Hello all,
I have assembled a Mobius camera with Public Lab's infrared lens, have focused the lens, and went outside to take some pictures. It is autumn, so many of the plants are more orange than green, but the trees still had a fair share of green on them.
However, when I upload the images to http://www.infragram.org I am not achieving the results that I expected. Are my expectations erroneous? Other opportunities for failure were:
- The assembly
- The config file
- The plants not being green enough
- A processing glitch
- Who knows
Here is the base image that I have taken, without any digital editing.
This image is of course taken using the public lab NDVI lens installed into the mobius camera.
When I upload it to www.infragram.org and choose the basic present for the NDVI red filter images, I am returned a mostly black screen:
When I ask infragram.org to return a colorized analysis instead of a basic one, the analysis is still a bit strange:
Does anyone know what needs to be changed here so that I can get better photos? Does anything at all need to be changed? Please help out!
Abdul,
You are correct that all of the things you list could be responsible for the failure to produce a meaningful NDVI image. It could also be due to the color of the ambient light being strange, or the custom white balance being wrong for that lens. Without some controlled tests it will be difficult to determine what is to blame.
The photo from the camera is not blue enough to be directly converted to NDVI (i.e., with the standard formula). The blue channel, which is used for NIR, is not much brighter than the red channel in pixels capturing green leaves. If you alter the photo by making it bluer, stretch both histograms, and then increase the value in all the pixels of the NDVI image by 15, you get this:
Making photos which can be converted directly to a facsimile of NDVI requires a custom white balance appropriate for the lens, the sensor, and the ambient light. It also requires a properly exposed photo. Satisfying all of these requirements for each photo taken of plants is probably not possible if the same white balance and automatic exposure are used for all photos regardless of ambient light.
Chris
Reply to this comment...
Log in to comment