NDVI Filter

[Ed Blanchard]

I have been experimenting using a Rosco #19 Fire Red Filter on a Yi action camera.

Its working OK but I am having a lot of trouble getting the custom white balance correct.

I was searching through the Public Labs Archive and came across Orange is the new red written by Chris Fastie in 2015.

What interested me was the comment by CHUMBA and Chris about the Rosco E116 Medium Blue Green filter not needing a custom white balance.

Is anybody using this filter ?

[Chris Fastie]

Hi Ed,

I have not heard of anyone else using the E116 filter. If you leave a comment on that note, CHUMBA should be notified and maybe he can report on his experience.

I have noticed a few cases where blue filters produced photos which could be converted directly to a facsimile of NDVI even though a custom white balance was not used. Blue filters are harder to make compared to red filters because they must block red light but pass colors on both sites of red (blue and NIR). Red filters just block one end of the spectrum. So different types of blue filters are not all created equal, and for our use they produce various mixtures of NIR and visible light in the red and blue channels. Some of them produce reasonable NDVI using a preset white balance (cloudy or sunny) and some produce photos that resemble false color IR satellite images. Others require a custom white balance to get good looking results. 

If good looking results is your goal, then a blue filter might be called for. But red filters will generally produce a purer NIR signal in the blue channel and using red for the visible information is generally better than using blue. Red filters seem to require a custom white balance to produce photos which can be converted directly to a facsimile of NDVI.

Does the Yi camera have the ability to make a custom white balance? If so (and if it works like a PowerShot), it might be worth trying some deep red or purple paper in direct sunlight for the custom white balance procedure. Or maybe the Bayer filter is that camera is different and some other color is required.

Chris