What I want to do
Change external filter on A490 from Rosco 2007 to Wratten 25. Try it for NDVI.
My attempt and results
Photos of conversion and finished change: filter material:
A490 with external filter:
First testing image examples, were shot after custom white balance in shade using red file folder:
Test photos of the community garden at Asbury United Methodist church in Livermore CA.
as shot:
processed with Ned Horning Fiji tool:
processed with Infragram web tool:
Additional test images show comparable NDVI images in my front yard, shot with Rosco 2007, with improved white balance, and the new Wratten 25 filter; processed with Ned Horning tool with the Chris Fasti lut.
Rosco 2007, with improved white balance:
new Wratten 25 filter:
Questions and next steps
Tune white balance or other parameters to improve results.
Why I'm interested
Continue to explore as tool to assess vegetative health.
6 Comments
Nicely done. I love the old beat up Kodak packages (but check out this one). Did you get it on eBay? How much? You must have a lot left over for doing internal conversions.
It's probably okay to white balance in direct sunlight, because the more red the better. But your photo looks good. Here is the histogram. Good separation of blue (NIR) and red:
I think you processed the Wratten image like an infrablue image. Here is an NDVI image using the blue channel for NIR and red for red:
Infragram.org does not have an easy way to process Wratten 25 (SuperRed?) photos. I couldn't figure out how to do it at the new and improved Infragram sandbox.
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Thanks Chris, I'll try to tick through your points, so the discussion is available for all.
Got it on E-bay for $9.99. Yes, I do have lots left for other conversions. As I cut it with scissors, trying to avoid fingerprints, I also realized I don't have a feel for how vulnerable the material is to scratches and handling problems. I'd be more comfortable with it mounted internally, to avoid handling scuffs.
Based on your experience with both, would you go with this Wratten 25 over the Schott glass filter you got us, to convert an A1200 with internal filter?
For a Rasberry Pi noir camera, I recall Mathew Lippincott posted a glue technique he's used. I need to check that. Some of the trimmed pieces may be large enough for that purpose.
How do you get the histogram you show? In PS, I see a number of other views, but not that one.
Another remedial question: Yes, I guess I just processed the Wratten image like an infrablue image using Ned's tool. What is the workflow you use to to use the blue channel for NIR and red for red? Does it scale to a directory of images. I've had trouble, and see others have too, with PS actions on multiple images.
For infragram.org, I've missed some calls. Is an easy way to process Wratten 25 (SuperRed?) photos a topic under discussion?
Thanks for all your work in this area!
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