Microdensitometery for understanding Stand Development

Discussion in 'B&W: Film, Paper, Chemistry' started by Tom Hoskinson, Aug 25, 2005.

  1. Tom Hoskinson

    Tom Hoskinson Member

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    Pyrocat-HD is my primary film developer and I use it with either minimal agitation or semi-stand agitation. I can see positive differences in my LF contact prints and would like a better understanding of what is going on.

    The approach to understanding that I favor is a Statistical DOE (Design Of Experiments). In order to accomplish this I need to make repeatable, quantifiable (and applicable) measurements.

    My old Perkin-Elmer microdensitometer is not up to the task.

    Can anyone identify a microdensitomery instrument (or alternative) which has the right spectral response coupled with the requisite spatial resolution to quantify changes in microdensity?

    Any recommendations?
     
  2. Photo Engineer

    Photo Engineer Subscriber

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    Tom, please let me clarify one point for you.

    Several of my techie friends have told me that a scanner can be used as both a densitometer and a microdensitometer. I have not personally reduced it to practice, but merely have their description of how it is done.

    Basically, as I understand it a set of micro and macro exposures are made and scanned at very high resolution. Then they are all displayed at the same magnficatation on-screen in Photo Shop (forgive the digital here all), and the densities are plotted as a function of distance across the exposure, and also as a function of Log Exposure, so you have a micro denstiometer trace of the line, and the characteristic curve that a particular size line will yield. By further manipulation you can then display the macro and micro images at the same magnficiation and view and compare the results.

    One of the problems is that you must have a practical microsensitometer to get the original images, and to do that you need appropriate charts for making the exposures. So far, I have the charts, but that is about it.

    Forgive any errors above and any misunderstanding, but I am strictly an analog person and do very little digital at all. I am still learning how to use a scanner properly.

    I think your effort here is quite commendable. I will try to do all I can to get some kind of support going at this end from some my former associates here. They may have some suggestions that might help.

    PE
     
  3. gainer

    gainer Subscriber

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    Excuse me for butting in. Silicon phototransistors are obtainable with very small apertures and very high sensitivity and linearity. High quality silicon diodes have an exponential voltage-current transfer which, in the feedback loop of a high quality operational amplifier with the phototransistor connected as a current source to the inverting input of the op amp, provide an output that is accurately the logarithm of the input times a constant.

    The aperture of the photocell is ot necessarily the limiting factor, as we are planning to look at very small parts of negatives which an be greatly enlarged, imaged on a very small aperture. A further consideration is that for first attempts, extremely accurate measurements of absolute density may not be required. You will be looking for very small changes in density over very small distances.

    Just some thoughts for anyone who wants to try it.

    I have done the scanner thing, but in order to get a wide range of densities you need a lot of bits per sample. My equipment would only allow 256 gray levels, the increments of which get larger as the level gets smaller in log terms.
     
  4. Kirk Keyes

    Kirk Keyes Member

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    Tom et al. - I don't have time now but I'll get my thoughts on this to you all tomorrow.
     
  5. Tom Hoskinson

    Tom Hoskinson Member

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    Thanks to PE and Pat for their suggestions.

    Looking forward to your input, Kirk.

    I think one of the keys to this is sufficiently high spatial resolution. It seems that Zeiss has a scanner/optical microscope based microdensitometer with resolution in the 7 micron range. I would like to do better than that if I can.

    A colleague of mine has interfaced a sensor with an optical microscope to scan Xray film and TEM film. I will take a look at that as well.
     
  6. Kirk Keyes

    Kirk Keyes Member

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    OK - Here's my initial thoughts on the subject. (I love instrument and analysis design, by the way.)

    I see two basic approaches. One can either:

    1) make something, or
    2) adapt existing equipement.

    With that in mind, let's look at Option 1. Going with Patrick's excellent suggestion of using silicon phototransistor would be the first step. Some method would be needed to convert the voltage signal from the op amp into something usable, i.e. a volt meter at the least.

    1.a) Adding on to the phototransistor idea, some sort of an optic path would be needed to isolate and focus on a small section of a negative. And a light source as well. And finally, some sort of mechanism like a micrometer to move the negative.

    For this approach, probably basing the design off of traditional microdensitometers would be best. That means a microscope-like type of optics would be needed.

    This may be a lot of work. Data collection from the volt meter and then conversion to density readings could be painful for the number of readings that would be needed.

    Perhaps easier, would be:

    1.b) Keep the negative in a fixed location, and move the sensor. Some sort of mechanism could be used to move the sensor under a projected image of the neg. Using an enlarger (which most of us already have) to focus and project the image onto the baseboard, a baseboard densitometer like the phototransistor/volt meter combo or perhaps easier, something like on of the old Minolta PM densitometers could be used. The PM (or other baseboard meter) would be direct reading in density, so that would simplify the conversion of voltage readings in to density.

    Things to keep in mind with this approach:

    1.b.1) Move the enlarger up as high as it goes to increase the image size, as well as using a shrt focal length lens to increase the amount of magnification at the baseboard. (We don't need the lens to cover the entire neg, just something that will project a sharp and contrasty portion of the negative.)

    1.b.2) Mask the opening of the sensor to get a smaller aperature to further increase the effective magnification. Ideally, the size of the aperature should be somewhere around the step size of the linear distance that the sensor will be moved.

    1.b.3) Use a set threaded rods (i.e. long screws) to make a "sled" for the sensor to sit on, and then a "dial" could be added so that fine turns of the rod could be measured. A 1 mm pitch rod being turned 15 degrees per step would be 1/24th of a mm increments. Multiple by the baseboard magnification to get the actual step sizes on the negative.

    1.b.4) Use of the color filters of the Minolta PM (or other) baseboard densitometer unit could be used to isolate color/stain effects.

    For Approach 2 - using existing equipment, off hand, I can think of:

    2.a) find a microdensitometer of some commercial equipment that is similar in function. If actual microdensitometers were easy to come by and cheap, we would not be having this thread...

    But I think Tom has a good approach - use a microscope with a digital cameral and take images of the film. I spent about 2 hours trying this one afternoon at a friend's house who is a microscopist. He had a nice Zeiss scope and a digital camera that is designed for use with the scope. I had issues with getting enough magnification while still keeping the image sharp. The contrast was not what I was hoping for as well. And then I had problems getting the image bright enough to shoot with the camera. (I burned a few holes in the test neg a could of times before I figured out how to not do that!)

    But I think this idea has a lot of merit. But it is not a cheap solution for those of us that do not have access to expensive scopes and digital cameras. So on to the next idea:

    2.b) Film Scanners - I think this apporach should be a good one, and since many of us already have scanners, then that is one big hurdle down as far as the equipment side of this problem goes.

    2.b.1) Resolution - I have a Nikon Coolscan V that can do 4000 dpi. That's about 157 points per mm. Looking in James and Mees' microdensity plots, that looks like it should be sufficient, if not just what is needed. Even though that scanner only does 35 mm format, cutting negs up to feed it should not be a issue.

    2.b.2) Data Collection - another big plus for the scanner, simply scan the film. Once the scan is in the computer, then we can use software to get the density readings.

    Take a look at this page: http://www.efg2.com/Lab/ImageProcessing/TestTargets/ (this will be useful for our next big project on how to test for resolution!) and then notice the graphs at the bottom of that page - they used the software that can be found here: http://www.efg2.com/Lab/ImageProcessing/PixelProfile.htm

    I've played with the Pixel profile software and it is pretty simple and easy. Bring a picture into it, drawn a line across the image, and then it makes a spreadsheet page full of data from the pixels under the line.

    The issues I can forsee with this are not enough resolution in the scanner's density readings - scanners are designed for macrodensity and probably not as much for microdensity. I have a feeling that 8-bit resolution will not be enough. So perhaps 12 or 14 or 16 bit image files would be usable. (I don't know if the Pixel-Profile software can handle these files, then then we can do stuff in photoshop to extract a set of pixel data I'm sure.

    And in general, Ron and Patrick are right that calibration issues will be important. Especially after reading Dr. Henry's account of his attemps at microdensitometery in "Controls in Black and White Photography".

    And targets as well. Perhaps Ron could elaborate on the target he has. I was thinking that a USAF 1951 contact target for resolution would go a long ways here, but the chrome on glass ones that would be best are pretty spendy. I figured photos of the large USAF 1951 target that Edmunds Scientific sells would be good for starting - it has high and low contrast patches, as well as R, G, and B ones.

    Hope this gets the ball moving along on this idea! See, I told you I like this sort of stuff!

    Kirk - www.keyesphoto.com
     
  7. mikewhi

    mikewhi Member

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    Hey, I recall that in the movie ALIENS, the robot-thingy made a handheld device to locate the aliens by identifying micro chances in air density. Apparently when aliens crawl along they screw up air density.

    Do you think that could be adapted to suit your needs?

    -Mike
     
  8. gainer

    gainer Subscriber

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    When you are probably not required to read the whole density range of the negative at one setting, The scanner approach may (should) allow biasing the level so that the desired range of densities is in the higher resolution part of the scanners brightness range. E.G., if you are looking at an image of a knife edge, you are more interested in the shape of the top and bottom of the image than in the slope of the drop from top to bottom, and can read the two parts separately. For analyzing such edges, shape is more important than absolute amplitude, I would think, especially if there is an extended enought area on each side of the edge that you can read it with an ordinary densitometer.

    The easel densitometer that I have built and use has both level and sensitivity knobs. I can set the sensitivity to read Zones once I have calibrated it for paper and VC filters, and I can set it to read density of a very small spot, less than 1/2 inch across. The meter is a digital panel meter that can probably be bought for about $15 and has a quite high sampling rate. The phototransistor has a very high frequency response, so I can move the probe around the projected image without waiting for the reading to settle down. Most of the circuitry is in the voltage regulated power supply, and that's not much. It only needs + and - 10 volts. When using it to make measurements I have found that the enlarger lamp is the biggest source of error due to line voltage fluctuations. I do my measurements after most of my neighbors have gone to bed.
     
  9. gainer

    gainer Subscriber

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    "less than 1/2 inch across" should have read "less than 1/32 inch across"
     
  10. Tom Hoskinson

    Tom Hoskinson Member

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    Thanks, Kirk and Pat.

    I have a Nikon Super Coolscan 8000 ED scanner that will handle negatives up to 6x7 cm and has 4000 dpi resolution. I'm going to try it, but I have my doubts that it is going to do the job in terms of contrast resolution.

    My second approach is the microscope/camera approach. I have image processing software that will handle 16 Bit B&W.

    My Macbeth color densitometer has a spot size that's in the size range Pat describes and I've had no joy reading microdensity with it.

    What I'd like to be able to do is produce a density line scan across a nanometer scale region of the negative and I will need a submicron spot size to do that (plus a really good stage).
     
  11. Photo Engineer

    Photo Engineer Subscriber

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    Has anyone considered the fact that with the decrease in analog film sales, some of the photo manufacturers may have some surplus equipment that they would sell for a song? It may even be possible to get them to donate it if the cause could be shown to be worthy.

    I know that a lot of old eqipment that is out of vogue and no longer used is often scrapped outright, so why not try to get one. Kodak used to maintain a salvage yard where you could buy old junk as scrap. Maybe something like that could be arranged with Kodak or any of the other companies.

    Well, just a thought.

    PE
     
  12. Tom Hoskinson

    Tom Hoskinson Member

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    A good suggestion!

    We get all the Govt. surplus lab equipment lists and we also regularly check with industry for surplus lab equipment. We've (my company) picked up a couple of Hitachi TEMs at bargain prices and a lot of smaller items as well that way.
     
  13. Kirk Keyes

    Kirk Keyes Member

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    Mike, get me one of those devices and we can see. No need to send along an alien at this point though...
     
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  15. sanking

    sanking Member

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    If we are to be on the same page with these experiments I think the scanner concept, if it works, would be the best way to proceed since it there for all of us. Not sure how much real optical dpi is needed, but if 4000 dpi is ok then I have plenty since I can scan at a real optical 5060 dpi, with easy access to 8000 dpi. And the technology is improving and getting less expensive.

    I don't know the Pixel software. Is it available for Macs?

    Don't know for sure if it is relevant but Henry in Controls in Black and White Photography has some information on targets.

    Sandy
     
    Last edited by a moderator: Aug 27, 2005
  16. Tom Hoskinson

    Tom Hoskinson Member

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    I agree that the scanner approach should be the first priority. The astronomers at Harvard are currently in the process of scanning the entire Harvard Astronomical Plate collection using a flat bed scanner and their initial reports look promising. Microdensitometry is one of their goals.

    I have two scanners:

    1. Nikon Super Coolscan 8000 ED: 4000dpi Film scanner with up to 6X7cm capability.

    2. Microtek i900: Dual Flatbed (reflection and transmission beds) capable of scanning film up to 8x10:
    - Emulsion Direct (glassless) Imaging Technology
    - Samples each scanned line multiple times, then obtains an average
    - 4.2 maximum optical density
    - 3200 x 6400 dpi optical resolution
    - 48-bit color

    A standardized resolution target is strongly recommended. The AF 1951 Tri-Bar target is one possibility, I have several of these and they are commercially available.
     
  17. Kirk Keyes

    Kirk Keyes Member

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    Available for the Mac? HA!

    Sorry - It doesn't look like it. But I'm certain something is out there that you can use. Especially if you are on OS X. There's bound to be some Linux app that could do this for you. I'm just not up on my Linux stuff these days.

    Henry does go into a lot about the issues of getting comparable numbers to Kodak. Certainly something to think about.
     
  18. Kirk Keyes

    Kirk Keyes Member

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    Tom, is that the chromium on glass USAF target?

    Tom, Ron, can you guys make some sample target films for those of use interested in trying. Actually, if two of us get something they think is working, it would be nice to have a source of (at least) nearly "identical" targets to try and compare numbers with. Somthing with not much edge effects and then something with would be good to start with.

    I was thinking that perhaps Stouffer step wedges would make good targets to try - and I mean that actual Stouffer wedge. I hope they are processed to fairly close QC controls, and may be similar in edge effects from wedge to wedge. I was thinking that one could measure the transition from say Steps 2,11, and 20 (or pick your preference) to the middle section, or from adjact steps to one another.
     
  19. Kirk Keyes

    Kirk Keyes Member

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    Tom wrote: "What I'd like to be able to do is produce a density line scan across a nanometer scale region of the negative and I will need a submicron spot size to do that (plus a really good stage)."

    Wow Tom, that's not microdensitometery. That's atomic densitometry! I think those are pretty abititious goals, and not even achievable with optical methods. Remember your light wavelengths go from 400 to 700 nm. And you want resoultion that is submicron (1,000 nm)?? Time to pull out the electron microscope at that point.

    PE wrote, "Has anyone considered the fact that with the decrease in analog film sales, some of the photo manufacturers may have some surplus equipment that they would sell for a song? It may even be possible to get them to donate it if the cause could be shown to be worthy."

    If you have some time, could you look into the surplus idea. I suspect even surplus the price would be pretty astronomical (relatively speaking). However, if you can get your old buddies at EKR to donate a microdensitometer, I would be willing to house it and operate it for all interested parties. :^)

    Pat - can you give some links to the digital panel meter you like. Anything with a serial out would be nice too. And how about some recomendations on the phototransistor? Some place like Digikey would be cool.

    Does your enlarger have a voltage stabilizer on it? How about replacing the lightsource with something that could be better stabilized, led or laser perhaps. We don't need something that covers a wide area of the neg. A lot of intensity in a small area is fine. A red or green laser pointer with a bit of opal glass would make a nice light source that one could place right up against the portion of the neg that one was interested in.

    Adding a stepper motor with perhaps a couple of speeds to the threaded rod idea above would add a bit of automation to the process, and help insure some uniformity to the process. A slow speed for doing fine detail, and then a higher speed for larger areas. Todd and Zakia in "Photographic Sensitometery", 1969, mention that calibration of the microdensitometer can be done by tracing across large areas of a step wedge to see the response of the detector with macrodensity steps/levels.

    Another idea for data acquisition would be to use a computer sound card. Most sound cards are 16 bit minimum, and that would be enough resolution to extract microdensity measurements. Combining the stepper motor sensor stage with a sound card would make generating the data much quicker.

    Another idea for a jury rigged design - I have a couple of identical student microscopes from my childhood. By using the optical tubes of the two scopes, one could remount them to point at each other. Placing the film inbetween, one could focus both scopes on the grain of the film. By then placing a light source at one scope's eyepiece, the other scope could had the detector placed there micrometer or threaded rod stage could be used to hold the film and allow the movement of the film. Combine with the stepper motor for stage movement, and the sound card for data aquisition. Then extract data from the wav file and export into graphing/stats software. This type of design actually is pretty close to a commercial microdensitometer design.
     
  20. Photo Engineer

    Photo Engineer Subscriber

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    Kirk, what I have at present are 2 4x5 Kodak definition targets. One is positive and one is negative.

    I can try to duplicate these onto film, but I am not sure that the duplicated quality would be satisfactory using my equipment. Not sure, but if you think so, suggest a film and developer and I'll give it a try.

    PE
     
  21. Tom Hoskinson

    Tom Hoskinson Member

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    Yes, chromium on glass and somewhere I have some dupes we made on Tech Pan and developed in D-19 that are pretty good. BTW, I have a lot of 70mm perf'd Tech Pan in the freezer - don't know how good it is anymore...

    The Edmunds chromium on glass USAF target and/or Stouffer step wedge targets would provide common and easily available starting points for comparison. Excellent suggestion.

    You're right, Kirk. With the line scan stuff my head was off in the world of HVTEM analysis - sorry!

    With regard to image processing S/W, according to one of my colleagues there are Linux S/W routines that will do the job.

    However, what we use (to process SEM, TEM and Xray and optical microscopy images) is a site licensed MediaCybernetics product called Image Pro Plus. This software is currently only available for IBM PC type hardware.

    There is considerable "sticker shock" associated with Image Pro. The "light" version costs just under $1000.00. However, many Universities and Companies have bought site licenses.

    ----------------------------------------

    Media Cybernetics Image Pro Plus

    http://www.mediacy.com/index.aspx?page=IPPRequirements

    Media Cybernetics Image Pro Express (Light Version of Image Pro Plus)

    http://www.mediacy.com/index.aspx?page=IPEFeatures


    Operating System Computer RAM Storage Other
    Windows® 2000 500 MHz 256MB 10 GB* Service Pack 4
    Windows® XP Pro 750 MHz 512MB 10 GB* Service Pack 1
    *Suggested storage size for large images files generated by advanced cameras.

    Spatial Measurements
    • New snap feature allows you to automatically save measurements into images for documentation
    • New scale bar for X and Y measurements can be placed on your image as an overlay
    • Measure co-localization of probes in separate gray scale images or within a color image
    • Work with weighted centroid, clumpiness, heterogeneity, min/max density, dendrite length, end point, fractal dimension, margination, and additional perimeter measurements
    • Record Pass/Fail routines in a macro and play back when needed
    • Measure best-fit line, arc, and circle with metrology tools
    • Outline objects automatically with Auto-Trace feature
    • Measure lengths, areas, perimeters, and angles
    • Calculate max, min and average thickness between lines
    • Use the Caliper Tool for edge detection and measurement

    Image Analysis
    • Visualize image data with scattergrams, histograms, and line profiles
    • Display image intensity values in a 3D Plot with Surface Plot
    • Collect data from multiple images with Data Collector
    • Calculate straight line, circle, irregular line, or area histograms
    • Use new thickness measurement options
    • Analyze percent area of multiple threshold levels
    • Define and manage multiple areas of interest (AOI) in a single image
     
  22. gainer

    gainer Subscriber

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    It's been a long time and I have had an attack of encephalitis in the meantime, but I found a catalog of Circuit Specialists from 1998. If they are still around, they are at www.cir.com. You will want a meter with LED readout rather than LCD. They are cheap for 3 1/2 digits, which will do quite well for this purpose. Who measures densities above 19.99?

    My enlarger uses an 82 volt bulb, obtaining that from half wave rectification without filtering. I have been laying off for some time to build a regulated DC supply for it. For most of my uses I can put up with small fluctuations, so I keep putting it off.
     
  23. gainer

    gainer Subscriber

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    I forgot to address the question of serial output. These panel meters are essentially timers that count the number of time increments it takes to integrate a step inut until the signal voltage equals the integral. I don't think any of them will have a point where the serial or even parallel digital output is available. the whole circuit is integrated and provides out put directly into a 7 segment display.

    I know there are available integrated A-D converters, and if you are using the simple log amplifier circuit its output will be the analog input for the A-D converter as well as the panel meter..
     
  24. noseoil

    noseoil Member

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    Sorry to be so pedestrian in this discussion, but the film and developer come into play at some point. Once this device for measuring has been created, I will be very interested in seeing which film-developer combination ranks "first". Too many variables to list, too many films and developers, I know, but it will be interesting to see how the latest offering in tabular grain film rates against the old efke 100 or tri-x. Hopefully such a list will be possible. tim
     
  25. df cardwell

    df cardwell Subscriber

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    This is kind of interesting. And goodness knows I like to watch ANYBODY work.

    I understand this is taking place in the APUG Province of The Back of Beyond, somewhere behind the smokehouse.

    But I'd love to examine the premise of this exercise and how it relates to taking pictures and hanging them on the wall.

    The over Gratuitous Technicalisation of Silver Based Imaging has been a concern of mine for a long time. I fear there is a great danger that, said and done, the Test will simply Test the Testers rather than the intended process.

    I appreciate the apparently 'seat of the pants testing' protocol used by garden variety photographers [of imaging a contrasty target of known contrasts and dimensions for viewing] suggests the potential for error. I also acknowledge that it may be desirable to achieve more detailed information.

    At the same time, I DO wonder what that higher layer of resolution this discussion hopes to achieve.

    Of possibly more relevence, does the process suggest a protocol so refined that it will be unrepeatable and hence yield invalid results ?

    In particular I'm concerned that the results will have micro-resolution that has less relevence to image - making than our current slap-dash protocols.
     
  26. Tom Hoskinson

    Tom Hoskinson Member

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    One of my rules is that the testing protocols must be repeatable and capable of generalization. These may prove to be unrealizable goals. If so, that is an answer - of sorts.

    Yep, that's always a possibility. But hopefully the results will lead to better understanding and predictability of the process.