Huygens!

[Guest]

"while many of Earth's familiar geophysical processes occur on Titan, the chemistry involved is quite different. Instead of liquid water, Titan has liquid methane. Instead of silicate rocks, Titan has frozen water ice. Instead of dirt, Titan has hydrocarbon particles settling out of the atmosphere, and instead of lava, Titanian volcanoes spew very cold ice.

Titan is an extraordinary world having Earth-like geophysical processes operating on exotic materials in very alien conditions."

http://www.esa.int/SPECIALS/Cassini-Huy ... Y3E_0.html

[andersa]

You'd think... But they use their own proprietary formats and compression schemes, which are hideously clunky but do the job they want them to do. I think it might be so that they can put their own image headers and labels on the top of the files, which you can't do with PNGs or GIFs.

The astronomy and space research communities have some 40 years of experience capturing images and other data in space for transmission to Earth. When the Voyager images from Saturn were sent around 1980, state of the art graphics for off-the-shelf personal computers provided, say, eight colours and pretty low resolution (and many users were satisfied with b/w). The science community required a lot better, and thus had to develop their own formats and software. GIF came in the 1980's, but was hardly sufficient for science imaging. Maybe PNG would do well today, but I don't see much benefit in a general switch, scrapping years of software development for them.

I remember reading that the Voyager spacecrafts received new data compression software over the radio long after launch, to overcome some of the physical limitations incurred by broken transmitters, stuck antennas or whatever damages they had appearantly suffered in the asteroid belt. For 1970's technology, I consider that pretty amazing.

I don't know too much about the format that the cameras actually save the images as, I deal more with turning those into processed images.

Browsing the Cassini raw (?) image archive, I can hardly find any images with similar compression artefacts as those from Huygens. Maybe Cassini can afford to do less compression, thanks to higher bandwidth in the Earth communication link?

[Sky Pilot]

The science community required a lot better, and thus had to develop their own formats and software. GIF came in the 1980's, but was hardly sufficient for science imaging. Maybe PNG would do well today...

Would you mind explaining PNG? Is that a format somewhat like JPG?

[andersa]

Would you mind explaining PNG? Is that a format somewhat like JPG?

I'd say it's quite different from JPEG, though it combines a number of features from earlier image formats. Development of the PNG format was partly spurred by the Unisys patent controversy surrounding GIF, but I'm not very familiar with the technical details. For a collection of links about PNG, I recommend the Open Directory:
http://dmoz.org/Computers/Data_Formats/Graphics/2D/PNG/

[Evil Dr Ganymede]

Would you mind explaining PNG? Is that a format somewhat like JPG?

GIF was made for 8-bit images - with a pixel range going from 0 to 255. That makes it good for greyscale images, but lousy for true colour because obviously there are more than 256 colours. But if the image has less than 256 colours or greylevels, you're not changing the data if you save it as a GIF.

JPG can handle true colour, but it uses a compression algorithm that loses some of the data (I think that it works as I described earlier - areas that are close to the same colour get 'rounded down' so they are all the same colour). This means you can get compression blocks, and thus it's 'lossy compression' because you lose data.

PNG on the other hand can can handle true colour images, but uses a compression algorithm that DOESN'T lose any data (a 'lossless' compression). I don't know how it manages this, but it makes it a much better choice for full colour images.

[t00fri]

Not to forget: Unlike JPG, PNG can administrate an alpha channel besides the usual R G B color channels! That means you can do images with transparency or specular effects.

The compression rate of PNG can be adjusted and can be very high, despite its lossless nature. I am a great fan of PNG.

Bye Fridger

[Michael Kilderry]

The only problem with .png is that it is a lot bigger in file size than .jpg, that's why I use .jpg instead fro my addons most of the time.

Michael Kilderry

[t00fri]

After the methane rain...florishing Titan! Can you see the meadows, rivers and...daffodils?

Bye Fridger

[Michael Kilderry]

If only...

PS: You've accidentally put an e on the end of the name Titan, don't worry, simple mistake.

Michael Kilderry