[X] My Assistant

[Guest_AlexBlackwell_*]

The T35 flyby mission description is now online.

[ngunn]

And very exciting science promised - high res of Huygens landing area (at last) and regional 3D from ISS for example. Also VIMS over the northern 'lake district'. Iapetus will not steal the whole show over the next few weeks.

[ugordan]

Raws are in... and are near useless to any enthusiasts out there. At least the images showing the surface itself and not haze observations.
I wonder if the new raw page behavior is a bug or a "feature"?

[Bjorn Jonsson]

This beaviour started IIRC about 3 months ago and could easily be a "feature". It would be interesting to see what happened if someone complained.

In some cases this is perfectly OK (or (rarely) better than a contrast stretch) but in other cases not. For example the Iapetus Saturnshine shots will probably be completely ruined unless this gets fixed.

[ugordan]

Yes, I actually prefer this algorithm in almost all cases, except low phase, low contrast targets such as this. This appears to be a partial stretch, only the maximum brightness is scaled, not the minimum. It would be better if they then set the maximum scaling to something more bright than this neutral gray. I think this behavior started around T33 and coincided with the loss of some raws due to other reasons.

[ugordan]

This I call Into The Haze, a dodgy enhancement and animation of 24 wide angle frames (ranging from 39.6 to 24.7 thousand km, about 45 minutes timespan) that show northern haze layers on approach. Camera tracking gives an impression Cassini's headed straight into the haze. Shown at 2/3 original size:

There's a hint of the north pole collar disappearing to the left of the frame at the start of the sequence. The time interval is almost continuous - 4 pointing targettings with 6 frames each, obviously the slews took up some time so there are slight discontinuities there.

[scalbers]

Nice haze layer animation. Regarding the raw images page I sent an email via the "Contact Us" link with my $.02 worth of suggestions...

[nprev]

This I call Into The Haze

...words fail me. Uh...wow!

[ngunn]

Ugordan I like your movie! You seem to know why the latest surface raws have less contrast than on past flybys. Can you explain to us non image-tech people? I was looking forward to hunting for the Huygens landing site but the fog is giving me a headache.

[ugordan]

Ngunn, the Titan surface raws (as well as low phase icy moon views that don't show black space in the frame) don't have less contrast per se, this is more or less the amount of contrast the camera actually sees. What was the case with previous raws, before being submitted on the net as jpegs, is they were histogram stretched - the lowest brightness was more or less made black and the highest brightness white, thus increasing contrast.
What appears to be the case now is that the lowest brightness is left untouched and the highest brightness is set not to white, but to neutral gray (digital number value of 127 as opposed to 255 for white). They could have at least set it to white so jpegs would suffer fewer artifacts (the algorithm is dependant on contrast)

[ngunn]

Thanks. Everything is clear to me now - except Titan's surface features! I presume you and the other experts here can do the histogram stretch business as a matter of routine. Can anyone find that hi-res of Curien Station and make it intelligible?

[ugordan]

I presume you and the other experts here can do the histogram stretch business as a matter of routine.

Unfortunately, this is the point where JPEG makes things messy. It's a perceptual algorithm and it works by discarding less important (to the eye) detail, and low contrast areas fall into that category. A high contrast image will have better preserved spatial features (less blocky artifacts) than a low contrast one, for a preset quality encoder - which the raw page obviously uses. If the raw page was filesize controlled instead of "quality" controlled, it would probably be easier to pull out detail out of low contrast images. As it is, low contrast jpegs right now are very small files (sometimes around only 20 kilobytes) and that's beacuse detail was totally destroyed.

The other, lesser issue with non-histogram-stretched JPEGs is the lower dynamic range when you encode 12bit data into 8bit grayscales.

[mchan]

This I call Into The Haze,

Liked that animation. Sort of reminds me of "the energy barrier at the edge of the galaxy" in the original series Star Trek.

[Juramike]

Nice animation!

-Mike

[ugordan]

Thanks, everyone. I thought about making another animation rescaled to the same pixel scale, something similar to this, but the relatively short time interval, high noise and jpeg artifacts made it unlikely any change (apart from slight parallax) would be apparent. Once this stuff hits PDS it might be more worthwhile to try this again.