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John Garner
04-19-2012, 10:09 PM
Good Evening, All --

Can anyone suggest a readily-available software system that either superimposes or rapidly alternates between two very similar images -- preferably allowing at least one of the images to be zoomed and rotated in plane to more-closely correspond with the other -- to make differences easier to spot?

I'm somewhat expecting to be asked to evaluate the configuration of a specialized bracket (about the size of a one-pound box of graham crackers), in situ (and thus no CMM or surface-table measurements) from digital "snapshots" taken half a world away. I'd like to compare them to similar photos of a known-good bracket, which I can have taken here.

Thanks in advance for your suggestions.

John

armedandsafe
04-19-2012, 10:32 PM
I can think of several methods to use, but would like to know what software you already have (if any.) It is not a tough project, but is done differently on different software.

If you are looking for a cosmetic comparison, that is very simple. Make a blank canvas in your editor, stick both pictures on that canvas (think collage) and you are done. For scientific or measurment comparison, things get a bit more complicated. At least, make sure that some known measurement is included in the picture. Not a coin, but a rule of some type.

Pops

John Garner
04-20-2012, 12:24 AM
armedandsafe --

My office computer has the Microsoft Office suite, a couple of proprietary document-archiving-and-retrieval programs, and the "big three" web browsers, and I could in theory commandeer machines with Pro Engineer, GSI V-Stars, and SpatialMetrix Insight . . . although it's literally been years since I used one of those last three programs.

Although I'd love to be able to do some form of computer-based stereo photogrammetry, that's probably not in the cards for now. Under the circumstances, I'll be happy to point to pictures and say "The bumped bracket is bent right here." or "I don't see any bends or dents."

John

elf
04-20-2012, 12:44 AM
Another option is to create a synthetic 3-D image using Zerene Stacker. It's primarily a focus stacking program, but can also create 3-D images. Here's the link: http://zerenesystems.com/cms/stacker/docs/syntheticstereo These 3-D images give a lot more context (for want of a better word) to the image detail.

p.s. Just a satisfied user of the software

armedandsafe
04-20-2012, 12:54 AM
armedandsafe --

My office computer has the Microsoft Office suite, a couple of proprietary document-archiving-and-retrieval programs, and the "big three" web browsers, and I could in theory commandeer machines with Pro Engineer, GSI V-Stars, and SpatialMetrix Insight . . . although it's literally been years since I used one of those last three programs.

Although I'd love to be able to do some form of computer-based stereo photogrammetry, that's probably not in the cards for now. Under the circumstances, I'll be happy to point to pictures and say "The bumped bracket is bent right here." or "I don't see any bends or dents."

John

If this is the only time you will be doing this, I would recommend you find a friend or associate with PhotoShop or GIMP and buy a 6 pack. ;)

PowerPoint or Publisher will allow you to get the two pictures on the same page, or seperate pages to show two-up, or flip back and forth. I don't think either of those will allow you to overlay one on top of the other.

Getting the two pictures on the same page is not hard and will probably give you the information you need. One thing to watch is that your local picture is taken from the same angle as those you receive from far away. Have the distant photographer take a number of pictures and then use those to steer your pictures.

Another approach would be to set up your computer and the faraway computer for 'net meeting, using voip and a web cam on each of them. This might not be possible or practical. "teamviewer 7" is a program which my nerdly daughter uses and it is free. She was head tech at ITT Institute for a number of years and never managed to break it.

It is a little hard to give you very specific advise without knowing the item you are examining. Comparing the bracket to hold a Saturn Rocket during power-up is somewhat different from comparing angle brackets on a lift bucket. :D

If I were commissioned to take this project, I would insist on having communications with the photographer while pictures were being taken, that both still and video shots were taken and that I would be able to request more pictures later (from a different angle, different lighting, clean off the oil'n'muck, etc,) Then again, perhaps this is not such an important part that one should take such care with it. If replacement is $500 and the examination and photographing is $5,000, the decision is easy.

Pops

Joel
04-20-2012, 01:01 AM
Photoshop, paint shop or whatever should work fine. Reduce the transparency of your good bracket and superimpose the image over the questionable one as a layer. Zoom and rotate are obviously not a problem.

dp
04-20-2012, 01:36 AM
http://www.downloadroute.com/PhotoComparer-Christos-Prevezas-Software.html

Evan
04-20-2012, 01:40 AM
As Joel says, the software is not an issue. Any software with layer capability will do. The real problem is to take the pictures at precisely the same relative position in 3 space. That means exactly the same in all six locations of pitch, roll, yaw and the three translation axes. If any are out by even a little it will be very difficult to match the images even using software adjustments.

For instance, if the distance is different you can't fix that just by zooming because the perspective angle will change too. The closer the camera to the target the more severe this becomes. For a closeup of a part it will matter a lot. These problems can be reduced by using long shots with a telephoto lens and a very narrow field of view, if possible.

Regardless of the lens you use when taking macro shots and distances of less than a few feet there are several distortions that come into play and they vary a lot as the position of the camera changes. I have dealt with this range of problems for many years as I used to do image retouching professionally.

Try it yourself by taking a series of photos from slightly different distances and angles and see how difficult it will be to do what you require. It is a technique that I use frequently except that I don't use a blink comparator.

Instead, I cross my eyes in the same manner as viewing a crossed eye stereo pair. I learned to do that as a child to figure out the "What's different in these pictures" puzzles. It works as well or better than blinking the images. The difference stands out instantly.

ikdor
04-20-2012, 04:10 AM
You can make a picture transparent in Powerpoint:
Drop background picture on slide.
Draw a rectangle, fill with a second picture instead of a color and set transparency.
You can even rotate and scale the picture using the controls for the rectangle.

Igor

demerrill
04-20-2012, 10:50 AM
'Blink comparator' is a means commonly used in astronomy to aid in detection of celestial objects that move or change brightness. I haven't personally used any of the available software but here is a Google search which indicates that it exists:
http://www.google.com/#q=%22blink%20comparator%22%20software&nfpr=1&ei=xHSRT4SwEMTy6QHem_WyBA&sqi=2&start=0&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=98f6d9d2e4b0df84

Let us know if you find that one of these works for your application of detecting changes in shape.

David Merrill

demerrill
04-20-2012, 11:33 AM
I got curious and verified that the free download, IrfanView, will do this well. See the comments at the following site for instructions.

http://www.instructables.com/id/Blink-Comparator-on-Personal-Computer/

David Merrill

John Garner
04-21-2012, 01:27 AM
I extend my sincere thanks to those who offered comments and suggestions on this matter. Today's executive decision, that the folks on site can make the fly-or-not decision, gives me time to explore the techniques and software you've suggested without hurry-up-and-decide pressure from those who won't look beyond performance to schedule.

Again, thank you very much for your time and consideration.

John