[Digital BW] Re: (Paul)Why do mac and pc use different curves?
2002-03-15 by Paul Roark
Jim, You wrote: >...Why would a >Spectrophotometer be better than a densitometer to tweak your curves >when reading a test step wedge directly off a printer? As best I can tell, "densitometer" is just the unofficial term used for what the manufacturers call "spectrophotometers." I make the assumption that these devices are better at reading color and density -- their reasons for being -- than the affordable desktop scanner I and I think most of us use. What I actually find is that the densitometer allows me to calibrate my Epson 1600 scanner gamma. This is not a trivial problem. And, I think that one thing that might real help is if I make calibrated test strips available to those I work with who are doing scanning of test strips. Once the gamma is set, the scanner then makes a good way to quickly read the grayscale densities and have the results in percentages. However, my scanner's color readings are off and not very linear, according to the X-rite. And, judging from what I saw in the many scans from others, there is quite a bit of variance among scanners. So, I'm now using the densitometer to read the colors, which was most important to get a really neutral curve with the VM-sepia. Actually, I'm now balancing out the old 3000-PC "cold" curve to be a sepia "brown" curve (one step back from full-on sepia -- maybe I ought to call it "very warm"). I'm finding that visual eyeballing of the test strip is as good as anything for the color of this curve. >I have a friend who has a computerized way of generating curve data, >but uses a densitometer. I was arguing that it might not get all the >color tones right, esp with VM.? I don't know. There are expensive spectrophotometers/densitometers that do automate the reading, at least. However, they are big bucks. (A DPT22 like I have has recently sold on EBay for about $300.) Paul