PrecisionColor Calibrator Q&A December 13, 1995


Q: Is the PrecisionColor Calibrator compatible with System 7.5.2, or Apple PowerMacintosh systems with PCI bus design?

A: The PrecisionColor Calibrator is not supported with any of the new PCI based Apple PowerMacintosh systems. There are no updates planned to make it compatible. (!n)

Q: What is the current calibrator software, and is it compatible with the Power Macintosh and System 7.5?

A: The current revision of the Calibrator software is 2.2, which is compatible with the original Power Macintosh series of computers. However, when calibrating on a Power Mac, the software will only run in emulation mode. The software is untested and unsupported under System 7.5 and later, and is known to have some compatibility problems in such systems. Technical Support therefore advises against using the PrecisionColor Calibrator with System 7.5 or later.

Q: I do all of my retouching in 24-bit, but I can only calibrate in 8-bit. What use is the calibrator to me, if it only works in 8-bit?

A: If you calibrate in 8-bit, those settings, and/or changes, will be reflected in 16-bit and 24-bit as well, since those settings are extrapolations of the original 8-bit color lookup table. Also, the length of time it would take to calibrate 16.7 million separate and distinct colors is substantially greater than the time it takes to calibrate 256. Furthermore, the calibrator isn't really calibrating 256 colors. It's calibrating 256 shades of red, then 256 shades of green, then 256 shades of blue, therefore accomplishing the 24-bit calibration since 256x256x256 is 16,777,216.

Q: The calibrator software asks if I want to enter a "wait state?" Why would I do this?

A: The calibrator software defaults to zero wait states since the assumption is that your graphics card is fast enough to handle the NuBus speed of your computer. If, however, you have a very slow graphics card (unaccelerated), you may have to enter a wait state for the calibration to be effective. If not, some of the shades of R, G, and B may not be measured as the graphics card starts to play catch-up with the processor. A good rule of thumb is to enter a wait state if your graphics card is unaccelerated, can't act as a frame-buffer, or was manufactured prior to 1992.

Q: When I click on the "display type" setting in the calibrator software, my display isn't listed. Can I calibrate?

A: Yes. If the display is not listed, then there is another display listed that uses the same CRT and associated phosphor settings. Look at the manual for your display, and see what CRT manufacturer was used, then look at the pop-up list in the software again. Many current, multi-sync displays are using Sony's Trinitron CRTs. That is listed as a setting, as is the Radius PrecisionColor 20" display, although the same CRT is used. If you are unsure as to which setting to use, and your manual doesn't list the CRT type, or look at the back of the display, or call the display manufacturer (have the model number ready), or call Radius Technical Support at 650-404-6400.

Q: I loaded the PrecisionColor Calibrator software, set my phosphor type, adjusted the brightness, and calibrated the display, but the "Save" option is grayed out. What is going on?

A: You have a CPU which wasn't on the market when the calibrator software you're currently using was created, therefore the software can't identify your CPU, and can't save the calibration settings. You need new calibrator software. To get this, call 1-800-544-8456, and ask for part #630-0330. You can also obtain this via modem from most major online services, as well as the Radius Online BBS at 408-541-6190. In the meantime you can still calibrate the display, but you'll have to do it each time you restart. PrecisionColor software 2.2 is current and supports CPUs through, and including the original Power Macintosh series.

Q: When can I calibrate the display, and when is it really necessary?

A: You can calibrate the display whenever you want to. You need to calibrate your display if you've made dramatic changes to the display's brightness and contrast, have changed video cards or moved your existing card to a different slot, have an aging display, or just haven't calibrated in awhile. Once a week is probably just fine, unless color is absolutely critical to your work. If this is the case, daily calibration is preferred. All displays are "aging." Since the life expectancy of most computer displays is between 3 and 5 years, depending on use, 3 years can actually be considered old. Still, CRT's can dim and change much earlier than this, so calibration during the entire life span of a display is recommended.

Q: I thought I calibrated my display last week, and when I just went to calibrate it again, the "settings" option is grayed out. What could be the problem?

A: Your display may not have been calibrated last week. The "settings" option will be grayed out if you went into the settings menu, changed your display profile, and then forgot to calibrate the display.

Q: Is the PrecisionColor Calibrator a "Color Correction Unit?"

A: No. The PrecisionColor Calibrator is a unit designed, and whose sole purpose is, to calibrate computer displays and to maintain that calibration. The calibration involves gamma and temperature control which affect the RGB color appearance of a display, but the calibrator is not designed to match colors for output to a printer, proofer, or other output device. The calibrator is a device to return an existing display to its factory norms, or to set and save gamma and color temperatures to match another display.

Currently, there aren't ANY reliable color-matching systems on the market, short of buying an expensive "closed system," where all of the devices, from the same manufacturer, were made to work in tandem with each other for accurate color output. Still, there are some systems which might help. Kodak and Pantone each have a color matching system on the market. Unfortunately, their systems, like any other, is dependent on "device profiles" provided by other manufacturers. For instance, if your set-up includes a Brand A scanner, a Brand B display, and a Brand C color printer, manufacturers A, B, and C must provide Kodak or Pantone with accurate color profiles of their products. Now, you are dependent on at least four companies to provide you with up-to-date software and profiles so that you can make an attempt at color matching. The calibrator DOES give you the ability to save your display settings as Apple ColorSync and EFI profiles.

Q: What is Gamma, and can I correct for it?

A: Gamma is a curve, actually - or a straight line. "Gamma" is a beginning as far as color input is concerned. Different input devices carry different gammas because they tackle color and computerized input in different ways. A relationship exists between what a computer display is sending to our eyes and the original. "Gamma," is actually the amount of WRONGNESS from the original to the eye because it's specified as the difference of the original (our perception of the original) to the display, (or what we perceive as the image on the display). The amount of that "wrongness" is the gamma. And with gamma comes the term "linearity." If you scan a print into an application, and then hold the print up next to the screen, you'll see a perceptible difference. The difference is the gamma difference. If you adjust the input value of the original print, and the screen brightness and contrast increase accordingly, in direct proportion, you are dealing with linear gamma. Imagine it as a straight line from point A to B. If you adjust the input value of the original print, and the screen brightness and contrast increase somewhat, but NOT in direct proportion, you are still dealing in gamma, but curved gamma - perfect at both ends, but everything between is inexact, growing proportionally more inexact as you get towards the apex of the curve, and proportionally more exact as you leave the apex and head towards the finish. Most of what we perceive as color differences from the original to what we see on our computer screens is in that curved range. And what we see as the largest differences occurs in the apex of that curve - the largest gamma difference. The PrecisionColor calibrator gives you a way of increasing, or decreasing gamma, based on the original gamma of your display, to account for this curve. Standard gamma is 1.8. However, you may want to change the gamma of your display dependent on the source of the image input. A gamma scale is listed in the PrecisionColor Calibrator manual.


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