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Input/Output/Workflow Scanning, printing, color management, and discussing best practices for control and repeatability

Finding a scanner's "sweet spot"

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  #11  
Old 06-13-2002, 02:24 PM
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jeaniesa jeaniesa is offline
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Hmmm - given that you just posted a question about Linux drivers for a Scitex, I think that perhaps you DO have a high-end scanner!
Jeanie
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  #12  
Old 06-13-2002, 02:38 PM
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Since the flatbed scanner sensors that read the top of a page are the exact same sensors that read the bottom, I wonder why scanners have a 'sweet spot'?
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  #13  
Old 06-13-2002, 03:39 PM
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lack of equal quality throughout in the glass??
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  #14  
Old 06-13-2002, 04:36 PM
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G. Couch G. Couch is offline
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Quote:
Originally posted by Doug Nelson
Since the flatbed scanner sensors that read the top of a page are the exact same sensors that read the bottom, I wonder why scanners have a 'sweet spot'?
Good question! I have heard several people talk about scanners having a "sweet spot", but no one ever really explained why. None of the seb sites I found mentioned much more than "scanner inconsistencies". I guess lower end CCDs tend to degrade a bit toward the edges? I'll see if I can track down some more info.
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  #15  
Old 06-14-2002, 02:44 AM
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Quote:
Since the flatbed scanner sensors that read the top of a page are the exact same sensors that read the bottom, I wonder why scanners have a 'sweet spot'?
Light intensity decays as a 1/r^2 function (where r is the distance between the source and the detector), so it is easy to see that any irregularities or uneveness in the track that the source/detectors follow can have a marked effect on the amount of light reaching the detectors.

This can be clearly seen in the dark backgrounds of some of the pics in the "Scanning Objects" thread.
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  #16  
Old 06-14-2002, 03:32 AM
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Quote:
Originally posted by jeaniesa
Hmmm - given that you just posted a question about Linux drivers for a Scitex, I think that perhaps you DO have a high-end scanner!
Jeanie
My flatbed scanner is a Heidelberg/Linotype Hell Jade. Ok, ppl see this as a high-end scanner, but this is actually the cheapest, most basic one they have (600x1200dpi, 24bits SCSI). That's why I was interested to try this 'sweet spot' thing. I thought some parts of the scanner gave better results than others and thought this was a good way to check it...
Got it secondhand for $200 including transparency adapter. (At the dutch equivalent of E-bay).

As for the Scitex, I swapped it for a used Nikon F4 and lens

Hmm...anyone here who wants to swap a Sony 24" TFT screen for a 1986 Honda Civic? Only 128.000km !!
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  #17  
Old 06-14-2002, 06:03 AM
Stephen M Stephen M is offline
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As noted, different substrates may show different levels when equalized. Perhaps try different types of white paper, as well as black. Matte or less glossy may work better.

Two good links on consumer scanning can be found here:

http://digitaldog.net/files/Scanningtutorial.pdf

http://www.thelawlers.com/FTP/B&W%20Scanning.pdf.sit

The fine detail test suggested by Andrew Rodney using currency is a good approach too (legalities though). GAFT and other print based organisations would have dedicated scanning targets, for both colour/tone and detail.

A Umax 'prepress' scanner I used to use had a 'zero' point marked on the ruler at the front of the scanner - this spot was where the manual suggested the best focus was obtained, tests also showed this...so tranny scanning was done one at a time, while reflective was done with more originals and batching so that more productivity could be gained.

This sweet spot issue can be critical when you are attempting to batch scan many originals. Some scanners let you set separate scan crop frames and apply separate endpoints/gradation etc to each scan frame and save the files off to disk or live to Photoshop for post processing. This is a huge productivity bonus, but if the flatbed has serious probems over the entire scanning area - quality may be sacrificed or the batch may be smaller than you would like if you try to stay within the better area.

I used to use a CreoScitex EverSmart Supreme high end flatbed (US40K) - which had patented XY positioning...the scanner head moved both vertically and horizontally to focus in on parts of each image, then it would stich the strips into one final scan. Sounds scary, but I never saw any issues from this technique. With this line of scanners you can use the full surface of the bed and the biggest plus is the batch scanning workflow. Prescan the whole bed, set your scan crops, adjust your first scan and then send to the scan qeue, adjust the next prescan crop while the first is scanning/writing to disk etc.

I currently work for a publisher who uses a drum - I am not sure that a high end flatbed could match the pace/productivity of a good drum and operator.

Now I just use a humble Microtek flatbed and SilverFast software - since the drum does most of the work (I am not a drum operator and scanning is not the focus of my job).

Scanning is such a deep area to go into - and any discussion involving scanning should include this link:

http://www.scantips.com

Have fun.

Sincerely,

Stephen Marsh.
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  #18  
Old 06-14-2002, 02:17 PM
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I think BigAL is on the right track with his explanation. I did some more research and found this in one of my books, Scanning the Professional Way-

"The fluorescent lamps used in most flatbed scanners are susceptible to fall-off, a phenomenon that produces better illumination near the center and less at the outer edges of an original."

Obviously higher end devices have better light sources, higher quality CCDs, A/D converters, etc... I think electronic noise plays a part as well. Certain areas in the scanner are more susceptible than other areas to interference.
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  #19  
Old 02-04-2005, 11:35 AM
WideAngle WideAngle is offline
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Sweet Spot

I am using a Microtek 6100pro with silverfast which I guess is sort of midrange (about 400CAN dollars). see the pic for the sweet spot after applying equalization, I assume an even gray is good? There is some noise on the edges though.
Wide angle
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  #20  
Old 02-04-2005, 04:13 PM
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Posted below are before and after shots of my Epson 3170. The first was by laying a sheet of heavyweight matte paper and hitting the button. The second was augmented by pressing down on the lid while scanning, as I noticed the first time that the dark spot was caused by a slight warp in the paper. I thought the difference was remarkable.
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