Hello everybody. I really appreciate this useful and open-minded communtiy. I spent the last couple weeks reading many articles on NDVI photography and made some great progress with all the information provided on this site. Now I'm at a point at which I need some specific help from experts.
What I want to do
I'd like to make a big NDVI Map with my quadrocopter. The Idea is to support the farmers around me with useful information.
My attempt and results
I did make some progess with a proper white balancing and re-focusing the mobius action Cam. I managed to produce relatively accurate NDVI photos with the Infragram Sandbox-Tool and a custom HSV-Setting. The H-Value is [-(R-B)/(R+B)*4] ; S=V=1. You can see these results in the attachement.
Questions
Even though I've got some good results with the Infragram Sandbox, the resolution of my images gets really decreased. So I installed Ned Hornings PhotoMonitoring Plugin on Fiji to get the same result but with a much better resolution. Unfortunately I'm not able to reproduce these results. I can't include my custom HSV-Formula i used on the sandbox. I'm also not sure which .lut file and ColorIndex values I have to use to get the same results like on the sandbox. The best approximation i got is in the attachement.
Additionally I can't understand why in my picture with the sandbox high photosynthesis areas are gree represented and not red. I would be really thankful if somebody can support me.
Thanks.
Here you can see the scenery (taken with an iPhone).
Here is the picture I get in he plugin with the questioned settings.
A quick follow up question: The defautl .lut in the infragram sandbox is the following i think.
Even tough a high NDVI value (red) represents high photosyntesis, it does exactly the opposite in my picture. green is high photosynthesis and blue/red is low as you can see. Why is that?
10 Comments
Hi Silvanhi,
That's a gorgeous landscape. And a great subject for ndvi images. There are a couple of things I don't understand about your results.
If you include one of the super-red photos from your Wratten 25A Mobius, we might be able to do better troubleshooting.
In Fiji, right after you produce an NDVI image, if you add about 25 to the value in each pixel (process/math/add) you can slide all the colors in the NDVI image to the right on the NDVI color scale. If you have to do that to get an NDVI image that is meaningful, then the super-red photo from the Mobius might need a different white balance setting for that type of scene.
Chris
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Hi Chris, Thanks for your fast answer.
1.) Here is the infraBlueNDVI.lut; I think its quite the same as the NDVIBlu2red.lut
2.) Ok. I use from now on the NDVIBlu2red.lut in the Fiji app. What do you mean by not having magenta in it? How can it be that an InfragramSandbox image with the NDVIBlu2red.lut Color Key does produce magenta? The only possible answer is that the HSV-formula [-(R-B)/(R+B)*4] ; S=V=1 ; does that. I'm a bit confused since the NDVI it produces does quite a good job representing high/low photosynthesis areas.
3.) thanks for your thoughts on that.
Here is my original superred photo taken with Mobius and Wratten 25a filter:
I processed this foto in PhotoMonitoring with the NDVIBlu2red.lut and added afterwards a value of 40 to it. now it looks like that: 99_-1_1_40.tiff
Do you think it represents good NDVI values? There are quite a few questionmarks e.g. if you look at the small house at the lower left corner. The wall is red in the NDVI which represents a high NDVI value. But there is no photosynthesis on that. Even tough I have to say that it is painted dark-greenish. Can I improve things like that? An other example would be the tree trunk. It is also red but doesnt make any photosynthesis.
Here are my white balancing settings for the Mobius. I did over one hundred trial-and-error-tests to get the best possible values with the InfragramSandbox and the upper HSV formula. Do I have to make the same tests again with the fiji app?
Silvan
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