibration process, the first one for the Common calibration, the second for the Unique calibration:

Calculating and setting adjustment values during Common calibration …

… and during Unique calibration

When to Execute Calibration

So far we have covered a basic explanation of how the internal color calibration works and how it relates to ICC profiles. Now we will take a look at how to incorporate the internal color calibration into a color management workflow, specifically when it shall be used and which adjustment type to choose.

So, when shall internal color calibration be executed?

The following list is based on Canon recommendations, with some additions of my own:

• After initial printer installation,
  

• After printhead replacement,
  

• At regular intervals, when a certain amount of printing has been executed after the last color calibration was executed (indicated by the Execution Guide available on some printer models),
  

• Before a new ICC profile is created,

• After a significant change of environment conditions (temperature, humidity), e.g. moving the printer from a living space into a cellar or
  

• If colors seem different from before, despite using the same printing environment, under the same conditions.

[Source: Color Calibration Using the Printer Sensor, iPF8400 Online Manual]

The following flowchart visualises this, showing under which circumstances calibration shall be performed, and also for each case if Common and/or Unique calibration shall be performed.

Custom Media Types

Custom media types for third party papers make setting the different paper handling parameters easier and less error-prone. Check out my blog post on media types if you’d like to learn more.

The following figures show workflows for creating custom media types and setting them up for color calibration. The first workflow configures the media type for Common calibration and uses either a generic ICC profile, e.g. from the paper manufacturer, or a custom ICC profile created individually for your printer/paper combination. The second workflow creates a Calibration Target for Unique calibration, which I only recommend in conjunction with creating a custom ICC profile.

Workflow for creating a custom media type with Common calibration

Workflow for creating a custom media type with a Calibration Target for Unique calibration

Note: when creating ICC profiles for custom media types with Common calibration, it is important to always first run calibration to set the printer to a known state (target values) and then create new ICC profiles. For custom media types with a Calibration Target for Unique calibration, the target values are determined when the Calibration Target is created, and the first ICC profile should be created either right before or after that. After that, if a new ICC profile is created for the media type, calibration needs to be run beforehand.

Final Words

The internal color calibration is a powerful feature of Canon’s professional photo printers, but unfortunately the documentation is lacking when explaining the concepts and workflows behind it. I hope this post is able to fill this gap a little bit and useful to those interested in learning more about internal color calibration. Since I gathered the information presented from many different sources and also added my own interpretations, I’d be very happy to receive your comments, views and any corrections in case you think I went wrong somewhere. You can contact me here.