X-Rite Chroma 5 PRO Colorimeter

The standard Chroma 5 colorimeter is an exceptional product. Its accuracy approaches the i1Pro and it offers reasonable speed and excellent low-light performance that is typical of this design.

It is also one of the easiest devices to use because it requires no dark reading calibration.

Despite this, it is an affordable mass-market device whose tolerances are higher than what you would find with more expensive professional color analyzers.

The Chroma 5 ships from the factory with two internal calibration tables, one optimized for general use and the other for CRTs.

We have developed a version of the Chroma 5, which we have named the Chroma 5 PRO, that offers substantially enhanced accuracy across a wide range of displays.

What we have done is provide a software-based refinement to and expansion of the existing calibration tables in the individualized license file delivered with each unit. To understand how this works, it is important to first understand the source of errors in tristimulus colorimeters.

In an attempt to accurately model human color vision, in 1931 the CIE defined the standard observer, which is characterized by three color matching functions, shown below.

A filter-based colorimeter attempts to mimic human color perception by matching these curves. However, accurately matching these complex curves using any reasonably affordable filters requires correction with a reference spectroradiometer. Otherwise, you cannot achieve the desired accuracy with different display types. A spectroradiometer does not rely on filters as a way of mimicking human color vision, but rather measures the spectra of a display directly. Its accuracy depends only on the bandwidth, sensitivity, and resolution of the device.

The inaccuracies of a filter-based colorimeter, such as the Chroma 5, arise from a variety of sources.

• To keep costs down, the standard and CRT modes that the factory Chroma 5 ships with are based on a generic correction from a 8nm Photo Research PR-650. The same correction is applied to all Chroma 5's.
• The affordable materials used in the colorimeter leads to some unit-to-unit variation.
• Over time, exposure to fluctuations in temperature and humidity further degrades the instrument's accuracy.
• There is a natural variation in consumer displays—even displays of the same type!—so the operating modes of the colorimeter are no more accurate that these variations allow. The calibration tables of the factory Chroma 5s can only be derived from the general performance characteristics of the display type, not the specific display being calibrated.

Taken together, these four sources of inaccuracy—generic factory calibration, unit-to-unit variation, degradation from exposure to the elements, and a lack of consistency among displays—result in a device that, on average according to our tests, typically deviates from a reference spectroradiometer in the range of 2-9 dE (CIELAB), depending on the display type and age of the probe.

Of course, the best way to minimize these errors is to use your own reference spectroradiometer to correct the Chroma 5 for each calibration session on a single display. ChromaPure provides an Meter Offset module for just this purpose. However, the vast majority of consumers cannot afford a true reference device, which are very expensive. SMPTE requires a reference instrument to have a minimum accuracy of ±0.002 for the measurement of xy chromaticity coordinates at any luminance above 3 fL. The only instrument capable of this level of precision is a 5nm spectroradiometer. A tristimulus colorimeter will not offer this level of accuracy, nor will an 8nm or 10nm spectroradiometer.

The Chroma 5 PRO virtually eliminates 3 of the 4 sources of error and lessens the fourth for a small fraction of the cost of a true reference device.

• First, we individually test each meter against a reference spectroradiometer on a CRT, several LCD flat panels, a plasma flat panel, and front projector with a standard UHP lamp.
• Second, we include correction figures in the individualized license file that align the standard Chroma 5's response to our reference device. These two steps alone greatly improve the built-in calibration tables for the Chroma 5 and completely eliminate any unit-to-unit variation.
• Third, for a modest fee, we will periodically recalibrate your Chroma 5 PRO to ensure it retains its initial accuracy. This service eliminates the problems associated with exposure to the elements over time.

Our experience has shown that the Chroma 5's accuracy is reasonably consistent when reading CRTs, plasmas, and front projector screens. The biggest problem by far lies with LCDs. Using the Standard mode the Chroma 5 may read one LCD very accurately and yet be considerably off on another. There simply is no consistency when reading LCDs. Contrary to one widely-repeated myth, this is not an issue directly related to the difference between CCFL backlit and LED backlit displays. Some LED displays actually give the Chroma 5 less trouble than their CCFL counterparts. Also, the Chroma 5 can maintain considerably different levels of accuracy when comparing two CCFL displays. The problem isn't with LED backlighting. The problem is LCDs period. To address this problem, the Chroma 5 PRO ships with 5 different LCD modes. We may add additional LCD modes as needed.