If I use the Blue filter, why do the plants come out yellow-ish looking? If I use the Red filter,...
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Blueish photos result when the blue channel is brighter than the other channels. Reddish or orangeish photos result when the red channel is brighter than the other channels. If the subject reflects lots of NIR, then the channel capturing NIR will be brightest. If a custom white balance has been done to facilitate NDVI, the channel capturing NIR will be even brighter.