I have a modified camera to capture NIR images. In the last events, I have been experienced a systematic problem. All the pics taken appear not proper to use in NDVI analysis - the top right corner always return low values of NDVI (fig. 2).
Follow some of my examples: The first image is a NIR-raw (fig. 1). The second, is a NDVI image processed using ArcMaps software (fig. 2).
Ps: This problem happens independent of the hour of day, excluding the possibility of shading.
Does anyone has a suggestion for this issue?
Thank you very much!
Fig 1. NIR-raw image.
Fig 1. NDVI image.
The color gradient in the photos taken by your modified camera seems to be the cause of the artifacts in your NDVI image. To determine whether this is due to the camera or to the ambient lighting, take a new photo that shows the gradient and then rotate the camera 90° and take another photo of the same scene.
I suspect the artifact is due to the camera. Did you buy Rosco #2007 filter from Public Lab, cut a small piece and install it in the web cam? In front of the lens or behind the lens? If so, I suspect the piece of filter is not perfectly flat and perpendicular to the optical path. If you adjust the filter the problem could be fixed.
Did you also buy some red filter? Red filter sometimes works better with the little CMOS sensors in web cams.
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