canon S110 - which is the best filter?

[netp...@gmail.com]

HI all,

I am in a little trouble:
I replaced the stock IR filter on my Canon S110 with the redish foil I got from Publiclabs and did the calibration with the red paper.
The result can be seen here: http://www.infragram.org/i/554b6123d9c0358308000245

Now I am a little puzzled as the NDVI of the leaves is around 0.3 which is pretty low for a well fed plant in spring. Isn't it?

Should have I chosen the blueish foil?
thanks in advance!
Tom

[Chris Fastie]

Tom,

The red filter is a good choice. Your calibration seems to have done a good job. The leaves in your photo are a little overexposed, so there is not much difference between the values in the blue (NIR) and red channels -- both blue and red are very high. The leaves in the shade produce reasonable NDVI values, but still a little too low.

In photos taken with a red filter, healthy foliage should have a deep turquoise color when the white balance and exposure are proper for NDVI. The NDVI image above was made with Ned's Fiji plugin which allows the red and blue histograms of the original photo to be stretched which helps amplify NDVI.

Chris