An open letter to monitor profiling software manufacturers.

Many monitor profiling hardware and software solutions make their way to the displays we use. Some are purchased, others sent for review.  In the course of testing and using these products, one aspect stands out: many applications are missing one or more features critical to performing the task at hand.  This is particularly true of entry-level products. Vendors have a tendency to eliminate features found in their higher end products in a haphazard manner. The result all too often is a product crippled to the point of uselessness. Recent revisions to some popular products have improved matters; it is with hope of further innovations that this letter is conceived.

This open letter to profiling software vendors sets down a minimum range of capabilities competent monitor profiling packages should offer. It is also a guide to photographers out to purchase profiling software on what to look for. The quality of profiles created by any software strongly depends on the quality of the measurement hardware and algorithms used. Software that implements all the features listed below still may fall short in terms of creating good profiles. Software lacking critical capabilities, however, is handicapped from the start.

An additional list of useful attributes follows. These are features that, while not essential, aid in refining the profile quality, make the profiling and calibration process easier, or are valuable for photographers or organizations with multiple workstations. A note to vendors: Using these items to differentiate between entry-level and high-end monitor profiling packages would aid the photographic community more than releasing applications having one or more serious omissions.

Perhaps we can influence some enlightened vendors in their product designs. Warning to such vendors: I'm going to point fingers at horrid examples as well as praise the good points. I am not out to bash or promote any particular product; I only aim to list what a monitor profiling kit should look like. This list also is not geared at the obvious; e.g. that the final profile must be of useable quality.

Essential features: All calibration systems should have these.

Calibration:

1. Provide both profiling and calibration. There must be the capability to use the sensor to guide hardware adjustments. On LCD monitors, this simply involves setting the backlight luminance. For CRT displays, both black and white points as well as color guns can be adjusted. The more adjustments are done at the hardware level, the less artifacts appear in the final view.
2. Use standard vcgt tags to store the calibration data. This even allows leaving Adobe Gamma as the calibration loader for Windows and OS 9 rather than installing a vendor-specific program and making the customer root out Adobe Gamma after each time an Adobe product is installed, upgraded, or patched.
   • If a proprietary loader is used, give it some intelligence. Store the video driver version, resolution, refresh rate, etc. in a custom tag. Check these values at system startup. If they are not the ones the profile was built for, pop up a notification dialog.
   • Validate that the calibration data are written correctly to the video card during the measurement and profiling stage. A simple check of black, middle gray, and white will suffice.
3. Follow the ICC profile format specifications. In cases where the V2 spec is more restrictive, follow it instead to maintain compatibility with older software. No more forgetting to adapt the chromaticity values to D50 or writing profiles with tag offset problems.
4. Allow customers to specify a desired luminance and adjust this target if necessary during the calibration phase. There is no reason why photographers need their eyes blasted out by overly bright displays. GretagMacbeth's ProfileMaker Pro and the new (version 3) Eye-One Match, ColorVision's Spyder2Pro and OptiCal, and Monaco Optix XR Pro not only allow specifying the display luminance, but use the measurement puck to guide the settings. Other packages, including BasiCColor Display simply let you select a luminance value. In most cases this suffices.
5. Verify that the black level is not so dark that all shadow details will be lost. This could be as simple as measuring patches at (0,0,0) and (10,10,10). If there is no difference, pop up a dialog box saying "hey bozo, your black level is set too low" or words to that effect.
6. Allow arbitrary white point and gamma values, not just D50/D65 and 1.8/2.2.
   • While we're at it, get rid of the gamma 1.8 default for Mac monitors. This made sense for the original monochrome Mac displays. It does not now. My suggestion for a default is D65/2.2 gamma.
   • Support calibrating to native white point for LCD displays. This maximizes the available color range. Let your customers know what this white point is.
   • Support calibrating to native (gray) gamma at least for CRT displays. This minimizes calibration-induced display artifacts including shadow banding and posterization. Again, report what the measured gamma value is.

Measurement:

7. Ensure the measurement window is adequately large so accurate measurements are possible on high resolution displays. There is no sense in having wonderfully sensitive instruments if all they measure is spillover from neighboring screen areas.
   • ProfileMaker 5 is marginal at high resolutions (2048x1536 on a 22” CRT) with the Eye-One Display. The smaller aperture of the Eye-One Photo and Spectrolino help here. BasiCColor Display 2.5 for Windows is hopeless.
   • Suggestion: Scale the measurement window with the display resolution.
8. Design the puck so it does not place pressure near the measurement aperture on LCD screens. Laptop displays in particular radically shift color with even light pressure.
9. Disable the screen saver and monitor turn-off during measurement if possible. At the least, blank the cursor image if it drifts into the measurement area.
10. Do basic data validation during the measurement process. This should detect gross problems such as the puck separating from (or falling off) the screen during measurement.
    • Basic stuff here: Is white lighter than black?

Profile creation:

11. Allow making both LUT and matrix profiles.
    • Sometimes one works better than the other; which one is often a matter of personal taste.
    • As a general rule, matrix profiles give more pleasing results on CRT monitors, while LUT profiles better describe the vagaries of LCD displays.
12. Offer to save the profile as the system default. BasiCColor Display 2.5 is the only package I have seen that omits this step.
    • Validate that the default is set correctly. ColorVision’s Windows products sometimes fail this test. I have sympathy here, as the relevant Windows GDI functions are largely undocumented and bug-laden.
    • Save the profiles in the correct location while you're at it.
13. Do not automatically append the date to the profile name. My preference is to default to the last-used name. There is no point in cluttering up your system with profiles describing a condition that will never exist again.
14. Perform basic profile validation against a limited target subset. Report average deviation in Delta-E (preferably dE-2000) and report an error if greater than some predefined value.

Nice to have features: Use to differentiate target markets.

1. Allow specifying the shadow set point and use the measurement instrument to calibrate to this value. The only reason this is not on the essential list is that many monitors and measurement sensors lack the necessary accuracy and stability. The software should complain if the black point is set too low. OptiCal allows specifying black level (a good thing) but does not fuss if it is set too low. I have seen many an OptiCal-profiled monitor where the brightness was so low that all shadow detail was gone.
2. DDC capability for DDC-enabled monitors. English translation: If the monitor brightness, contrast, and color guns can be controlled via software rather than just front panel button pushing, use it. Some monitors (e.g. Sony, HP) offer much finer control by software than manually.
   • If DDC is available, monitor the red level on required to meet the white point goal on CRT monitors. If it is at or close to maximum, notify your customer that the monitor is in need of replacement.
3. Write ICC Version 4 profiles. These are not fully supported on the Windows side, but do offer useful features.
4. Support a reasonable range of instruments. If nothing else, software vendors expand their market by supporting competitor's instruments. My suggestions:
   • Recent Sequel puck variants: Sequel Chroma, LaCie Blue-Eye, GretagMacbeth Eye-One Display 1, and BasiCColor Squid.
   • GretagMacbeth Eye-One Photo
   • GretagMacbeth Eye-One Display 2
   • X-Rite DTP92 and  DTP94 (Monaco Optix XR sensor)
   • GretagMacbeth Spectrolino.
   • ColorVision Spyder2.
5. Ability to set a desired contrast ratio equal to or less than what the display system is capable of. If DDC is present, allow on-the-fly switching of profile parameters to scale monitor contrast with the print system.
   • On DDC capable monitors, the maximum useable contrast range can be automatically determined given the upper limit imposed by the white luminance set point.
6. Trending and tracking of display performance over time Done correctly, this gives advance notice of a dying monitor.
   • Simply saving at least a subset of the measurement data is a start.
7. Display matching between monitors. I'm reluctant to add this one, although it does have its uses. Matching a series of displays entails setting all of them to the lowest common denominator; i.e. targeting the worst common level of performance. For larger shops with several monitors of the same type and vintage, however, this can make for excellent consistency from monitor to monitor.
8. Allow validation of the monitor calibration in different screen areas. This does not need to be as fancy as the Barco 25 point calibration, but would detect corner purity problems. If the monitor offered corner purity adjustments, the software could guide them. A two point measurement of gray and white (or perhaps just one) should suffice.
9. Perform a calibration check using a standardized set of colors. The GretagMacbeth ColorChecker D50 values, for example. Highlight any colors that are out of the display gamut and give a Delta E-94 metric for the rest. Doing a more comprehensive check is also useful, but showing an image of a standard reference target would be slick.
10. Use the puck to make a SWAG at the ambient light level prior to profiling. Complain if it is too high (allow the customer to disable future warnings, however). This may not work with all measurement devices.
11. Use the puck to measure the light level in a viewing booth and compare to the monitor white luminance. Either the monitor or viewing booth can be adjusted accordingly.
12. Support arbitrary profiling targets.
13. Dual monitor support. Build separate profiles for each display.
14. Profile curves editing. Did I mention curves editing? No. Take that out. Even with a top-end profile editor this isn't worth messing with. If the profile is no good, one of several things is at fault: The display hardware is dying, the calibration settings are incorrect, the measurement hardware is not up to the task, or the profiling software is not working well. Mucking about with profile curves is not a solution.

Ethan Hansen, October 2, 2004.

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