Imaging and stitching across a grid - entomology collections

Discussion forum for techniques and issues relating to the creation of panoramic and/or "mosaic" images

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apgdowling
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Joined: Tue Jun 25, 2013 10:51 am

Imaging and stitching across a grid - entomology collections

Post by apgdowling » Tue Jun 25, 2013 11:12 am

Hi Everyone,
I am at a small museum and I am trying to develop a system that will image an entire drawer of insect specimens (41.5 x 48.5 cm). This has been done before using several strategies, but none are just right for my needs. Gigapan is the least expensive of the methods used by other museums, but the stitched image suffers from parallax issues. Another system developed in the UK uses an X/Y rail system above the drawer and the camera is controlled by the computer to systematically work its way back and forth across the drawer until all images (usually about 250+ images) are taken and then it stitches them together. This system uses a telecentric lens so there is great depth of field and no parallax problems. I would use this system except for the fact that they charge >$120,000 for the system including delivery and setup to the US. Way out of the price range for a small museum. Moving a camera on rails is nothing new to photography, nor is stitching together a mosaic of images. What I'm trying to determine is if there is available software to automate these processes. Is there an inexpensive way to create my own system (for something like $20,000) with camera and rails all controlled by a computer? We have 1800 drawers to image and at 250+ images to adequately cover the drawer, we don't have the manpower to have a person snap each picture and then move the camera to the next location. Maybe this sort of system should cost $120K+ but too often things made for the science world suffer huge markups. It just seems like there should be a better, less expensive way to accomplish this task. Any advice from the community would be greatly appreciated.
Thanks
Ashley

dsp
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Joined: Tue Feb 20, 2007 11:09 am
Location: Hoboken, NJ

Re: Imaging and stitching across a grid - entomology collect

Post by dsp » Tue Jun 25, 2013 5:57 pm

This should be relatively straight forward to do as a DIY project IF you have someone that knows a little programming. You would buy something like the multiple axis system that is on this page (I have never used this particular manufacturer, so list it only as a representative system) http://www.lm76.com/screw_driven_slides.htm. The guides would be positioned by a stepper or servo motor. I personally like steppers for this kind of application, and there are many cheap solutions (http://www.automationdirect.com/adc/Ove ... er_Systems , http://www.omega.com/prodinfo/stepper_motors.html , http://www.phidgets.com/docs/Stepper_Mo ... ler_Primer ), and mount the whole rig on a frame made of aluminum channel like 80/20 (http://www.8020.net/). The stepper motors can be controlled via serial or USB, and then you need to have a camera that can be triggered by computer as well. Many cameras have had their trigger reverse engineered, so you just need to find out what it is for your camera, and connect to the external remote input. You would program the rig to move in a grid, and take a picture at each location. What you don't get in this, but I hope you get in the professional solution, is a tight interfacing, to be sure that an image was taken at that grid position, etc. It could be coded in in some hacked ways too, for instance by checking the number of files in the directory, or the like.

The 80/20 will be a couple hundred at most, the two steppers + controllers likely under .5K, perhaps much cheaper, with the linear slides the most expensive part (neglecting human cost). I would think there have been similar projects built elsewhere, and the cross slides are used in timelapse photography on rails, so I imagine there is a lot of info out there. See http://www.davidhunt.ie/?p=2822&page=1 for instance. I wouldn't use a belt driven guide for a more serious project, just because I like the positive action of a lead screw slide, and you can hold a big load. But these projects are very similar to what you want...
cheers, dsp

Jim Zuccaro
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Re: Imaging and stitching across a grid - entomology collect

Post by Jim Zuccaro » Tue Jun 25, 2013 10:42 pm

I'll add an idea to what Darcy wrote; there are inexpensive CNC woodworking routers and inexpensive CNC metal milling machines that are sold for home hobby use. They are bridge type machines that are large enough for your drawer. A "table top" CNC wood router, with a high-speed spindle and computer controller, 24" x 36" x 6" envelope is available for $7,000 or less. If you didn't buy a spindle, the router motor part, that would reduce the price. The operating programming is current industry used programming. The positioning precision is hundredths of a millimeter.

Camera shutter controllers are available in many forms. For the time duration needed to photograph a drawer with 250 photos, a no-feedback time-lapse interval timer would work. The movement rate control of the table-top router is very consistent.

Max could say if scripting could be used in PTAssembler to set-up each mosaic stitching project for the programmed photo raster that was be used to take the pictures. For batch processing of projects, it might help to prevent a bad or missing image in one project from 'hanging' the whole process.

apgdowling
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Joined: Tue Jun 25, 2013 10:51 am

Re: Imaging and stitching across a grid - entomology collect

Post by apgdowling » Sat Jun 29, 2013 12:34 pm

Great, thank you for the helpful replies. I believe this is something I can achieve based on you recommendations with a much lower price tag than the units currently sold. If I go forward with this and come up with an actual working unit, I'll post and let everyone know how it went.
Thanks again for your help.

elf
Posts: 221
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Re: Imaging and stitching across a grid - entomology collect

Post by elf » Tue Jul 02, 2013 2:57 am

This thread in the LargeFormatPhotography forum could be useful.

I'd recommend posting your questions on this forum as there are quite a few macro (and insect) specialists there. My own automated desktop setup is here, but it is designed to do spherical instead of orthographic stitches.

This CNC router looks like it would make an excellent starting point and they also have a DIY machine detailed here.

Consider shooting at a higher magnification and focus stacking to capture more detail.

dsp
Posts: 586
Joined: Tue Feb 20, 2007 11:09 am
Location: Hoboken, NJ

Re: Imaging and stitching across a grid - entomology collect

Post by dsp » Tue Jul 02, 2013 9:44 am

Definitely would want a diffuse light source/box, and I would put a ring light around your macro lens as well. I would think about using a machine vision/telecentric lens so that defocus doens't change magnification/etc. BTW, what is final res you hope for, in terms of pixels per inch of real object, or alternatively, pixels per "drawer"?
cheers, dsp

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