5 ms·

They use the same kind of compression as the last mission. JP2, I believe. https://en.wikipedia.org/wiki/JPEG_2000 https://en.wikipedia.org/wiki/JPEG_2000 I'm

They use the same kind of compression as the last mission. JP2, I believe. https://en.wikipedia.org/wiki/JPEG_2000 https://en.wikipedia.org/wiki/JPEG_2000 I'm not sure that data compression has progressed that much since Curiosity in 2012 or Insight in 2018. There have been some formats that have improved compression at the expense of large amounts of memory or processing power, but neither of those are abundant on a rad-hardened processor. Neither is electricity. Neither are the toolchains to process such images very widespread or as well understood.

hanniabu 6y ago
Any idea how much storage it has? I would think it'd have to be TBs to store all these images, logs, and other data for years while making sure they have enough memory so that they're not limited and if the rover stays there for longer than intended.
- Hnrobert42 6y ago
  Why would it need to continue to store things after successful receipt on Earth?
  - leephillips 6y ago
    Very off-site backup.
- azernik 6y ago
  Once it's been sent to Earth, they drop it. Curiosity's main computer had a flash drive of 2GB, and each of the big cameras had an 8GB flash drive on board. I doubt Perseverance is much changed from that; the main computer is IIRC a spare part from the Curiosity production. Rad-hardened computer hardware is expensive and bulky. You don't add storage or processing power that you don't absolutely need. See https://www.ontrack.com/en-us/blog/how-to-store-data-on-mars https://www.ontrack.com/en-us/blog/how-to-store-data-on-mars and https://mars.nasa.gov/mars2020/spacecraft/rover/brains/ https://mars.nasa.gov/mars2020/spacecraft/rover/brains/
walrus01 6y ago
One of the obvious constraints is that for science reasons they transmit each image in a lossless format, so we're up against the limits of what a lossless image compressor can do. If there were a future mission's requirement to send back lossy images first, and CPU power was significant, something like AVIF or JPEG-XL would likely be a candidate. https://netflixtechblog.com/avif-for-next-generation-image-coding-b1d75675fe4?gi=87b2c9da8c1c https://netflixtechblog.com/avif-for-next-generation-image-c... ICER appears to be what they're using now for lossless: https://en.wikipedia.org/wiki/ICER https://en.wikipedia.org/wiki/ICER
- Robotbeat 6y ago
  Thanks for that. Yes, they do both lossless and lossy compression. I think sometimes they may send the lossy image (especially if for a navigation or engineering camera) and request a lossless image if there's something particularly interesting.
- topkeks 6y ago
  AVIF has a lossless mode, which is quite a lot better than PNG for example.
- mleonhard 6y ago
  According to the graph on p.42, the 20 MHz CPU compresses at a rate of about 20us/pixel. So the 1024x1024 images take about 20 seconds each to compress. There are 2,000 "normal" sized images on the website [0]. If each of these was 1024x1024, they took 11 hours to compress. So Perseverance spends about 7% of its CPU time on image compression. [0] https://mars.nasa.gov/mars2020/multimedia/raw-images/ https://mars.nasa.gov/mars2020/multimedia/raw-images/
- Robotbeat 6y ago
  Found some more info. They're using ICER for lossless, like you say. They're also using LOCO for lossless compression. For lossy compression, the JPEG encoding was inherited from the Mars Insight lander (in 2018). Page 36 from the PDF: https://link.springer.com/article/10.1007/s11214-020-00765-9 https://link.springer.com/article/10.1007/s11214-020-00765-9
ptstomp 6y ago
I can't find references to JPEG 2000 on this report: https://link.springer.com/article/10.1007/s11214-020-00765-9 https://link.springer.com/article/10.1007/s11214-020-00765-9 Are they being re-encoded into regular JPG files when being shown online?
- Robotbeat 6y ago
  Look for “JP2”. It is used for other spacecraft that are part of the Mars fleet.
- Robotbeat 6y ago
  You're right. They're encoding just regular JPEG for lossy compression. They're also using either ICER and LOCO for lossless compression. JP2 has been used for other Mars spacecraft (the HiRise orbiter, I believe), but the JPEG encoding was inherited from the Mars Insight lander (in 2018).

hanniabu 6y ago

Any idea how much storage it has? I would think it'd have to be TBs to store all these images, logs, and other data for years while making sure they have enough memory so that they're not limited and if the rover stays there for longer than intended.

Hnrobert42 6y ago
Why would it need to continue to store things after successful receipt on Earth?
- leephillips 6y ago
  Very off-site backup.
azernik 6y ago
Once it's been sent to Earth, they drop it. Curiosity's main computer had a flash drive of 2GB, and each of the big cameras had an 8GB flash drive on board. I doubt Perseverance is much changed from that; the main computer is IIRC a spare part from the Curiosity production. Rad-hardened computer hardware is expensive and bulky. You don't add storage or processing power that you don't absolutely need. See https://www.ontrack.com/en-us/blog/how-to-store-data-on-mars https://www.ontrack.com/en-us/blog/how-to-store-data-on-mars and https://mars.nasa.gov/mars2020/spacecraft/rover/brains/ https://mars.nasa.gov/mars2020/spacecraft/rover/brains/

walrus01 6y ago

One of the obvious constraints is that for science reasons they transmit each image in a lossless format, so we're up against the limits of what a lossless image compressor can do. If there were a future mission's requirement to send back lossy images first, and CPU power was significant, something like AVIF or JPEG-XL would likely be a candidate. https://netflixtechblog.com/avif-for-next-generation-image-coding-b1d75675fe4?gi=87b2c9da8c1c https://netflixtechblog.com/avif-for-next-generation-image-c... ICER appears to be what they're using now for lossless: https://en.wikipedia.org/wiki/ICER https://en.wikipedia.org/wiki/ICER

Robotbeat 6y ago
Thanks for that. Yes, they do both lossless and lossy compression. I think sometimes they may send the lossy image (especially if for a navigation or engineering camera) and request a lossless image if there's something particularly interesting.
topkeks 6y ago
AVIF has a lossless mode, which is quite a lot better than PNG for example.
mleonhard 6y ago
According to the graph on p.42, the 20 MHz CPU compresses at a rate of about 20us/pixel. So the 1024x1024 images take about 20 seconds each to compress. There are 2,000 "normal" sized images on the website [0]. If each of these was 1024x1024, they took 11 hours to compress. So Perseverance spends about 7% of its CPU time on image compression. [0] https://mars.nasa.gov/mars2020/multimedia/raw-images/ https://mars.nasa.gov/mars2020/multimedia/raw-images/
Robotbeat 6y ago
Found some more info. They're using ICER for lossless, like you say. They're also using LOCO for lossless compression. For lossy compression, the JPEG encoding was inherited from the Mars Insight lander (in 2018). Page 36 from the PDF: https://link.springer.com/article/10.1007/s11214-020-00765-9 https://link.springer.com/article/10.1007/s11214-020-00765-9

ptstomp 6y ago

I can't find references to JPEG 2000 on this report: https://link.springer.com/article/10.1007/s11214-020-00765-9 https://link.springer.com/article/10.1007/s11214-020-00765-9 Are they being re-encoded into regular JPG files when being shown online?

Robotbeat 6y ago
Look for “JP2”. It is used for other spacecraft that are part of the Mars fleet.
Robotbeat 6y ago
You're right. They're encoding just regular JPEG for lossy compression. They're also using either ICER and LOCO for lossless compression. JP2 has been used for other Mars spacecraft (the HiRise orbiter, I believe), but the JPEG encoding was inherited from the Mars Insight lander (in 2018).