Canon IXUS 240 HS - feedback on modification

[LgsPaul]

Hi everyone,

I have recently modified a Canon IXUS 240 HS camera (ELPH 320 HS).

I used the red filter provided in the Infragram Filter kit and did the WB calibration.

I have some questions/remarks regarding the modification and would appreciate an expert's input :) :

- It is still unclear to me what a good result should look like. Is it possible to have some general feedback based on the provided pictures ?

- Some non-vegetal pixels have a NDVI value that is almost the same as the vegetation (the table at the bottom of the example picture). Is this expected ?

- The right hand of pictures tend to be a little blurry, I suspect it comes from of the screws on the back of the sensor.

(also, I uploaded the picture on http://infragram.org/i/5551be1bd9c0358308000272 but cannot access it anymore because of a js error. I'm looking into it)

Thanks a lot for your help !

Paul

[Chris Fastie]

Hi Paul,

That looks like a pretty good red-filtered photo. Here is the NDVI result you should get from that photo without any manipulation and without histogram stretching (made with Fiji).

The NDVI values are low because there is not enough difference between the blue and red channels in the original photo. Healthy plants in a red-filtered photo should have a rich turquoise color like this:

The color is influenced strongly by the custom white balance, but also by the lighting and exposure of the photo. Custom white balance should be done while flooding the sensor with red light (red paper in direct sunlight). Over or under exposure changes the relationship between the red and blue channels (they become more similar to each other). Some practice is required to get meaningful NDVI results.

Chris