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Dawn Survey Orbit Phase, First orbital phase
NickF
post Aug 19 2011, 07:52 PM
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QUOTE (elakdawalla @ Aug 19 2011, 12:09 PM) *
That image was released 2 weeks ago -- why post it now? Was there something about it you wanted to discuss?


Indeed - I wasn't paying sufficient attention to the date when I posted it. Mea culpa.


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Stefan
post Aug 21 2011, 08:17 AM
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QUOTE (elakdawalla @ Aug 19 2011, 08:24 PM) *
Photojournal always has both TIFF and JPEG versions of an image. In rare, horrible cases, the TIFF has been made from a JPEG, but in most cases (including, as far as I can tell, Dawn), the TIFF is made from a file that was provided to the webmaster in some uncompressed format, and the lossily compressed JPEG made from that.

I know for a fact that for Dawn, Photojournal TIFF images have been converted from JPEG. At least some, possibly not all.

I am not so sure this only rarely happens.
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elakdawalla
post Aug 21 2011, 04:03 PM
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Well, shoot. That's stinky. But thank you very much for clearing that up. I guess the question then is where to get the least JPEGged images. I would assume that's still Photojournal.


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walfy
post Aug 21 2011, 07:10 PM
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QUOTE (Stefan @ Aug 21 2011, 12:17 AM) *
I know for a fact that for Dawn, Photojournal TIFF images have been converted from JPEG. At least some, possibly not all.

I am not so sure this only rarely happens.


I've always wondered about this as well. One would assume that the spacecraft beams the images to earth in JPEG format, with at least a little compression rendered on the original, considering the bandwidth limitations. TIFF images take up many more kilobytes than JPEG, so I would be very surprised if TIFF images are generated on the spacecraft for transmitting to Earth.
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ugordan
post Aug 21 2011, 07:15 PM
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QUOTE (walfy @ Aug 21 2011, 09:10 PM) *
One would assume that the spacecraft beams the images to earth in JPEG format

Spacecraft transmit neither JPEG nor TIFF format down to Earth. Actual telemetry format of the files will look nothing like computer formats we use here on the ground. Depending on the lossy compression scheme used on the spacecraft the algorithm can be pretty close to JPEG, though. However, not all data has to be returned losslessly compressed.

In short, the formats Photojournal uses have nothing to do with what spacecraft use.


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JohnVV
post Aug 21 2011, 07:18 PM
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It has been my personal belief ,for the last 10 years, that jpeg should be illegal

it was good in replacing the 8 bit indexed gif back in the 90's and was good for 24k dial-up
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ugordan
post Aug 21 2011, 07:36 PM
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I was hoping it would get replaced by jpeg2000 and dispose of those blocking artifacts, but alas it was not to be.

Anyway, we digress...


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volcanopele
post Aug 21 2011, 08:21 PM
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For the record, I always send along PNGs when I have any product that would go into the Planetary Photojournal.

PNG FTW!


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JohnVV
post Aug 21 2011, 08:23 PM
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we could remove them
for image "PIA14673.jpg" the tiff is good
before
[attachment=25346:jpg.art1.png]
after
[attachment=25347:jpg.art2.png]

gmic dose a good job, though some detail is lost .
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ugordan
post Aug 21 2011, 08:30 PM
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QUOTE (volcanopele @ Aug 21 2011, 10:21 PM) *
PNG FTW!

QFT.


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Juramike
post Aug 22 2011, 01:55 AM
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New image release today has some more false-color fun!

http://photojournal.jpl.nasa.gov/catalog/PIA14677


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Juramike
post Aug 22 2011, 04:03 AM
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Hokay, played with this. Red and blue are 750 to 450 and 450 to 750. So took those two channels and created a grayscale image of each then overlayed them at 50%. Whaddya know, they come out almost to a bland 128 pixel blandness. Put both of those in red and blue channels. Then put the green channel of PIA14677 back in.

Green channel is 750 to 950 nm ratio. Fe absorbs at 1000 um. So Hi Fe will have a "Hi" ratio (bright).

(Overaly HiPass filtered image for details, adjust green channel gamma and...)

Et voila, a map of Fe minerals: Iron-O-Vision:

Attached Image



Green is Fe enriched, magenta is Fe depleted.





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Juramike
post Aug 22 2011, 04:08 AM
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If I'm gonna guess, in this region there is a thin layer of Fe-enriched material. Mid-size recent craters dig this up and splat it on the surface as ejecta.

Bigger craters dig much deeper into an Fe-depleted layer and this lands on top of the other ejecta close to the crater. So the larger craters have an inner ejecta ring of Fe-depleted material (magenta) inside the Fe-enriched material. The uppermost poofy dust layer seems to be Fe-depleted. The landslides inside the crater also seem to be Fe-depleted (magenta).

Just my guess....


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Juramike
post Aug 22 2011, 04:15 AM
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Oooo, and notice how some of the craters in the lower part of the image have a touch of green at the center, but craters bigger than this don't. Those correspond to about 11 pixels, (x 450 m pixel) so, 5.3 km crater. Maybe indicating the Fe-rich layer is maybe only 4-5 km below the surface?


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Paolo
post Aug 22 2011, 05:37 PM
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wow! Up and Down in Vesta's Cratered Terrain


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