Jim Bell Q'n'a, Questions Please Options

[djellison]

Jim Bell's agreed to do a brief Q'n'A in a few days time, so similar to the one I did for Steve, I want your questions! Try and keep it quite 'current' if you can, as we're going to make this more a 'news' outlet than a look back type chat.

We're going to try, if this one works, to do these every couple of weeks or so, a bit of Rover news and a bit of Q'n'A each time, but we'll see how this one goes first!

Fire away people

If they're all crap, don't worry, I've got LOADS in mind.


Doug

[algorimancer]

Here's a two part question for Jim Bell:

A) Why didn't the MER cameras use the Jpeg2000 file format specification (which is based on wavelet compression and an order of magnitude more efficient than standard jpegs) rather than using an in-house wavelet compression algorithm? Currently Nasa software must be used to view the raw image data, whereas with Jpeg2000 compression the raw images would have been immediately accessible with standard image editing/viewing software.

B) Would it be possible to post higher quality images to the exploratorium & jpl sites in Jpeg2000 format (same size, better quality) in addition to or instead of the currently used jpeg format?

Not only would use of Jpeg2000 for images in exploratorium provide better quality images, but it would also be a spur towards broader adoption of the format in browsers and other image software.

[djellison]

Currently Nasa software must be used to view the raw image data, whereas with Jpeg2000 compression the raw images would have been immediately accessible with standard image editing/viewing software.

Are you talking about the PDS IMG's - as the rules and regs for what you publish to the PDS are basically set in stone as I understand it.

I agree, better quality raw JPG's would be nice, but to be honest, so old and to date, fairly reliable is the system that's putting out the JPG's we see know, I'd not want to see it played with.

iirc, you'll get some Jpeg2000 goodness with HiRISE images though

Doug

[algorimancer]

Are you talking about the PDS IMG's - as the rules and regs for what you publish to the PDS are basically set in stone as I understand it.

I agree, better quality raw JPG's would be nice, but to be honest, so old and to date, fairly reliable is the system that's putting out the JPG's we see know, I'd not want to see it played with.

iirc, you'll get some Jpeg2000 goodness with HiRISE images though

Doug

Fundamentally I was referring to the images comming out of the the MER. As I understand it the compression used prior to transmitting the files is a type of wavelet compression (which is good), however why they opted to "wing it" versus using an ISO standard is what I'm wondering about. My guess is that the standard wasn't finalized at the time they were building the hardware, but it's just a guess. As to the PDS rules... it has been a few years since I last looked at the requirements, but since HiRISE is apparently using Jpeg2000, I would guess that MER could as well. I wonder whether the compression scheme in MER overlaps with that in Jpeg2000 so that a direct conversion would be possible without any loss of quality.

Thanks for mentioning HiRISE, I hadn't looked closely at that mission but after having a look at the home page it looks pretty exciting, particularly from the perspective of the sort of people who hang-out at this site

[ugordan]

As I understand it the compression used prior to transmitting the files is a type of wavelet compression (which is good), however why they opted to "wing it" versus using an ISO standard is what I'm wondering about. My guess is that the standard wasn't finalized at the time they were building the hardware, but it's just a guess.

The main reason for developing a proprietary compression algorithm was better performace in regards to data transmission packet sizes and error resilience, both specific to the medium the data are transmitted along - radio waves over the DSN network. It was heavily influenced by Jpeg2000, only adapted to a very specific use. I have a PDF describing the MER algorithm somewhere, but can't seem to dig it up now.

I wonder whether the compression scheme in MER overlaps with that in Jpeg2000 so that a direct conversion would be possible without any loss of quality.

While both standards are very similar in terms of compression principles, I don't believe they're that compatible. There are specifics to each algorithm that probably make a lossless conversion impossible.

[algorimancer]

I have a PDF describing the MER algorithm somewhere, but can't seem to dig it up now.
While both standards are very similar in terms of compression principles, I don't believe they're that compatible. There are specifics to each algorithm that probably make a lossless conversion impossible.

This may well be that PDF, which describes the ICER compression scheme used by MER and compares it with j2k and others:

http://tmo.jpl.nasa.gov/progress_report/42-155/155J.pdf

As I read it, it rather sounds like it is using something like a subset of capabilities of j2k. While it is clear that a non-lossless j2k image could be losslessly converted to the ICER format, the reverse is not obvious.

[ugordan]

This may well be that PDF, which describes the ICER compression scheme used by MER and compares it with j2k and others:

http://tmo.jpl.nasa.gov/progress_report/42-155/155J.pdf

Yes, that's exactly the one. Thanks for digging it up!

As I read it, it rather sounds like it is using something like a subset of capabilities of j2k. While it is clear that a non-lossless j2k image could be losslessly converted to the ICER format, the reverse is not obvious.

If the reverse is not possible, then the whole thing is useless in terms of releasing the PDS raw data as any recompression will make it less raw, and obviously not any different than regular JPEG. That's not to say it's impossible to repackage the bits and re-encode into J2000, as long as the wavelet coefficients aren't touched themselves.