bkirby@cs.umr.edu (Bill Kirby) (06/19/91)
Thanks for the responses to my x-ray question. I need to clarify my question: I'm not at all concerned with resolution. The images I'm scanning are not bone/tissue, but pictures of a gel made for DNA sequencing (a bunch of little dark lines). I think 200dpi with 64 grey levels would be more than sufficient. My concern is light source. If scanners (and remember I know nothing about scanners :-) have an internal light source, would that interfere with an image that was being lit from behind? Thanks again, +--------------------------+-----------------------------------------------+ | Bill Kirby | Internet: bkirby@cs.umr.edu | | Computer Science Dept. | Bitnet: bkirby%cs.umr.edu@umrvmb.bitnet | | University of MO - Rolla | UUCP: ...!uunet!cs.umr.edu!bkirby | | Rolla, MO 65401 | | +--------------------------+-----------------------------------------------+
wdr@wang.com (William Ricker) (06/25/91)
bkirby@cs.umr.edu (Bill Kirby) writes: >My concern is light source. If scanners (and remember I know nothing >about scanners :-) have an internal light source, would that interfere >with an image that was being lit from behind? Hand-scanners have internal light, at least all I've seen. 1. Some scanners have an adjustable contrast knob (eg Logitech ScanMan 256). twisting this may force it to ignore one source or the other. Try it. 2. The internal light may be sufficient, if you back the transparency with a solid white ground -- eg, oversize white paper. Just because *you* view Xrays on a light-box doesn't mean the scanner is restricted to viewing the Xray negative in that position. This will again call for twisting the contrast knob, as double filtering in grey areas will seriously shift the contrast curve (as I found out photocopying B&W tone transparencies). 3. You could probably disable the light source (you might have to replace it with a resistor, if the software is smart enough to sense a burnt out light and give error). Yet again, you'll use the contrast knob to correctly bias the sensor. I've had some fun with the Logitech ScanMan256(tm) hand scanner with 256-grey scales, although for large tasks I'm sure I'd prefer my firm's power-feed flat-bed scanners. (And I hear we've got some new stuff in the works that blows both kinds away.) I would be careful of one thing: scratching your emulsion with the scanner. I don't know if Xrays have the image on the 'front' or 'back' of the carrier; if the image is on the 'front', you might want to scan through the 'back' and reverse the image in software to protect the emulsion. Alternatively, you could see if the Xray lab has a clear-coat to protect the emulsion -- they may instinctively use it, or only on request; I know Polaroid used to sell such. -- /s/ Bill Ricker wdr@wang.wang.com "The Freedom of the Press belongs to those who own one." *** Warning: This account is not authorized to express opinions. ***
strobl@gmdzi.gmd.de (Wolfgang Strobl) (06/25/91)
wdr@wang.com (William Ricker) writes: >bkirby@cs.umr.edu (Bill Kirby) writes: >>My concern is light source. If scanners (and remember I know nothing >>about scanners :-) have an internal light source, would that interfere >>with an image that was being lit from behind? >Hand-scanners have internal light, at least all I've seen. >1. Some scanners have an adjustable contrast knob (eg Logitech ScanMan 256). > twisting this may force it to ignore one source or the other. Try it. >2. The internal light may be sufficient, if you back the transparency > with a solid white ground -- eg, oversize white paper. Just because > *you* view Xrays on a light-box doesn't mean the scanner is restricted > to viewing the Xray negative in that position. This will again call > for twisting the contrast knob, as double filtering in grey areas will > seriously shift the contrast curve (as I found out photocopying B&W > tone transparencies). I tried this with the Logitech ScanMan 256 I bought last week, with mixed success. The thing I tried to do was to scan 24*36mm b&w negatives for previewing (one of my hobbies is b&w photographing, including all the dark room processing) and for archiving purposes. While putting the negative strip on a white paper and scanning it with contrast set to dark and dpi to 400 works quite well for normal and light negatives, it doesn't work at all for pictures where the interesting details are in the darker parts of the negative. Scanning color negatives didn't work at all. Wolfgang Strobl
rak@crosfield.co.uk (Richard Kirk) (06/25/91)
> The internal light may be sufficient, if you back the transparency > with a solid white ground -- eg, oversize white paper. It all depends on the contrast range on your X-ray. X-ray film can have useful information at densities beyond 6. An 8-bit CCD hand-held scanner with linear A/D will only go up to about 2. A sensible radiographer will adjust the doses and add anti-scatter shielding, but sometimes that cannot be helped when looking at the edge of a cylinder, etc. The usual problem is too little dose. Whether it will work often depends on... What is the biggest density in the region of interest? > Just because > *you* view Xrays on a light-box doesn't mean the scanner is restricted > to viewing the Xray negative in that position. The light goes twice through the film, so the effective density is roughly doubled ( the exposure on high sensitivity film is visibly mottled ). If the original density range was less than 1 then you might get away with it. You will also have a contribution from the backscattered light if you cannot block off the light source. This signal will vary with the smoothness of the film which in turn can depend on the condition of your fixer, and the agitation in your bath. I doubt if it is significant under normal conditions, but beware of reading too much into small structures in the shadows. >I don't know if Xrays have the image on the 'front' or 'back' of the carrier. On all X-ray films I have dealt with there is an emulsion on both sides. This doubles the sensitivity. Under normal viewing conditions the parallax error between front and back will be small. Is this still true with a hand-held scanner? If you have too much contrast on your film for the details to br readable then you can halve the density by bleaching one side of the film with cotton wool and ammonia. A less final method would be to print the image onto a soft paper. If you have the facilities I would recommend scanning a print of an X-ray, if only to establish that scanning the x-ray directly works. I would expect the print to have all the detail in the original with a better contrast range, perhaps a better magnification, and less parallax errors (if significant). If you are trying to get quantitative dose measurements of the film rather than just detect edges there would be an extra round of chemistry to keep constant, but that shouldn't be too hard. Please let us know if it works! -- Richard Kirk Image Processing Dept Crosfield Electronics Ltd. U.K. 0442-230000 x3361/3591 Hemel Hempstead, Herts, HP2 7RH
mussar@bcars53.uucp (G. Mussar) (06/25/91)
In article <4993@gmdzi.gmd.de> strobl@gmdzi.gmd.de (Wolfgang Strobl) writes: >wdr@wang.com (William Ricker) writes: > >>bkirby@cs.umr.edu (Bill Kirby) writes: >>>My concern is light source. If scanners (and remember I know nothing >>>about scanners :-) have an internal light source, would that interfere >>>with an image that was being lit from behind? > >>Hand-scanners have internal light, at least all I've seen. > >>1. Some scanners have an adjustable contrast knob (eg Logitech ScanMan 256). >> twisting this may force it to ignore one source or the other. Try it. > >>2. The internal light may be sufficient, if you back the transparency >> with a solid white ground -- eg, oversize white paper. Just because >> *you* view Xrays on a light-box doesn't mean the scanner is restricted >> to viewing the Xray negative in that position. This will again call >> for twisting the contrast knob, as double filtering in grey areas will >> seriously shift the contrast curve (as I found out photocopying B&W >> tone transparencies). > >I tried this with the Logitech ScanMan 256 I bought last week, with >mixed success. The thing I tried to do was to scan 24*36mm b&w negatives >for previewing (one of my hobbies is b&w photographing, including all >the dark room processing) and for archiving purposes. I've tried scanning slides with my Scanman 256. The white paper trick didn't work, but, back lighting did. It is quite sensitive to the quantity of light (in particular, it is very sensitive to infared). In addition, any kind of florescent lighting causes light and dark bars since they turn off and on 120 times per sec. I found the best way to go was to illuminate a white paper that was place about 1 foot behind the slide and to use a DC powered light. -- ------------------------------------------------------------------------------- Gary Mussar |Internet: mussar@bnr.ca | Phone: (613) 763-4937 BNR Ltd. | | FAX: (613) 763-2626