Using Commodity Hardware in Laboratories?

PhysicsTom asks: "I am a Senior Physics student who's final year project is based upon using common, easily available technology to replace parts of the aparatus used in various departmental labs. Currently, my main area of interest is trying to integrate certain computer peripherals (such as scanners and digital cameras) into experiments at an earlier stage, so that images gained from the experiments (such as difraction patterns, etc) can be analysed in a program such as MathCAD straight off, rather than the much less efficient methods we're using at the moment. The problem is that I am having trouble finding out about the way in which scanners and digital cameras work, and how this would affect their accuracy with respect to what I am aiming to do." Basically, how do the various hardware aspects of such devices affect their ability to accurately measure or scan the subject of the experiment?

"The information I am looking for includes things like: the resolution of their grey-scales, what degree of accuracy the motor steps at, how uniformly distributed the CCDs are in the arrays, and other issues that might affect accuracy. Just so that I can know how close to the 'real' picture what I get out of the scanner/camera is. If anyone can tell me all these boring facts for any suchequipment (preferably solutions currently available in the UK) then I would be very appreciative."

Comments

Contact the manufacturer

[wiredog]

The grey scale should be in the documentation. CCD density can be calculated by width of scanner bar divided by number of CCD's. As for the rest, you may have to track down the manufacturers engineers. An alternative is to take apart a scanner and find out who manufactures the components, and contact them. Good luck.

Contact the Product's Maker

[Motheius]

Have you tried contacting the manufactuer of the products you are using? I don't mean as joe student, I mean as a represenative of your university. You might be able to get more then just the specs to the equipment. You might be able to get donations.

You're going to have to measure it yourself

[jmichaelg]

If you're relying on your equipment to give you reproducable results, you're going to have measure what it's actually capable of and not rely on published specifications.

I stopped relying on spec sheets when I discovered they weren't very accurate. I've seen variances as high as 50% off spec.

Happy Medium

[Root Down]

Basically, how do the various hardware aspects of such devices [scanners and digital cameras] affect their ability to accurately measure or scan the subject of the experiment?

Well, it would all depend on the time quanta that you are measuring. Digital scanners for anything having velocity are right out the window, since it takes a notable amount of time to capture the image. Digital cameras are somewhat faster, but it would depend on the quality of the camera if you wanted to track moving objects at higher 'shutter speeds' and resolutions.
If a regular camera could capture the data you are collecting - and it seems that this is the case - the digital cameras should be fine. The important issue is that higher resolutions take longer to fix the image. Finding a happy medium between image resolution and image capture is what you're looking for. You might be able to get those specs from the manufacturer(?).

Do your own measurements.

[Mochatsubo]

I am looking for includes things like: the resolution of their grey-scales, what degree of accuracy the motor steps at, how uniformly distributed the CCDs are in the arrays

The best thing to do, when possible, is to do the measurements yourself. That way you know exactly what *your* device is capable of doing, and not the *average* device from the manufacturer. You shouldn't rely on manufacturer's spec sheets for this type of information.

For example, you can get a quick idea of the bit depth of a CCD by measuring the noise floor of the output of a null signal and compare it to the output of a saturated signal. You will find that most *consumer* or *security* CCD cameras will not give you a full 8-bits. Even scientific CCDs which state that they give a full 8-bits are only under certain conditions with a specific type of average or weighted measurement. Don't trust the spec sheet. Measure to make sure!

Then of course you could also use your head. How uniform are CCD arrays (spatially)? Think about how they are made. They are very uniform.

Finally, you should talk to your final project advisor. What you are doing isn't Physics, it's Engineering. Sure engineering is part of experimental science, but shouldn't be the prime focus of a "Physics" project, IMO (was a Physics undergrad myself).

SANE is a key resource

[tshoppa]

You explicitly ask about directly interfacing to scanners and digital cameras - my preferred open-source way of dealing with these peripherals is SANE.

The SANE folks have gone to great efforts to get various scanner/camera devices to work in an open source environment. In some cases the manufacturer provided all the information needed to interface to the device; in other cases the interface has been found exclusively through reverse-engineering.

I highly recommend that you look closely at the list of supported SANE devices and choose a device known to work from the list. If you go into your local computer store and buy something off the shelf without looking at the SANE list, you are *very* likely to end up with a product that is completely unsupported in any useful environment.

Keyword: photogrammetry

[paulwomack]

You're rediscovering the science of photogrammetry.

Here a potted google search.

BugBear

this hardware exists.

[Rev. DeFiLEZ]

OK, just so you know the company i work for is solutions provider for the medical/atomic/chemistry fields so we sell things that you desire (a scanner thats good enuf for xray film). there are a couple of places where you can get this stuff. in the US there is a company called "cobra scan" (i think , its close enough to find them) and while their scanners look pretty shitty, they will fly someone your lab to calibrate the scanner to your acceptible margin of error, another company called vidar sells scanners that are very nicely built. these scanners are much more pricey then most (~7kUSD) however they have the accuracy you need and still used standard twain drivers and can most likey get them to work in what ever enviroment you have.

something you should go and check out is a trade show RSNA which shows up medical scanners and other imaging hardware that can be usefull to you.
RSNA is held in chicago.

-rev

Some random recommendations

[OpenMind(tm)]

• Don't use consumer low end devices where color is an important factor. Scanners in particular tend to change their color characteristics after calibrations, with changes in lamp temperature and other environmental factors.
  
• Don't take pictures with low end cameras and use them for later analysis, particularly when looking for positional data. Compression artifacts stand to introduce substantial errors even on low compression settings. If you can turn off compression entirely, this may be an option. Live capture from a video stream would probably give you better images not limited by the device's intended use.
  
• Keep in mind the low quality of lenses on most digital cameras and camcorders and the possibility of geometrical abberations near the edges.
  
• Get some good visual benchmarks.
• Consider that the cost savings may not bear out the work needed to make sense of the data. Commodity products are not made for precision.
  

Remember the Hubble Space Telescope

[OpenMind(tm)]

Keep in mind that good postprocessing can factor out all sorts of predicatable equipment shortcomings. When the Hubble Telescope went up with a seriously flawed mirror, good software made it possible to get scientifically valid results without replacing the flawed optics. A similar approach might be useful here, if you're interested in this aspect of the problem.

Also, keeping benchmarking data such as a color test image in field in each of you data images could allow for per-image calibration and factor out some of the unpredictability of consumer imaging. This could be easily automated in software.

light intensity

[emg178]

I worked in a lab where the intensity reading of each pixel was important. We used scientific grade equipment, so that we could set the sensitivity, offset, and correction.
If you are interested in measuring the intensity of each pixel, read on:

First of all, I would think that a consumer camera with automatic exposure control would automatically set the gain (or sensitivity to light). You would need to be able to turn this off.

Secondly, the offset has to do with black noise (or error due to thermal energy within the ccd). On the camera's that I used, it was around 5 intensity levels out of 256 on an 8 bit camera. There is not a need of refining this on consumer equipment, so it probably doesn't get much better than that. You can buy cooled camera's for getting rid of this, but you want it cheap so this is not a great option. You could try cooling the camera w/ liquid nitrogen. I wondered about doing this myself. Alternatively, if you are taking images of something that doesn't change in time, you can take multiple images and average them. The black noise of the averaged image will decrease as the square root of the number of images.

Thirdly, the image correction -
Most consumer equipment uses a gamma correction curve b/c of similarities w/ film and video. Look it up if you don't know about it, it is interesting, and useful for taking pleasing photographs. For scientific purposes, though, you probably want a linear response. This will give you a constant sensitivity to light changes.

The last thing you should be concerned with it changing conditions / response with time. Some others have noted this. You will need to calibrate the device many times at different times of the day to make sure that changes over large times are reasonable. We utilized a calibration during the experiment to reduce this problem.

As for image formats readable by mathcad / matlab, etc. That sould be fairly easy once you get the device driver settled.

Scanner References..

[jdrogers]

I just asked a Professor here at the optical sciences center if he knew of any good publications on scanner technology.. He said to check out books/papers by Leo Beiser. He has apparently written some books on Optical Scanning technology and various SPIE papers as well. This may give you a starting point for a more rigorous look at the tech behind scanning.

Re:Hear hear!! (Too late to change your topic?)

[ninewands]

An easy way to calibrate the color and/or gray-scale response of a scanner ( or digicam ) is to go to your local high-end photo store ( one that deals in darkroom equipment ) and buy a color standard card. Kodak publishes them for use in calibrating color printing equipment and evaluating filter packs for color enlargers, and they are QUITE accurate. They also have a gray-scale reference card available. While this won't be as accurate as calibration against NIST primary standards, they don't cost as much either. These cards are NOT expensive, but the old, immutable rule is true. Cheap, fast, good ... pick two. Do NOT use a laser printer for grey scale standards. Even inexpensive scanners can be set to use interpolated scanning at high enough resolution to resolve the toner particles.

As for x/y positional calibration, I made up a template for fret placement on a guitar fingerboard, once upon a time, by computing and plotting the fret placement in AutoCad and printing it out on a laser printer. The finished home-built instrument played scales more accurately in tune than my commercially-built acoustic guitar did. Or, if your school has a machinist on-campus, see if you can obtain a set of Jorgensen blocks and scan them. They are sized accurately to, IIRC, 0.0001 inch, or so. If you decide to use a laser printed calibration chart, be SURE you use a grid, rather than, say, a rectangle of a certain size. This way you will be able to determine whether there are any non-linearities in the motion of the scan head.

Accurate calibration standards just aren't THAT hard to find.

Re:No guarantees

[darkonc]

This doesn't mean you can't use them, though. What it does mean is that you'll need to select something you're pretty sure can handle what you want, and then devise procedures for calibrating the devices' output.

Note that even NASA continually re-calibrates their probes -- and I presume that Nasa doesn't use off the shelf components for most of their deep-space boxes. Units will change over time -- much less the change between units of the same model. Whatever you choose, you'll have to do calibration on an ongoing basis.

Once you figure out how to do calibration, you can compare various units (and report back! :-). If you do a good job, you might even be able to scam yourself some free units from manufacturers who are interested in the results, and having them published.