jim@baroque.Stanford.EDU (unknown) (11/28/89)
Most desktop scanners are very low resolution. There are some newer devices which use a camera to capture an image off of a 35mm slide, but I doubt that they can give 256 to 1024 gray levels and certainly not 2048x2048 pixels at a single go. The only device I know of which meets your needs is a scanning microdensitometer which digitizes a negative by moving it around in front of a focused light source with the transmission measured by a PMT tube. Filters can be used for scanning color negatives. Different aperature shapes and sizes are used to control the resolution and pixel shape. I don't know what the overall price range is, but ours, granite slabs, computer interface and all cost around $200K a few years ago when we bought it from a company now owned by Perkin-Elmer. These beasts can produce 12bit images of almost arbitrary resolution Jim Helman Department of Applied Physics P.O. Box 10494 Stanford University Stanford, CA 94309 (jim@thrush.stanford.edu) (415) 723-4940
rodney@sun.ipl.rpi.edu (Rodney Peck II) (11/28/89)
>>>>> On 27 Nov 89 21:47:51 GMT, jim@baroque.Stanford.EDU (unknown) said:
jim> Most desktop scanners are very low resolution. There are some newer
jim> devices which use a camera to capture an image off of a 35mm slide,
jim> but I doubt that they can give 256 to 1024 gray levels and certainly not
jim> 2048x2048 pixels at a single go.
jim> The only device I know of which meets your needs is a scanning
jim> microdensitometer which digitizes a negative by moving it around in
jim> front of a focused light source with the transmission measured by a
jim> PMT tube. Filters can be used for scanning color negatives.
jim> Different aperature shapes and sizes are used to control the
jim> resolution and pixel shape.
jim> I don't know what the overall price range is, but ours, granite slabs,
jim> computer interface and all cost around $200K a few years ago when we
jim> bought it from a company now owned by Perkin-Elmer. These beasts can
jim> produce 12bit images of almost arbitrary resolution
We just bought a slide scanner from microtex (I think) which does 4096x4096
in 24 bit color (that's 8 per rgb channel) for $8,000. It will of course,
do 4096x4096 by 256 level gray as well.
It's not fast, but high res scanners never are.
Send me mail and I'll see what sort of information I can find. $200K is
far too much money to pay for grayscale digitizing these days.
--
Rodneyiony@olsen.UUCP (Ion Yadigaroglu) (11/29/89)
This discussion brings to mind a project I've had for some time
(not in any way started). I was thinking of modifying a CD player
to make a microdensitometer. You would put the (small) strip
of film on a disk with a big hole cut out. Advantage would be
of course that you could re-use most of the CD player, including
laser, lens, motor, speed-controling circuit, stepper motor
for laser, and maybe even the feedback tracking circuit (to
position the laser). The only hardware missing is a good
intensity cell on the other side with its A/D converter.
Problems are obvious though: difficulty in playing around with
mass produced electronics, synchronizing all the different
signals, taking care of curved pixels, etc.
Anybody like the idea?
Iondave@imax.com (Dave Martindale) (11/29/89)
Both Nikon and Eikonix sell packaged scanners specifically designed for digitizing 35mm slides. The Nikon does about 6000x4000 pixels, while the Eikonix is 4000x2666 roughly. I know the Nikon is 8 bits/component (24 bits/pixel) and the Eikonix is at least 8 too. The Eikonix uses a linear CCD sensor array, moving either the slide or the sensor array mechanically to get scanning in the other direction. The Nikon moves the slide, although I've been told that Nikon has another model that holds the slide still and moves the sensor instead. If you need better intensity resolution than 8 bits, Eikonix also makes a 12-bit/component scanner with 4096x4096 pixels called the 1412. This one isn't specifically designed for slides, but can be used for that. I believe the Nikon box is around $10K; don't know about the Eikonix. The results with either won't be as good as a scanning microdensitometer, but they're a lot cheaper.
dave@imax.com (Dave Martindale) (12/01/89)
In article <126@tobler.UUCP> iony@tobler.UUCP (Ion Yadigaroglu) writes: > > This discussion brings to mind a project I've had for some time > (not in any way started). I was thinking of modifying a CD player > to make a microdensitometer. You would put the (small) strip > of film on a disk with a big hole cut out. Advantage would be > of course that you could re-use most of the CD player, including > laser, lens, motor, speed-controling circuit, stepper motor > for laser, and maybe even the feedback tracking circuit (to > position the laser). The only hardware missing is a good > intensity cell on the other side with its A/D converter. Well, it's not this simple. A CD player has a 2-axis positioning system (tracking and focus) that is specially designed to follow a spiral pattern of pits on a disc. All of the signals that drive the focus and tracking servos come from that spiral track of data. If you replace the very specific pattern of the CD data surface with an arbitrary piece of film, these servo circuits could not function. You'd have to replace the focus and tracking circuitry with something that can do high-accuracy positioning using its own references, instead of following a pre-written pattern. You could use a laser interferometer or similar system to provide the position feedback for the laser head. But it would likely be far cheaper to scrap the entire CD positioning system and use precision mechanical screws instead. The laser block out of a discarded CD player might be useful though.
iony@olsen.UUCP (Ion Yadigaroglu) (12/06/89)
>> This discussion brings to mind a project I've had for some time >> (not in any way started). I was thinking of modifying a CD player >> to make a microdensitometer. (...) > >Well, it's not this simple. A CD player has a 2-axis positioning >system (tracking and focus) that is specially designed to follow >a spiral pattern of pits on a disc. All of the signals that >drive the focus and tracking servos come from that spiral track >of data. > The idea is to keep the disk with its tracking info. While the laser is over the film, you freeze the positioning and focus system. Of course you have a little less time for doing both, but it seems to me the feedback system might be flexible enough to handle this. The biggest problem is avoiding that the circuits "panic" as they are designed to handle only small breaks. Thanx for the comments, Ion
dave@imax.com (Dave Martindale) (12/07/89)
In article <129@tobler.UUCP> iony@tobler.UUCP (Ion Yadigaroglu) writes: > >The idea is to keep the disk with its tracking info. While the laser >is over the film, you freeze the positioning and focus system. >Of course you have a little less time for doing both, but it seems >to me the feedback system might be flexible enough to handle this. >The biggest problem is avoiding that the circuits "panic" as they >are designed to handle only small breaks. The servo loop probably has a low-pass filter between the error amplifier and the motor driver. A few judiciously-placed FET switches and maybe an extra opamp to act as a buffer would allow you to "freeze" the servo drive for reasonable times. However, locking the drive current at some particular current is no guarantee that the pickup will remain motionless. In fact, if it was moving at the time you went into "freeze" mode, it is guaranteed to keep moving for a while. And then there is the disc itself. Watch the servo circuits in a CD player sometime - they are constantly making small adjustments in focus and tracking because your average CD is not flat, and does not have its "centre" hole punched in the centre. The player NEEDS those servo loops operating all the time just to stay on track. If you "froze" the pickup for any significant distance, it is just about guaranteed to be out of focus and out of alignment when the spiral tracks re-appear. If you only want to scan images the size of 8mm film frames, you might just get away with it. But I doubt anything larger could work.
kevin@ucrmath.UCR.EDU (kevin lund) (12/08/89)
In article <1989Dec7.134309.11032@imax.com> dave@imax.com (Dave Martindale) writes: [...] > >And then there is the disc itself. Watch the servo circuits in a CD >player sometime - they are constantly making small adjustments in focus >and tracking because your average CD is not flat, and does not have its >"centre" hole punched in the centre. The player NEEDS those servo >loops operating all the time just to stay on track. If you "froze" the >pickup for any significant distance, it is just about guaranteed to be >out of focus and out of alignment when the spiral tracks re-appear. >If you only want to scan images the size of 8mm film frames, you might >just get away with it. But I doubt anything larger could work. How about slaving a second head positioning mechanism to the servo circuits of one with a real, no film taped on it CD? Then you could do anything you wanted on the other one - have a nice white, grooveless background and your picture could be as big as the CD. Or bigger if you want; just use videodiscs instead. Of course, I believe the original intent was to come up with a cheap scanner and this is getting a bit expensive...