View Full Version : DIY Drum Scanner?
mongole
27-Feb-2018, 16:26
Hi,
since some years, the DiY DSLR scanner project is popping in my mind again and again, but actually never headed of to start it. I really like the idea, I can imagine I like the handling. I am a bit concerned regarding the sharpness / DOF thing and mainly to get a good light source to scan color sheets / negatives.
During reading another post regarding the v850 scan quality (again thinking about buying one...), somebody mentioned advantages of drum scanners again... Sure, old, used, nobody knows how long you get spare parts. List goes on and on. No option for me. Definitely.
Then it struck me. Is it possible to build a drum scanner on your own as open source project?
What do you need:
A rotating glass tube of good optical quality (expensive for sure).
three photomultiplyers
a light source (in the center of the tube?)
a photomultiplier moveable along the center axis of the glass tube
electronics to read out the stream of the data from the photomultiplier
software to display the data and control the whole thing
For sure, this a completely naive view of the whole project. I have no idea where one could get a glass tube of needed quality and the price point the same goes for the photomultiplier... Nether have I used a drum scanner, nor do I know exactly how one works...
As I am software developer and have some experience with tinkering around, I could cover this parts of the project. ;)
Does anybody here know enough about the technical details about the glass tube, the photomultiplier and electronic side of the story to decide whether this whole idea is crazy or feasible?
interneg
27-Feb-2018, 17:04
Hi,
since some years, the DiY DSLR scanner project is popping in my mind again and again, but actually never headed of to start it. I really like the idea, I can imagine I like the handling. I am a bit concerned regarding the sharpness / DOF thing and mainly to get a good light source to scan color sheets / negatives.
During reading another post regarding the v850 scan quality (again thinking about buying one...), somebody mentioned advantages of drum scanners again... Sure, old, used, nobody knows how long you get spare parts. List goes on and on. No option for me. Definitely.
Then it struck me. Is it possible to build a drum scanner on your own as open source project?
What do you need:
A rotating glass tube of good optical quality (expensive for sure).
three photomultiplyers
a light source (in the center of the tube?)
a photomultiplier moveable along the center axis of the glass tube
electronics to read out the stream of the data from the photomultiplier
software to display the data and control the whole thing
For sure, this a completely naive view of the whole project. I have no idea where one could get a glass tube of needed quality and the price point the same goes for the photomultiplier... Nether have I used a drum scanner, nor do I know exactly how one works...
As I am software developer and have some experience with tinkering around, I could cover this parts of the project. ;)
Does anybody here know enough about the technical details about the glass tube, the photomultiplier and electronic side of the story to decide whether this whole idea is crazy or feasible?
The most difficult bit is the software - how to correctly reassemble the sampled data across (potentially) multiple simultaneous files while preventing errors & resolving questions of how many 'samples' are taken & averaged for every pixel in the final file - all at a rate of several thousand samples per inch. The rest is basically some fairly high precision mechanical, optical & electronic engineering. You'd need access to some pretty serious machine tools to do it right. We're talking about spinning a thick wall perspex drum at up to quite high RPM's with repeatable precision. Power supplies should be as standardised as possible. Pretty much any computer today will run rings round any onboard hardware they used in the 90s to try & speed things along - add a thunderbolt or USB-C after the Analogue-Digital-Conversion stage & you'd have something much more future resistant.
Bruce Watson
27-Feb-2018, 19:47
Does anybody here know enough about the technical details about the glass tube, the photomultiplier and electronic side of the story to decide whether this whole idea is crazy or feasible?
It's acrylic, not glass. And the whole idea is completely crazy, but of course it's feasible. Somebody did it in the first place, no reason you can't do it over again now.
An accomplished mechanical engineer would be a big help. Without one I doubt you can make a functional drum scanner.
The name of the game is accuracy and precision (these are not interchangeable concepts). That is, you have to read each pixel in real-time as they pass in front of the light beam going through the drum, the film, and the overlay to the PMTs. Each pixel has to be read by each of the PMTs, passed through the log amps to the A2Ds, and the digits have to make it into the file, all in real-time as the drum turns. The drum has to index to the next line (that is, it has to move *and* settle) in the time it takes for the drum to make the partial turn from the end of the film back around to the start of the film. There's no going back, no do-overs, no repeat scans. One and done. Each and every pixel. Thousands of pixels each turn of the drum. Just as fast as the drum can turn.
Really, the amount of money you'd spend on just the mechanics would be 10x what you can buy a used drum scanner for. Then at least you have all the mechanical parts. If you want to redesign all the circuits and the software, have at it. But it's probably at least a couple of orders of magnitude more difficult than you seem to think.
First thing you do is, make a formal functional specification for it. If you can't do that, you can't make a drum scanner. You can't solve a problem that you can't define.
All that said, I think a modern drum scanner would be a pretty interesting thing to do. It would be especially interesting to replace the light source with an LED. My drum scanner uses xenon bulbs, very expensive, very bright (I have no idea how many lumens), and very hot, but a beautiful clean/clear balanced white light. But I would imagine one could do just about the same thing with an LED these days, if one can manage the flicker.
Better yet, why not use a laser, or three. RGB lasers directed to converge at the pixel (spot on the film you want to measure) and then diverge to three PMTs. This could get interesting...
Bruce covered most everything I can think off but I'll add that another complexity would be the fine precision that they require for everything. The drum spins at ridiculously fast speed on my Scanmate and Tango and the focusing system has to be microscopically precise. If you really want a drum scanner today, there is nothing better than getting one from Karl Hudson (http://hudsongrafik.com/) and letting him take care of it for you. You can alternatively get one from Michael (http://www.scansolutionsonline.com/) if you are in the market for a table-top drum scanner or a high-end flatbed that is near drum scanner quality. IMO, both options will cost you significantly less than trying to make one from scratch.
Pali
You can't solve a problem that you can't define.
What an awesomely pragmatic approach. Bravo !!
Great project though to sink one's teeth in ...
barnacle
28-Feb-2018, 14:56
Oddly enough, I was thinking about the very subject only this month (something to distract me from the day job)... and it occurred to me that the critical point of a drum scanner is, basically, an arbitrarily small spot of very bright light and a single (I was thinking monochrome as a first step) sensor. It doesn't actually need a drum(!) since as far as I can see the purpose of the drum is to generate a raster.
The rotation provides a scan in one axis by spinning, and a scan in the other by either the light source or the drum moving axially, perhaps on a screw as the drum scans?
(I've never seen a drum scanner; this is extrapolation based on descriptions I've read and good knowledge of broadcast technology.)
One could replicate both the scan axes with a flat image and a stepper system, as in a standard flatbed scanner. The pixel count would be set by the minimum step size.
A laser LED and focussing lens could be arranged to produce a variable spot size; the sensor needs only to be large enough to accept the largest spot. Timing for the ADC is not critical since the spot doesn't move until the ADC is complete - though there may be a time limit on how much energy is transferred to the film by the laser. It would be a shame to set fire to your image!
The software is not that complex (but then, that's the sort of stuff I do in the day job). The data appears one sample per pixel, just dump it into a file in real time. Post process the file if desired. I'd probably aim for a 16-bit sample and adjust the brightness of the LED to give as close to a full-scale sample across the image as possible.
I'd probably arrange things so that the laser and sensor stay put, and the film moves on a platten, but it could be done the other way around.
Just ideas...
Neil
There is probably CNC stepper/sensor accessories for controlling generic lathes that could operate the mechanical aspects of a diy drum scanner. Probably a lathe could be the basic of the mechanics. The hardware for controlling those is not going to go away; it will probably get more interesting. I'd have a index mark parallel to the film that started the recording for each row. I don't use a drum scanner but I would certainly at least inspect a broken one before proceeding to build one as it's probably full of clever tricks you won't want to reinvent. If the film were rotated the same amount as the pitch of the lead screw, it would never have to stop feeding and could turn slowly and continuously while scanning if the sensor were in place of the tool post/turret.
Honestly, I'm pleased with my epson flatbed for LF. Something better for MF would be nice though if it were as convenient.
Yes, it's crazy! I realized in meantime as well. If you want to have a somehow future proof solution, buying a drum scanner and rebuild the electronics and write the software would be the way to go.
Though I have no idea how much a photomultiplier costs, up to now and where to get it.
This page showed me how a drum scanner is build: http://www.terrapinphoto.com/drumscansaga/
Also this thread gave some real valuable information: https://www.rangefinderforum.com/forums/showthread.php?t=134187
What I do not understand up to now is: Why needs the drum rotate that fast? Is it out of rpm consistency? The faster it rotates, the less the rpm fluctuates?
Is it really necessary to read the data in a constant stream, if the AD conversion is not fast enough? Would it not be enough to measure the time of one rotation, take the desired resolution per perimeter, divide by let's say 10 and sample every 10th pixel in the first round. Then shift one pixel and sample every 10th+1 pixel and so on. You get the idea. I guess it's not as accurate as do it in one stream.
But I don't think you need to reposition the light in the gap where there is no slide. Just move on one step and wait some rotations. Would be beneficial to reduce vibrations due to reposition anyway...
I am a bit amused Neil, you as software develope also do not seem to see it as undoable. Maybe it's a trait of software developers (as I am one myself) to be ignorant enough in the other technical fields to even think about to try it! ;) :D
Let's see where this will lead. If it even will lead to somewhere.
Thanks for all your valuable input!
Greets,
Andreas
Bruce Watson
2-Mar-2018, 09:43
What I do not understand up to now is: Why needs the drum rotate that fast? Is it out of rpm consistency? The faster it rotates, the less the rpm fluctuates?
At 600 rpm, my scanner takes an hour+ to scan a 5x4 sheet of film at around 11x enlargement. IIRC (and it's been years so I might not remember correctly) it was something less than 4000 dpi. Slower rpms mean longer scan times. How long are you willing to take?
BTW, this is what I mean by writing a formal functional specification. Specify what you are trying to do before you try to decide how to do it.
Is it really necessary to read the data in a constant stream, if the AD conversion is not fast enough?
If you want to complete the scan in a reasonable amount of time, then yes, it really is necessary. But it's a meaningless question. If they could already do this in 1996, why couldn't you do it now? I guarantee that today's tech is faster than 1996 tech.
barnacle
2-Mar-2018, 13:47
I am a bit amused Neil, you as software develope also do not seem to see it as undoable. Maybe it's a trait of software developers (as I am one myself) to be ignorant enough in the other technical fields to even think about to try it! ;) :D
Greets,
Andreas
Call me a generalist, Andreas; I'm a software developer working on the bare metal for domestic products - but I also develop the hardware and previously developed deep-drilling robots for bore-hole guidance and logging working five kilometres underground... and before that, I worked as a broadcast engineer (at many levels) in the BBC for over thirty years.
Photomultiplier tubes are available cheaply - under thirty pounds - second hand parts on eBay; you can probably pick up a high voltage supply at the same time - but the design of such isn't difficult. But as I said in my post, I think that current optical sensors are probably good enough to use directly. The trick is to get the sensor biased correctly to ensure as large and as linear an output as possible between solid silver and clear film base. Everything after that you can do in software. And since you control the speed of the scan, you also control the speed at which data need be output and stored.
At a first thought, in order of difficulty:
- analog design for a clean signal of sufficient resolution and dmax, and a suitable DAC
- mounting and moving the image
- handling, processing, and storing the data
Neil
Hi all!
First things first: Neil, I really hope I did not offend you. This had been the last of my intentions. As English is not my mother tongue, I might sound a bit harsh from time to time. It's a really impressive list of different areas you have covered during the years!
My experience up to now, is mainly Java web and desktop application development and some years with JavaScript now. Currently I am interested to learn some Go, as it would be great for multi-core CPU programming. For sure I did a bit of C++ years ago, but whenever I get in touch with it I realize how handicapped I feel with this language...
Regarding mechanical stuff, I also did service my motorbikes on my own. The precision part of the mechanics for sure is done by other engineers, just assembling. But enough to know, how to deal with this parts.
And long time ago, I went into a school for electrical engineering. But I never worked in this area. Hence, there are some hazy memories about electrical stuff, but it's all covered below a big layer of dust.
In the moment I would say, I could imagine to take an existing drum scanner and replace the electronically part. But only with a long and steep (re)learning curve.
I can imagine to pursue such kind of project as a real long term thing. Just to invest some hours here and there. Hence, for sure it would take more than some months to see something polished working in the end.
After starting this thread, I stumbled upon two ScanMate 5000 scanners. Not to far away of my home town. I took a look on them on Sunday and consider to buy both of them. One is broken, but the current owner thinks it should work, after fixing some damage done during transport. The second one is in working condition. I could use one to scan for now, have the second for spare parts and also as base for the DIY scanner project. We the working one (preview, focus and white point calibration), but could not do any scans, as the software lacks a dongle and we could not figure out how to get into demo mode. Next Sunday I will know more, as I bring my own old computer with SCSI connector to test...
Then I wanted to cover the points discussed up to now:
Bruce, for sure you are right! "First thing you do is, make a formal functional specification for it. If you can't do that, you can't make a drum scanner. You can't solve a problem that you can't define."
But first, one has to get a to a state of knowledge, one can define the formal functional specifications.
And of course, you are right. The whole thing is much more complex and complicated as I expected it in the first moment. Maybe it stays a thought experiment, but I like to play around with things like that.
Scan and rotational speed. Optical header positioning.
Of course it has to rotate as fast as e.g. 1600 rpms. If one scans a 8x10 inch sheet, you have 10 * 5000 (dpi) horizontal resolution. Divide by 1600 rpms/lines it's 31.25 minutes to do the scan. Actually straight forward, as soon as you do the simple maths. And for sure it also has to be positioned on every rotation in the gap to archive this scan speed.
Mounting / moving options.
I think rotational is the way to go, as moving linear in two directions would be slow and take long time. You would have to accelerate the table (?) and stop it again. This is for sure much slower than to rotate at constant speed and reposition for one pixel on every turn. Of course it would be easier to handle, but would produce scanning times of hours. I also think todays general use ADCs should be capable to take enough samples fast enough. But would have to checked of course.
light source:
LED would allow to skip the optical fiber to illuminate the sheet, but I guess to shape the light correctly, it would also increase the effort. The optical fibers give the light already a direction... not very scientifically, but I think you know what I mean.
Laser as light source. Would this mean to skip the optics to bundle the light into a focus point? I have far to little knowledge about laser light, to grasp the implications. Would the same photomultipliers be able to detect them?
jp, actually a drum scanner is some kind of lathe! just a very special kind of! ;)
Luckily the taking of the image information is non destructive in this case! :)
Neil, you mentioned alternative sensors. What kind of them did you think of? Do you have examples?
Pali, precision for sure would be the most challenging part on the whole project. But starting with an existing scanner could be the key to avoid it for the beginning. After a prototype is there, one could replace existing parts with own designed ones. If this ever happens... :)
One point popped up my mind: color profiling!
Of course would have to be done with targets and software.
(Just a note for later: drum material perspex)
Well, this beast is really going to be complex. A one persons lifetime project! :D
I am interested to hear your opinions about this wrap up!
Greets,
Andreas
Just in case you are interested, the service manual for the ScanMate 5000: http://www.analogfilm.camera/wp-content/uploads/2017/02/Scanmate-SM4000-5000-Service-Guide.pdf
It has some valuable information about the schematics of the thing...
Peter De Smidt
5-Mar-2018, 08:50
Maybe buy a cheap drum scanner, perhaps one that needs repair, and totally rebuild it. That would probably give a lot of info for coming up with your own design.
Maybe buy a cheap drum scanner, perhaps one that needs repair, and totally rebuild it. That would probably give a lot of info for coming up with your own design.
Well, for the mechanical part of the story for sure.
From the electronically side, I just did some calculations...
Following the service manual, the ScanMate scans at 5000dpi with 900 rpms. Which are 15 rounds per second.
As the drum has a diameter of 100mm and is 314 mm long (sounds a bit like pi, doesn't it?) the extend is (surprise surprise) 314,12 mm (sounds like pi again) and the whole area of the drum gives a square.
Google tells me this are 12,3622 inches.
This means an extend has 12,3622 x 5000 pixels = 61.811 pixel. This are a lot of pixels!
If we scan now with 15 rounds per seconds our roughly 62.000 pixel we get (15 x 62.000) 930.000 sampels per second. Also known as Hz.
This means the AD converter has to be capable of about 1 MHz.
Obviously this is something which can be achived with this chip (http://www.ti.com/product/ADS8329/description) which costs around 15 Euros...
barnacle
5-Mar-2018, 13:29
Andreas, no offence understood or taken!
Light sensors include:
- photo resistors, where the resistance changes depending on the light falling on it. Pros - cheap. Cons - neither fast nor sensitive, probably very non-linear. Very thermally sensitive.
- photo diodes, where the voltage generated across the diode changes according to the light. Pros - cheap, very fast, reasonably linear, reasonably sensitive. Cons - high output impedance
- photo transistors, a photodiode formed in the base-emitter junction of a bipolar transistor. Pros - cheap, fast, sensitive. Cons - non-linear, maybe restricted range.
- ccd and cmos sensors, usually either a one or two dimensional array of sensors; charge is generated by the action of light in a diode junction and shifted out in bulk. Pros - reasonably cheap, small cell size, usually with amplification and linearisation on chip. Cons - physical sensor arrangement not really suited to the shape of the spot we need to detect, non-matched between cells, complex driving electronics.
- photomultiplier tube, where an avalanche of electrons is generated from an initial photo-electric generated charge. Pros - very sensitive, large target area, good output level. Cons - high voltage supplies, expensive.
Bearing in mind that the idea of a drum scanner is to (effectively) move a very small spot across an image, there are a couple of issues, even ignoring the mechanics of the movement, and the issue of actually generating the small spot. We want a large exposure range with at least 14 bits of image depth and we need to be able to discriminate between very similar values at both dark and light levels. Ideally, we'd prefer to limit the amount of light we get on the film to avoid it catching fire...
The PMT is probably the best option in terms of its dark performance - it can detect single photons - but a photodiode or transistor is certainly something I'd like to play with as a first attempt.
Neil
Bruce Watson
5-Mar-2018, 19:10
Bearing in mind that the idea of a drum scanner is to (effectively) move a very small spot across an image, there are a couple of issues, even ignoring the mechanics of the movement, and the issue of actually generating the small spot. We want a large exposure range with at least 14 bits of image depth and we need to be able to discriminate between very similar values at both dark and light levels. Ideally, we'd prefer to limit the amount of light we get on the film to avoid it catching fire...
My old ColorGetter 3Pro did fine with 12 bits. But with today's tools, you might as well make it 16 bits. I doubt this will change the file size -- I'm thinking the 12 bits/pixel of my scanner were actually stored in a 16 bit byte (three bytes per pixel) so the file size wouldn't change if you were to use the other 4 bits for data. So why not use them if they bring value to the process?
I wouldn't worry about heating the film. To get the most out of a drum scanner you fluid mount the film to the drum, and cover it with an optically clear overlay. So you have drum, fluid, film, fluid, overlay. The film will come out of the drum at exactly the same temperature as the drum. You can't put energy into it faster than it can dissipate it into the drum.
While you might think that you are pushing all kinds of energy thought a tiny aperture and that should result in a "hot spot" on the film, in reality is doesn't. Because the light is going through that pixel for a very short time (A few milliseconds? Microseconds? IDK because I never did the calculations), the total energy transfer is very small. That said, the hugely bright xenon lamp in my Colorgetter is dumping waste heat at around 900W (I did say it was really bright didn't I?). It will really heat up any room that you run it in, and the fan noise is very high.
It's the waste heat and the noise that makes me suggest looking at alternative light sources.
Finally, if using PMTs, you'll want to look up the concept of the log amps, and how they are typically used with PMTs in drum scanners. The basic way this is used is you get to set the end points of the scan to match the film you are scanning. So you can apply the entire 12 bits the scanner can deliver to just that density range that physically exists on the film.
Said another way, your software interface lets the operator set his black and white points (three times, for three colors) for what's actually there. For a B&W negative, for example, the black point is typically set on the film rebate (scanning below "film base + fog" is sorta pointless, yes?), while your white point is set a little beyond (leave yourself some cushion) the densest part of the film you can identify. And that's the density range you scan, no more.
The opposite way to do this is to make that density range fixed, which is how most flatbed scanners work. And you'd fix that range to the worst case scenario, which would be transparencies. This is one of the reasons that most flatbed scanners (particularly less expensive ones) do a less than stellar job scanning B&W film. B&W film has a much smaller density range than tranny film does, so it can turn that 14 bits of range into 4.5 bits in a big hurry. If you like your tonality to be smooth, far better to spread your 14 bits just over the density range you need at the time. Thus... PMTs and log amp circuits.
Ted Baker
6-Mar-2018, 04:38
The opposite way to do this is to make that density range fixed, which is how most flatbed scanners work. And you'd fix that range to the worst case scenario, which would be transparencies. This is one of the reasons that most flatbed scanners (particularly less expensive ones) do a less than stellar job scanning B&W film. B&W film has a much smaller density range than tranny film does, so it can turn that 14 bits of range into 4.5 bits in a big hurry. If you like your tonality to be smooth, far better to spread your 14 bits just over the density range you need at the time. Thus... PMTs and log amp circuits.
That's not necessarily the case, though the controls to do this are often not readily explained to the user or are not directly controllable in some cases. The epson flat beds can vary the CCD exposure of all three channels (unless its faking it) and log amp doesn't really offered anything if a 16bit A/D is offered, or if multi exposure HDR approach is used.
it's interesting to learn how drum scanners work, and how they solved the problems of the day with the limitations of the technology. Some of those limitations no longer apply, the need for a log amp for example. But you still got the problem of keeping the film flat, which I guess a drumm does a good job of.
Personally I think you would have more success if you embraced some newer technologies. Perhaps a drum combined with a modified dslr, one with pixel shift so you record each spot with a correct color, or just a monochrome sensor behind appropriate filters.
Pere Casals
6-Mar-2018, 06:07
This means the AD converter has to be capable of about 1 MHz.
Obviously this is something which can be achived with this chip (http://www.ti.com/product/ADS8329/description) which costs around 15 Euros...
In fact you need 4 chips, 3 colors + IR for dust correction...
I'm a heavy user of the AD7730 part (http://www.analog.com/media/en/technical-documentation/data-sheets/AD7730_7730L.pdf), a very complex chip I know very well and I integrate in the PCBs I design, low speed and very high precision. It has MUX, instrumental amp, PGA amp, precision DA for offset generation and an internal Microcontroller for SINX and FIR digital filtration...
With the ADS8329, first is that's SAR type, requiring a very good analog signal conditioning as SAR type are not as good as Delta-Sigma in common mode noise rejection. Then one has to take a magnifiying glass to read well 10 times the graphs from page 12 (http://www.ti.com/lit/ds/symlink/ads8329.pdf) to know how many true precision bits you have at what sampling frequency.
If you want reading 4.0 densities you may need an advanced development, perhaps you may use a dual amplification of the same signal to be infeed in two separate A/D chips, and combining the result, this is the way ARRI uses in Alexas, they call it DGA, dual gain amplifier. Another way would be pulsing the laser intensity in two levels, chopping/buffering the signal for the two levels and sending it to two separate A/Ds for each channel.
What I mean is that while silicon parts are so cheap a suitable development may be very expensive and multidisciplinar.
To experiment and to have a "proof of concept" I'd recommend to take a good/suitable USB ocilloscope, 4 channels perhaps, for example Picoscope, you have an SDK https://www.picotech.com/downloads and then you concentrate in the software and in the physics, if not you may invest too much effort in the electronics before knowing if the thing has sense.
You would also need to track drum angular position with extreme precision, 1/4 of pixel perhaps, a PC can deliver 1uS realtime control, but even this soft RTC requieres a realtime extension, or programming drivers + hooking IRQs and HAL entry points, or doing it in Linux. A good way would be extrenally controlling the acquisition, so your custom electronics would only require clocking the oscilloscope and the pc, you would clock the init row in the PC software and the pixel acquisition clock in the USB oscilloscipe, so the pc would know when next sample is for the next row. I guess it can be done in this way, as you don't stress the PC realtime and the pixel clock that's hard realtime is managed by a simple custom electronics, and the oscilloscope holds all signal integrity... At least is how I would go...
At 15 rounds per second, clocking the init row in the PC it's easy, you should increase the Windows task manager granularity to 1ms (from normal 30ms) with SDK funtion timeBeginPeriod(1);
https://msdn.microsoft.com/es-es/library/windows/desktop/dd757624(v=vs.85).aspx
Then you can do it in IOPL 3, this is user mode, but process and thread priorities have to be raised to the maximum, this is REAL_TIME and TIME_CRITICAL.
Regards
barnacle
6-Mar-2018, 06:34
Yep, first thing to start with is the sensor/light source. And to start with I'd work in mono; three channels is just multiplication.
Bruce, I suspect there may still be a need for a log amp between the sensor and the ADC though basically I'd want to have a close look for any contouring (quantisation error) at both the high and low points. Though of course the target output device is also a critical part of the system.
Setting black and white levels by changing the gain and DC offset is the broadcast standard way of setting up both cameras and display devices.
Neil
Ted Baker
6-Mar-2018, 07:10
If you want reading 4.0 densities you may need an advanced development, perhaps you may use a dual amplification of the same signal to be infeed in two separate A/D chips, and combining the result, this is the way ARRI uses in Alexas, they call it DGA, dual gain amplifier. Another way would be pulsing the laser intensity in two levels, chopping/buffering the signal for the two levels and sending it to two separate A/Ds for each channel.
Or you could just do multiple exposure, with differing exposure times, a few of the smartphones take this approach. Drum scan after all is a multiexposure device in the first place no?
Pere Casals
6-Mar-2018, 08:42
Or you could just do multiple exposure, with differing exposure times, a few of the smartphones take this approach. Drum scan after all is a multiexposure device in the first place no?
Well, in fact when I suggest "pulsing the laser intensity in two levels, chopping/buffering the signal for the two levels and sending it to two separate A/Ds for each channel." this is a Multi-Exposure (dual) system in a single pass,
You would make two short laser shots, buffering+chopping the signal very fast (two time per pixel) while allowing the converters a full pixel clock time interval to make the conversion.
Ted Baker
6-Mar-2018, 08:56
Well, in fact when I suggest "pulsing the laser intensity in two levels, chopping/buffering the signal for the two levels and sending it to two separate A/Ds for each channel." this is a Multi-Exposure (dual) system in a single pass,
You would make two short laser shots, buffering+chopping the signal very fast (two time per pixel) while allowing the converters a full pixel clock time interval to make the conversion.
I guess they are all variations on the same theme. i.e. bringing the voltage variation into the best range of the A/D and ultimately the bit buckets you have available to fill.
Possible problems with a laser I guess would be finding one with a sufficiently broad spectrum, or calibrating it, or maybe not if you carefully calibrated it to match the emulsions, etc. But with the later you would be digitally simulating the color cross talk engineered into the emulsion. So maybe you be better off with just a digital camera... ;)
interneg
6-Mar-2018, 11:33
In fact you need 4 chips, 3 colors + IR for dust correction...
You don't need IR dust removal on a fluid mounted scan... There was one (Dainippon Screen 1030ai - I think) scanner that had a 4th PMT intended for optical unsharp masking, but I can't think of any others that had more than three PMTs
Pere Casals
6-Mar-2018, 11:42
Possible problems with a laser I guess would be finding one with a sufficiently broad spectrum,
Laser light is both monochromatic and highly coherent, this is that even the photons are in phase !
For color scanning, an scanner does not need a broad spectrum in its light components, at the end color dyes in film are a response to silver content in the development, so just reading in the dye peak (for example) it would determine the in film native signal. Add a calibration and you can determine near exact native film spectral result.
What I mean is that for scanning a low CRI light source may be ideal, because at the end scene spectral information is not there anymore, just a tristimulus repersentation of it. This is IMHO...
If we scan Velvia we won't be able to see the same in an sRGB monitor, just the triangles are not the same, nor the possible static contrast. One may say that an scanner delivers nicer colors than another one, but it's about calibration or 3D LUT edition...
Pere Casals
6-Mar-2018, 11:46
You don't need IR dust removal on a fluid mounted scan... There was one (Dainippon Screen 1030ai - I think) scanner that had a 4th PMT intended for optical unsharp masking, but I can't think of any others that had more than three PMTs
true...
Ted Baker
6-Mar-2018, 12:11
Laser light is both monochromatic and highly coherent, this is that even the photons are in phase !
For color scanning, an scanner does not need a broad spectrum in its light components, at the end color dyes in film are a response to silver content in the development, so just reading in the dye peak (for example) it would determine the in film native signal. Add a calibration and you can determine near exact native film spectral result.
That's what I used to think... Until I tried to understand why the gamma curves of color negative film do no match, and there is no such correcting gamma in color print film/paper.
For example the CC graphs are prepared using status-m which is a narrower spectrum than what the print sees. The gammas when measured using a broader spectrum are closer to equal, the gammas are different again when the emulsion is exposed to a narrow spectrum of light that only hits one layer.
This intentional crosstalk designed into the emulsion would be missed or at least you would see a different version of it depending where you take you measurements.
This cross talk is designed to manage saturation, at different densities among other things. I am sure you could model it, but then why not use a digital camera if you going to model nearly everything... ;)
Pere Casals
6-Mar-2018, 13:13
That's what I used to think... Until I tried to understand why the gamma curves of color negative film do no match, and there is no such correcting gamma in color print film/paper.
For example the CC graphs are prepared using status-m which is a narrower spectrum than what the print sees. The gammas when measured using a broader spectrum are closer to equal, the gammas are different again when the emulsion is exposed to a narrow spectrum of light that only hits one layer.
This intentional crosstalk designed into the emulsion would be missed or at least you would see a different version of it depending where you take you measurements.
This cross talk is designed to manage saturation, at different densities among other things. I am sure you could model it, but then why not use a digital camera if you going to model nearly everything... ;)
Gamma, 1D LUTs, etc may work in practice, but the complete spectral characterization of a film would require a 3D LUT.
You can reduce the problem to a 3D LUT, in the technical 3D LUT sense, not in the creative 3D LUT sense (anyway LUT format it's the same in both cases).
In practice you have to create/calibrate a Technical 3D LUT for each film, because every film has an spectral nature. For digital usage a 3D LUT calibration has all. Still you may not be able to show all what's in the film because color spaces are not equal.
If you want to reproduce the spectral footprint of a film (say an slide) then it's also possible in theory, but then for each RGB entry point of the LUT you have to record the spectrum in the original calibration spot, this would be useful to transalate to other color spaces with best matching possible...
In fact it is how it worked color separation in BW films (Kodak 2237 and 2238) for preserving movies. It's the same I mentioned but done with analog tools, when restoring the separation to a color medium a matching spectral footprint medium can nail the original, even spectrally.
Ted Baker
6-Mar-2018, 13:58
Gamma, 1D LUTs, etc may work in practice, but the complete spectral characterization of a film would require a 3D LUT.
I agree to complete an accurate characterization of a film would require a 3D LUT. However it makes sense to have as a starting point a measurement that is closer to physically reality. In particular having the sensor pickup the cross talk in emulsions rather than simulating it through a matrix.
Interesting the color separation film you mentioned are also designed to work with DPX/Cineon which is the scanning technology that is used to capture the film in the first place. DPX is specifically designed to mimic the spectral sensitivity of the print film, as it was originally designed as camera negative to digital then back to print film system. (Or at least to match the Vision 2 stocks of the time).
I am of course making perhaps the erroneous assumption that one of the reasons for using film is to retain its unique characteristics which are not easily replicated. :D Indeed with a 100% accurate characterisation there is no need for film!:eek:
But if you can build your own drum scanner I am sure you can solve this problem too.;)
Peter De Smidt
6-Mar-2018, 16:07
It is an interesting discussion that would apply to all types of scanners. Do you just need good output at the optimum r, g, b frequencies for the receptor, or is a smoothly continuous spectrum better? With my Dslr scanner, our first light sources went the RGB approach, but currently we are testing very high CRI sources.
Pere Casals
6-Mar-2018, 16:46
It is an interesting discussion that would apply to all types of scanners. Do you just need good output at the optimum r, g, b frequencies for the receptor, or is a smoothly continuous spectrum better? With my Dslr scanner, our first light sources went the RGB approach, but currently we are testing very high CRI sources.
Peter, think that drum scanners illuminate with lasers, and a laser it's pretty monocromatic, so CRI is extremly low, while nobody has ever complained about colors comming from a drum.
IMHO a high CRI illumination only worsens things in a CCD scanner, as we have some "cross talk" or channel mixing from the overlap of CCD channel spectral width , while a per channel monocromatic illumination, placed in the peak, would have low inter channel mixing, this is IMHO, it's what I concluded without having read it, so that thought should be checked, but also IMHO it explains that color purity from drums.
calebarchie
7-Mar-2018, 01:01
Drum scanners do not use lasers.... the later hi end ones used rather costly xenon lamps.
Pere Casals
7-Mar-2018, 01:07
Drum scanners do not use lasers.... the later hi end ones used rather costly xenon lamps.
Not all the drums illuminate with lasers, I had to say "best drum scanners" illuminate with lasers, sorry.
"Drum Scanners spin your original Film around on a drum while a fixed laser or other beam of light looks at the Film as it spins."
http://www.spectra-imaging.com/drum-scanning.html
calebarchie
7-Mar-2018, 02:21
I think is a common misconception, I am not aware of any that use laser sources. Can you provide links or model?
I don't think chromagraph pictured has laser.
Ted Baker
7-Mar-2018, 02:21
It is an interesting discussion that would apply to all types of scanners. Do you just need good output at the optimum r, g, b frequencies for the receptor, or is a smoothly continuous spectrum better?
IMHO the spectral response should match the target, i.e. the eye or a print film (which is slightly different I believe). Its a complex problem and I don't think there is an easy answer, because too much overlap and you will see more cross talk than the eye would see. I think It becomes more difficult to model when you consider the non-linear response of film. In particular print film where the gamma is substantially different from real life, it being about -0.6 instead of +1.
My casual interest is studying/developing a solution to invert print film so I am interested in the additional complexity this entails, but hopefully they are still making e-6 materials by the time this project is finished ;)
calebarchie
7-Mar-2018, 02:29
Nvm, that was an imagesetter..
After some digging, found the chromagraph S3400 (pictured) uses an osram 12v 50W halogen - not dissimilar to the ones in my drum scanner.
Patrick13
7-Mar-2018, 08:39
At this point it's going to be far better to design a laser driven system using mirrors for the movement across the film and avoid that whole spinning wheel of death thing altogether.
You should probably aim to make the scanner "More Human Than Human(tm)" instead of trying to replicate ancient technology.
Just an opinion :rolleyes:
" . . . instead of trying to replicate ancient technology . . . "
. . . is the key to this discussion.
Drum scanner technology was a wonderful application of extremely precise mechanical and electronic control using the best of last century's tech. But even using moving mirrors and lasers instead of rotating metal/acryllic drums to scan film is archaic.
The nano-precision of step and repeat lithography creation of high-density digital sensors and the application of those stationary sensors for acquisition of film images is, IMHO, already superior to that which we used to obtain from rotating scanners.
With a drum scanner, all the precision necessary for the mechanical process is required with each and every scan. With a digital sensor, the necessary precision is "baked into" the creation of the sensor, once, leaving the system forever free of that overhead.
And digital sensor manufacture and software processing of images is but in its infancy.
Rich
Adam Long
7-Mar-2018, 13:38
After starting this thread, I stumbled upon two ScanMate 5000 scanners. Not to far away of my home town. I took a look on them on Sunday and consider to buy both of them. One is broken, but the current owner thinks it should work, after fixing some damage done during transport. The second one is in working condition. I could use one to scan for now, have the second for spare parts and also as base for the DIY scanner project. We the working one (preview, focus and white point calibration), but could not do any scans, as the software lacks a dongle and we could not figure out how to get into demo mode. Next Sunday I will know more, as I bring my own old computer with SCSI connector to test...
I'd recommend you buy them.
I did exactly the same five years ago - £240 for one 'working' and one 'broken' Scanmate 5000, with four drums in varying condition. I couldn't test either machine so it was a gamble.
Thankfully there is an excellent Scanmate resource on the rangefinder forum:
https://www.rangefinderforum.com/forums/showthread.php?t=139096
With the aid of that I soon had both working great. It was clear from the interiors that the 'broken' machine had had much less heavy use, so that is my main machine. The main issue I had was getting a mounting station, took me a few years and cost more than the scanners.
I'm sure you'll learn a lot tinkering with these scanners, they are very nicely made, compact and quiet. And the results are excellent.
calebarchie
7-Mar-2018, 13:56
At this point it's going to be far better to design a laser driven system using mirrors for the movement across the film and avoid that whole spinning wheel of death thing altogether.
You should probably aim to make the scanner "More Human Than Human(tm)" instead of trying to replicate ancient technology.
Just an opinion :rolleyes:
Flying spot scanners have been around for a long time too...
barnacle
9-Mar-2018, 12:20
Indeed; flying spot telecine using a raster generated on a cathode ray tube is (was) a common way of turning both still and moving images into TV signals.
Regarding lasers, as discussed above - if you're going to do it that way you'll need a red one, a green one, and a blue one. Because you're looking for absorption at the specific colour, not at a position. I'd assume, for the same reason, that the halogen lamp approaches have very good filters between the light and the film.
Neil
Ted Baker
10-Mar-2018, 14:07
Just doing some light bed time reading, Hunt's "The Reproduction of Colour". I can't find the quote now but in it he talks of the difficulty of matching the spectral response with a sensor. In particular where colour couplers are used in a negative. The dyes spectral response then tends to be sharp cut on one side (towards red), and not so sharp on the other, though I think this also applies to transparency but not to the same say degree.
IMHO for a transparency if you can mimic the spectral response of the eye your probably gold. A DSLR is probably very good at this and will just get better.
With my Dslr scanner, our first light sources went the RGB approach, but currently we are testing very high CRI sources.
If you compare lamp spectrum in Scitex Smart scanners and later Eversmarts you can see that they added yellows and surf greens. That was done for a reason.
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