NDVI Testing Continued – sx230 CMOS Sensor and Lighting

NDVI Testing Continued – sx230 CMOS Sensor and Lighting

Below are a couple simple test results conducted to compare the effect of various camera settings, lighting conditions and white balance settings on NDVI results with a Canon sx230.

Details on the Single Camera NDVI effort are explained here: http://flightriot.com/vegetation-mapping-ndvi/

The Canon sx230 has a CMOS sensor and seems to pose more challenges in creating NDVI than CCD sensor cameras such as the A490 adn A810. It appears that the sx230 provides more dynamic NDVI outputs in lower light conditions.

An Apollo #4400 filter was placed on the outside of the lens using tape.

All images were captured indoors, mid-day, with White Balance set manually prior to each shot using:

  • a stack of white copy paper in most images
  • a blue file folder as reference test
  • a blue binder  as reference test

The white card used was captured in the photos.

Camera color settings were set to “Off”,  “Vivid”, and “Custom Color”. The images with Custom Color settings are represented by the files that start with sx230_440_Indoor_… Here are the Custom Color settings used:

SCALE —|       |       |       |       |—

Contrast                  X

Sharpness               X

Saturation                              X

R                                                 X

G, & B                       X

Skin                                           X

I used these settings to get better NDVI value range but I don’t know that this is a good idea. Ultimately any camera selected will need to be calibrated to some ground truth value.

The following settings were used in the Fiji/ImageJ Photo Monitoring Plugin:

PM_Plug_NoStretch

Color Scheme used: Blue=Lowest NDVI values, Magenta=Highest NDVI valuesColorTable

 

 

 

The following gallery images were taken indoors next to a large window with SUNNY conditions outside, lit with indirect natural light. The Camera color settings were adjusted to create different NDVI results. Hover over any picture to see the settings used or click on any picture to launch the gallery view.

The following gallery images were taken indoors next to a large window with RAINY conditions outside, lit with indirect natural light. The Camera color settings were adjusted to create different NDVI results. Hover over any picture to see the settings used or click on any picture to launch the gallery view.

5 Comments

  1. MegaFlare

    Are you getting good results with taping the filters to the outside of the lens as opposed to installing inside the camera?

    • geobduffy

      As far as I can tell I am getting similar results whether the filter is mounted on the outside or inside but I will place the filter internally once I decide on best filter for a specific camera. Although it does add a nice protective cover to the actual lens when on the outside… I think there will be a range of filter options that will work well, especially for the CCD sensors. The A490 really does work well with the 2007. I have one with the filter installed internally.
      FYI, your sample filters are going in the mail box today 🙂
      I’m looking forward to seeing your results.

      • MegaFlare

        Good to know. I was actually under the impression that the IR filter build into the camera had to be removed first.

        Looking forward to that special delivery, I should have both cameras delivered by next Tuesday.

        • geobduffy

          You DO need to remove the IR filter. After it is removed you can choose to put the blue filter in its place internally or mount on the outside of the lens. Outside is obviously better if you will be testing multiple filters.
          Sorry if I confused you.

          • MegaFlare

            Right, that makes sense now. That’s how you switch between the filters so quickly. Brilliant!

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