Calibration and Profiling

Our first reader question!

"Hi great blog, I've learned a lot already. I thought I would ask you a question that confuses me - what the heck is the difference between calibrating and profiling a color printer? The technicians talk about it like they are the same thing. Is that the case?"
~ Daniel M. - Pelham Print

Hi Dan, thanks for asking. The short answer is - Calibrating is putting the device into a known, stable state, a benchmark. Profiling is using that benchmark as a translation filter at either end of the color work flow.


Maintaining a reliable color environment is essential for the production of accurate and consistent color every time. To achieve a reliable color environment, calibration, profiling and measurement of output devices are critical. A number of affordable solutions exist today that combine all the hardware and software essential to these tasks. To be successful, it’s important that all of the elements in the Color Management work flow are speaking the same language or integrated with each other.

Color management works by two key process - calibration and profiling.

Unfortunately the two processes are often confused with each other, and consequently many people have a poor understanding of what they're all about. It's quite simple really, and this page aims to explain the difference and give you an idea of what's going on, at a basic level, in colour management.

Put simply:

• Calibration sets the device into its best native state using its hardware controls. 
• Profiling is the process of measuring and fixing up any remaining inaccuracies in its colour output (by modifying the signal going into the device). 

Calibration is using hardware adjustments on a device to set the device into a known, repeatable state (ideally close to some absolute benchmark for that device's behavior).

The frequency of calibration required varies on the print environment and its associated quality standards. In some environments, operators calibrate devices daily or every time that they start a new job or introduce a different paper into the production environment. In other cases, devices may be calibrated on a daily, weekly or even monthly basis.

When calibrating, certain output devices, such as those systems using Fiery, you don’t need to test it with a profiling solution to achieve consistent and/or accurate color. On other systems without Fiery’s capabilities, it is important to use a profiling solution to test the profile patches that go to the printer. Profiling is used to characterize the printer and to ensure optimum color output. Calibration is used to re-set the printer to this optimal desired state.

To help you understand what a profile does, think of it as being like a Photoshop adjustment layer or curve that is applied to and “fixes” the images you see on your screen. It is similar to a Look Up Table (LUT) that contains the "recipe" for converting from one color space to the colorspace of a particular device.
Profiling solutions generate ICC profiles that characterize the device, allowing a better understanding of its color capabilities. ICC profiles provide a cross-platform device profile format that ensures consistent, device-independent color throughout the entire Color Management work flow. Printer profiles are small files that describe the gamut (range of printable colors) of a specific printer's paper and ink/toner combination (they have a .icc or .icm extension).

Manufacturers typically ship output devices with default profiles, but many operators choose to develop custom profiles to achieve better color results for particular paper characteristics or the characteristics of the printing device.

A color measurement device reads the test pattern/patches. Since spectrophotometers are the most precise, they typically deliver the best results. The on-screen test pattern/patch results are compared to the numerical values associated with the test pattern.

Profiles are generally categorized in the followingways: input profiles (for scanners and cameras); display profiles (for monitors andprojectors); editing space (or working space) profiles, which are often embedded in digital files, such as JPEG or TIFF files; and output profiles (also known as printer profiles).

A solution such as Profile Inspector in Fiery Color Profiler then accepts the profile, and it is uploaded to an output device such as Fiery. This process allows accurate color to be maintained by the output device.

Why is Profiling Important?

Profiles help designers and others early in the Color work flow to better predict the way colors will reproduce at later stages in the process. This color control early in the Color Supply Chain saves time and decreases waste as the job progresses.

You can order standard profiles, or have custom ones built for you. Digital Dog is one such vendor, and ITSupplies builds them for inkjet.

Here is a link from Adobe to download most of the common North American profiles currently in use.

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Do you have a color management question, horror story or event to share?
Email me at reilley4color@gmail.com

Color Bars

Color bars are printed in the trim area and are used for quality control purposes by the printer.

Squares of colour are printed on the area of the page to be trimmed off, which the printing press operator uses to check colour density and consistency is maintained. This checking process is automated by some printers, with digital scanners tracking the colour bars to ensure quality and consistency is maintained.

• Unlike the live image area of the press sheet, color bars are consistent job to job. Therefore they are more efficient at providing a benchmark and can be used to track trends in variation over time.
• Color bars can be tailored to meet the needs and measurement capabilities of individual print shops.
• Color bars may be used to measure all aspects of the "print characteristic" - solid ink density, overprinting (ink trapping), dot gain, grey balance, as well as issues such as slur and dot doubling.
• Color bars can reveal issues with ink hue, blanket condition, impression cylinder pressure, etc.
• They can be used forensically to help understand why a specific job did not meet expectations.
• They are efficient since, unlike the live image area, they are a constant made up of well defined elements that continue from proof to press sheet.

An offset printing press is essentially a complex machine for laying down a specific film thickness of a specific color of ink onto a substrate. The digital version uses toner electrically charged then fused onto paper. The ink or toner is metered out in zones across the width of the press sheet according to how much coverage is required for each color in each zone.

The trick is that if you are producing a critical spot color with a build of process inks, those inks and all associated print attributes need to be “spot on.” The best way to control critical press factors like density, dot gain, print contract, etc. is to measure as many color bar patches as possible.

Color bars can serve many purposes. They can be used to determine color accuracy against a given standard or to determine a proof’s accuracy against a final print.

Color bars also can be used to measure consistency for the duration of a long print run, from job to job when a print job is reprinted, or between two similar printers.

So, ranked in order of importance, here are the patches we suggest for a four color press color bar.

1. Unprinted substrate patch (to zero out substrate when necessary)
2. Solid patch for each process (and spot) color (needed for solid ink density (SID))
3. 3/Color Grey patches at multiple tone values
4. Mid-tone patch for each process color (to gather dot gain (TVI) values)
5. Process color over prints (needed to measure trapping efficiency of inks)
6. Additional highlight and shadow tone patches of each process color (for a 75% patch to calculate print contrast)
7. GATF Star targets or microline targets (used to visually evaluate for press slur and doubling issues)

The items listed above are important and truly necessary, but if space is an issue, start with No. 7 and work backwards removing items until the bar fits. Also, items 3 and 4 could be easily reversed, but having one without the other makes diagnosis of grey balance issues difficult at best.

Grey balance targets

Grey balance targets are made up of a patch of three screened process colors that are balanced so as to appear as neutral grey under standard printing conditions. They are typically printed adjacent to a black screen tint of a similar value to allow for a quick visual, or measured, evaluation of how grey balance has shifted.

Grey balance targets can be useful since variation in any of the three process colors because of dot gain, slur, doubling, density, trapping, and registration will be reflected by a shift in hue away from neutrality. The 3/C patch will take on a bluish, reddish, or greenish color cast.

The idea behind this target is that any grey balance color shift away from neutrality suggests a possible color shift in the live image area. However, in production printing the grey balance target may not be a reliable indicator of presswork issues.

Color bars are not a requirement for quality printing, however, they are key to making proofing and printing more efficient and effective while reducing overall production costs.

Color bars are available from a variety of sources, including IDEAlliance (at no charge) and iStockPhoto.

Many imposition packages also include color bars in their imposition templates.

Another option supported by industry standards is the Ugra/FOGRA Media Wedge CMYK, which monitors the quality of digital proofs. It also can serve as a digital control aid to monitor the effect of imaging in CMYK mode and other prepress work.

The CMYK tonal values of the Ugra/FOGRA Media Wedge are based on ISO standards. The Ugra/FOGRA Media Wedge is available for purchase from FOGRA.

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Do you have a color management question, horror story or event to share?

Email me at reilley4color@gmail.com