Public Lab Research note


NIR, Rosco fire #19 and my elph 300HS from Christmas

by admaltais | August 15, 2015 03:35 | 2,064 views | 1 comments | #12145 | 2,064 views | 1 comments | #12145 15 Aug 03:35

Read more: stable.publiclab.org/n/12145


What I want to do

Monitoring crops

My attempt and results

Replacing the original filter in my elph 300HS by the Rosco Fire Filter. Great, the opening is quite easy, the old filter has been removed, the new fit perfectly in place, everything is closed, everything is sealed, CHDK and all...!

Ok test! Well, it is pink-red, only pink-red! Not the splendid blue-orange as we can see on the beautiful photos on infragram website, no, just pink-red! Here the NIR photo along with the useless NDVI version (NDVIBlu2RedWB.lut) Ok, that was not the real Rosco filter from the Infragram kit (Roscolux Fire #19), it's only a flash gel, one from the package of the "artistic picture fun", this one: E-Colour #019: Fire. But it's still a Rosco Fire #19!

Questions and next steps

Is it possible that there would be some small difference between the filters? Does it have to be exactly the one sold in the kit? On the Infragram.org sandbox app, do I just need to put my jpg or raw image or I need to do something before with any image software?

Thanks a lot *The Infragram kit is on the way!

Cheers from Montréal Alex

subway.JPG

NDVI.jpg


1 Comments

Alex, The two filters are probably the same. The #19 filter will work best if the you do a custom white balance on the camera before you take photos. Flood the sensor with red light while doing the custom white balance (FuncSet/WhiteBalance/Custom) e.g., by pointing at red paper in direct sunlight. Photos of healthy foliage will then be turquoise, and the NDVI values will be closer to where they should be and have more range.
Chris

subwayNDVI.JPG

To make the NDVI image above, both histograms were stretched and 20 was added to the NDVI values (digital number) to put them closer to the right range.

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