cory@three.MV.COM (Cory Kempf) (06/07/90)
news@genrad.UUCP (Network News) writes: >that could also support PC's.) We need reasonably high resolution - >256 gray scale - but will be printing on a laserprinter rather than >a type setter. >From: dmm@genrad.com (Dottie MacKeen) >Path: dmm >We want both graphic scanning and the ability to add software to add >OCR. Most scanners (all, I think) can interface with software for OCR. >We are considering a system from Microtek that offers both gray scale >and color. I would appreciate any feedback that scanner users have on >the function in general and on specific scanners and software. Well, I can't comment on Microtek's product, having never used it. >The articles I have read sound as if attempting color scanning is >best left to graphic professionals since a great deal of expertise appears >to be required. Colour scanning is simple: Put the original in the scanner, do the same selections that you normally would, and it scans. Here is where the hard part comes in: Colour, or Which shade of Red is Red? The problem is real bad: (most) scanner manufacturers do not calibrate the colour on their scanners, most monitor manufacturers don't calibrate the colour on their monitors, and most printer manufacturers don't calibrate their inks. Add to that the fact that the scanner sees reflected colour, so the colour that it sees is dependant on its lamps/filters, as well as the original. The colour that the monitor displays is direct, so that eliminates one problem area (sort of). The colour that you see on hard copy is also reflected -- which means it is dependant on the lighting. There is a concept called metamerism: two colours look the same under one light source look different under a different light source (or why else do you think that paint stores have those funky booths with the multiple light sources?). And, just to make matters even more fun, the scanner can see one range of colours, the monitor can display a different set, and a printer can print out a third. In most cases, they do partially overlap, but the monitor can do much more than the printer. As if that was not enough, scanners and monitors think of colour as Additive: this much red, green, blue (RGB space). Printers use Subtractive (Cyan, Magenta, Yellow, Black -- CMYK space). Remember back in grade school when you were told that Blue and Yellow made green? and that Red and Blue made Purple? Well, they lied. Sort of. Think of Cyan as a absorbing Red light, Magenta as absorbing green light, and yellow as absorbing blue light. Since white light is made up of everything, you need to take out the red and the green to get blue (Trust me). Theoretically, if you take out the red and the green and the blue, you will get black. Unfortunately, the CM&Y inks are not (usually) that well ballanced, so they through in black to fix it. If you have waded through all of that, you have just scratched the surface of colour theory. Anyway, that is why colour scanning is so difficult -- trying to match the colours. > Additionally color scan images appear to take enormous >amounts of disk - one scanner at full resolution was said to create a 75 meg >file. sounds a bit high... should be closer to 50MB... assuming that you are doing 300 dpi, 11*17, 8 bits / dot / colour (24 bit colour). BTW, in 9 out of 10 cases, scanning at 300 dpi colour or greyscale is a waste of time... you are only getting about 60 dpi (effective) out of your printer. >Does anyone have any color scanning experience? Yes. +C -- Cory Kempf I do speak for the company (sometimes). Three Letter Company 603 883 2474 email: cory@three.mv.com, harvard!zinn!three!cory