RGB vs. Near-IR perspectives of Silicon Valley

4 responses to “RGB vs. Near-IR perspectives of Silicon Valley”

1. 

   jurvetson

   Nov 14, 2018 at 5:01 pm

   Burns are barren of chlorophyll… Here is an image of the Woolsey fire that scorched Malibu, shared recently by Planet on TwitterThe official fire perimeter is outlined with a thin white line, but, as you can see, there are some unburned areas within… perhaps of keen interest for evaluated homes in the region.

   "Do the Impossible" — a motivational message on the side of a Dove satellite…(my photo with a very shallow DOF, shooting f/0.95)

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2. 

   fisheggs

   Nov 15, 2018 at 7:14 pm

   Ack – as someone in the community who uses remote sensing a great deal – I can’t let this stand! The vegetation isn’t red-shifted – the image on the right is a false-color composite where they’ve simply set the "red" value for each pixel equal to the NIR brightness, (green and blue are usually set to the brightness as observed at red and green wavelengths, respectively).

   In class we show a well-known rgb image (moon landing with flag) as grayscale for each of the 3 wavelengths and let the students figure out which is which. We spend a lot of time discussing colormaps, since you often see things in the literature or advertising that is trying to "sell" a particular band combination as "better" than others – but the choice of colorscale can impact that pretty heavily.

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3. 

   P^2 – Paul

   Nov 15, 2018 at 9:49 pm

   Chlorophyll also is fluorescent: some of the blue light it absorbs is re-emitted in the NIR, making it brighter in the NIR than the underlying cell structure alone would be.

   Coincidentally, that NIR fluorescent output happens around where water starts to absorb very strongly, making the water look black.

   It’s also where atmospheric Rayleigh scattering (the one responsible for blue sky) is much lower, so background atmospheric haze is relatively low, further increasing the image contrast.

   The three effects (chlorophyll fluorescence, water absorption, and low atmospheric scattering) make excellent water-vegetation contrast.

   Picking red as the color to represent the NIR band does make it even more eye-catching.

   It’s too bad our eyeballs can only really see three colours in a small slice of the spectrum. There’s so much more to see.

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4. 

   jurvetson

   Nov 16, 2018 at 3:56 am

   Yes, I was marveling at the pentachromatic color space of some birds here. Thanks for the added detail.

   fisheggs – I clarified the caption text (hopeful better). It was meant to be a simple reference to the color-mapping, shifting from NIR to red. I did not mean redshifting in the doppler sense.

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