Late last year we released our first version NDVI converted cameras using Schott BG3 filters. Using those filters we were able to generate pseudo NDVI images with a single camera, building off the work of the Public Lab project. After working with faculty at the University of Boston and the MEASA Lab at KSU, we determined that we weren’t quite getting the best results possible with the BG3 filter glass. Unfortunately, no off the shelf filter glass seemed to do exactly what we needed, block out red light and allow NIR light to pass instead. Luckily, we were able to find a manufacturer to help us build a custom filter to our specifications, and the results are looking really good! Below are two images, the first taken by a camera with BG3 filter glass and the second taken by a camera with the new custom glass, the difference is clear.
BG3 Filter Glass
Custom Filter Glass
Aside from higher overall values, there is more differentiation and detail in the leaves and a larger difference compared to the non-organic background material. This is especially important for this type of camera. Since these are uncalibrated, pseudo NDVI images, what is really needed most is high differentiation so that comparisons can be made between the majority of plants and potential problem areas. The higher detail available now makes it possible to catch unhealthy plants sooner.
Custom Filter Transmittance vs Wavelength
The new filters will be priced at $39.99 for the filter alone (8.9×7.9mm, fits SX260 and S100 at least, potentially others) and$499.90 for a ready to go converted SX260 with CHDK. It’s a little cold to be doing any crop surveys here in the Northeastern US right now, I actually ended up killing those two plants after taking them outside for just a few seconds! We’ll be out and collecting imagery as soon as anything starts growing and I’ll post updates as they become available.
Comments
Hi Jeff, I write you from Argentina and I`m discovering in this moment this blog very interesting. I’ve read it, and I have a question to you about this that I can’t understand. In order to reach the NDVI index, don’t we need a transmitance specifically in the wavelength of red (630-690 nm)?. I’m needing a filter to convert a Canon S110 in order to obtain accurate graphics of NDVI, but this graphic of transmittance is confusing me. If you could help me about this, I’m very grateful. Best regards, Gonzalo
Some issues, first, the cameras are consumer grade, with consumer grade imaging sensors(a lot of bad pixels). An upgrade to a Grade 2 imaging sensor would make a marked improvement in image quality and performance.
Second, images taken with a silicon sensor, that are consumer grade, with the addition of a cut filter will get the results you have.
Third, the camera lenses in these cameras are not made for transmission outside the visible. They work, but not nearly as well as lenses designed for high transmission, no vignetting, MTF, Distortion, field curvature, with built in removable filter holders.
Spectral analysis would be problematic no matter the software.
Can you share some photos taken with the new filter?
This is their spectral graph without a notch filter:
This is with the notch filter:
Doesn't look like a massive amount of difference except the price of importing it to the UK makes the maxmax more expensive.
James, it is definitely a different filter as ours was custom made and I'm sure theirs was as well. There is a slight difference you can see visually between the two images (on theirs, vegetation looks more orange) but I'm not sure exactly what the transmittance values on their filter are. I don't have a side by side unfortunately.
Great work, it would be interesting to see how this compares to the maxmax conversion. I would have thought they were very similar although the filter may be different as it would also likely be a custom build.
Do you have any direct comparisons with maxmax?
Great! I'll be working on speeding them up and making them work with any picture format/size.
Nice, I've been following your work. Yesterday I received the new filters, they look really different from the old blue ones. I am looking foward to test it. Also I will try Fiji, Agpixel and any other options to generate ndvi and biomass.
Would be really nice if you share your scripts. Once again congratulations for this development and research. For sure this will be a great and cheap option for agricultural remote sensing.
@Photofly The filter can be used for any camera that it fits into.. so far we've only verified the Canon SX260 and S100. More point and shoots probably will work, but it's impossible to tell until you open it up and verify it physically.
@Arnaldo Thanks! I actually use my own scripts to generate NDVI because Fiji wasn't giving me the scale and I was also sometimes suspicious about what was really going on inside. Plus I wanted the ability to mess with other experimental indices more easily. I have a bunch of AWS credit so I might put it up so others can use it easily as well.
Wich software you are using to do the NDVI scale?
Best Regards and great Job!
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