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Join Date: May 2008
Location: San Francisco - East Bay area
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It's even more complicated than that. To calibrate a printer correctly, you need a reflectance meter that has a built-in reference light source (that also needs periodic re-calibration). The best types of these are made so that you insert the paper so the read head is over the area of the page you want to measure. You typically then move a lever that lowers the read head onto the paper and the reading is made.
BUT... that's only the beginning. The paper you use will affect the calibration significantly. If you want really consistent results, you'd want to re-calibrate for each new batch of paper. And... if you insert the paper in different orientations (4 possible ways... "notmal", rotated 180 degrees, or bottom up vs top up), you'll get 4 different measurements because the way the ink hits the grain of the paper will change the measurement results. Also, if you use photo paper vs plain paper, calibration results will be very different. And lastly... any time you change an ink cartridge, the measured results will change so recalibration may be needed. It's nearly impossible to calibrate color laser printers that use powdered toner. Ink jet printers are more calibrate-able but the paper variable is fairly significant. If you use Deluxe Photo Paper for 2 years and the manufacturer changes to Ultra Deluxe Photo paper and stops making the old Deluxe paper, your calibration results will change. I used to work on systems that used dye transfer printers because each roll of dye (8.5x11 inch panels of cyan, yellow, magenta, and black dye on something similar to Saran Wrap) could be characterized and the end user could input the correction factor values without having to recalibrate the entire system. You don't get that sort of data with consumer-grade printers and ink, so you end up having to keep recalibrating whenever there's a variable inserted into the printing process.
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