Exposing PseudoAstronomy

August 16, 2012

Podcast Episode 48: Image Processing and Anomalies, Part 2


Alrighty, episode 48 has been posted, and the companion video has been expectedly delayed.

This episode is almost as long as part 1, and I still left stuff out. Sharpening and filters and stuff like that is going to wait for a later episode. The topics discussed this time are: Dynamic range, noise, rotation and resizing, and levels, curves, and contrast.

The bottom-line with this episode is that even the most seemingly innocuous adjustments – like Auto Levels, or rotate by 10°, or increase the size by 50% – are going to change the information that was originally there, and often it will do it destructively such that you cannot make the reverse change and get the original back.

There was a bit of feedback this time and a discussion of some write-ins for the puzzler last time.

2 Comments »

  1. Love the show etc., etc.. (No really, just want to keep it short.)

    You mention the need for white balance in the Mars pictures to make them look as a human would see the landscape. Skipping the tricky part of human perception and our wonderful ability to auto-calibrate what “white” is, you mentioned that the martian dust colors the air red with a “haze”:

    Episode 48: “It’s like it’s constantly shooting photos through a haze, so the photos are going to have a red cast to them.”

    I wonder if it isn’t more due to the high altitude dust in the atmosphere diffracting away shorter wavelengths just like a forrest fire might do on earth, letting more of longer—redder—wavelengths from the sun through, thus giving a red cast to the light, regardless if there is dust in the air between the camera and the object being photographed.

    I’m actually a bit curious how they calibrate the camera since a known white surface on the vehicle would invariably pick up colored dust. I can think of three or four ways of solving it, but I don’t know what approach they are actually using. Doesn’t it get tricky to

    More things I don’t know, but would love to hear about are (1) how the spectrum is calibrated. Here on earth we use the black body temperature to talk about color temperature for film: 6500K for “a sunny day with clouds in Washington DC” [according to Kodak] or 3200K for incandescent light. All gross simplifications as human color perception is vastly more complicated than can be captured with a single number. Still, it gets you in the ballpark.

    I would love to be able to step into a museum exhibit that as closely as possible mimicked the light of Mars—intensity and color—and be able to see both simulated martian stuff as well as familiar earth objects.

    (2) How clear is the Martian atmosphere on a “clear day”?

    (3) How much dust is there at ground level and how fine is it? Is the atmospheric dust like a bit like a sandstorm, or more like forrest fire smoke? Again, I would love to be able to enter a simulation where I could get a “feel” for it. I am also curious how it smells—but we might not find that out in my lifetime [sigh]. Are there environments on earth with similar dust such high altitude deserts?

    I remember hearing the lunar astronauts talking about how the lunar dust smelled when they entered the LEM after a days work. Apparently it smelled like gunpowder:

    —-
    From Apolo 15 Post-EVA-1 Activities http://www.hq.nasa.gov/alsj/a15/a15.eva1post.html

    126:16:16 Irwin: There’s a funny smell in here.
    126:16:17 Scott: Yeah, I think that’s a lunar dirt smell. (Pause) Never smelled lunar dirt before, but we got most of it right here with us.

    [Jones – “How would you describe the smell of lunar dirt?”]
    [Scott – “Like gunpowder.”]

    [Jones – “That’s what most people say.”]

    [Scott – “I hadn’t heard that before we went. I don’t think.”]

    [Jones – “Here, you don’t actually describe it as gunpowder.”]

    [Scott, from a 1996 letter – “I actually whispered it to Jim so that nobody would become alarmed.”]
    —-

    (4) If I understand it right, there is more fine dust in the martian atmosphere than typical here on earth. Is that right, and if so is it mostly due to the very dry atmosphere, or thin low density and high speed winds responsible too?

    (5) Do we know what the distribution of particle sizes is? How does it vary with altitude. (Question 5 is sort of a more objective version of 3’s “how does it feel”.)

    –j

    PS I don’t know how you manage to keep a cool head amidst the ziggurat bull crap. Amazing… and _greatly_ appreciated!

    Comment by Johan™ Strandberg — August 24, 2012 @ 5:01 pm | Reply

    • I’ve finally found a good episode to put this in for Q&A. Slated for the “True Color of Mars” episode, tentatively slated for March 8.

      Comment by Stuart Robbins — January 8, 2013 @ 6:52 pm | Reply


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