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Why are digital images taken by Mars explorers so low quality and why don't they use a camcorder??
Also why were images from the moon (1st landing) so low quality?
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#2
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Why are digital images taken by Mars explorers so low quality and why don't they use a camcorder??
Perdit:
Also why were images from the moon (1st landing) so low quality? Talk about your nattering nabob of negativism! The television images of the first humans to walk on the moon were the best live TV I had ever seen from the moon -- or from anywhere else, for that matter. As for the current photos from Mars, they have been excellent, too. If you'll be patient, and if all goes well, they'll get better. You want they should have sent an Eisenstadt? Davoud -- usenet *at* davidillig dawt com |
#4
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Why are digital images taken by Mars explorers so low quality and why don't they use a camcorder??
Good Questions.
First .. they didn't have Richard Crisp taking them!! ;-) Actually, the technology of the time during the late 60's/early 70's was just not all that well developed, to make the lunar videos sent from the moon to earth, as good as we can do these days. Just plain a result of the technology of the time. I would add that the still images and film brought back to earth is as good as any of today (IMO). The situation with Sprit is a bit more complex. The initial data being sent back is coming from a low gain antenna that is capable of about 1kb/sec. It has to share this slow data stream with a lot of other non image data this is crowding the initial flow from the rover. The high gain antenna is up and running (as of last night) and as the mission develops further, and until more defined objectives (that remain fluid until checkout, systems calibration, and ultimately spectroscopy) are accomplished, the picture quality will be on a ramp from low res, black & white, to what I believe will be the truly awe inspiring color images to come. A lot of data needs to be funneled through the antenna., and even the high gain is only on par with a 12K modem. That, and (of course) ... they need Mr. Crisp!! Awesome stuff you do Richard. Gary "Perdit" wrote in message m... Also why were images from the moon (1st landing) so low quality? |
#5
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Why are digital images taken by Mars explorers so low quality and why don't they use a camcorder??
Ok, thanks. And it looks like an well-informed answer to me.
However I do not quite understand the relation between 'modem' speed and image quality. 1k/s would be enough to produce a good quality image in little time, above all if you use jpg compression. The non-martian landscape in front of my house which I snap with my 2mp kodak looks wonderful at 150-200k (a 3 minute download at 1k/s). Also why can we see the 'stitches' in the panoramic picture composites?? I think there's still something we are missing here. I wish somebody from Nasa was so kind to give me a minute of his time and honor us with a response. |
#6
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Why are digital images taken by Mars explorers so low quality and why don't they use a camcorder??
In message , Perdit
writes Ok, thanks. And it looks like an well-informed answer to me. However I do not quite understand the relation between 'modem' speed and image quality. 1k/s would be enough to produce a good quality image in little time, above all if you use jpg compression. The non-martian landscape in front of my house which I snap with my 2mp kodak looks wonderful at 150-200k (a 3 minute download at 1k/s). I think you will find modem speeds are specified in bits per second so you are being roughly an order of magnitude optimistic about transfer times. It would take it around half an hour to send your image back. Also why can we see the 'stitches' in the panoramic picture composites?? Almost certainly it is policy to use the images without any cosmetic molestation. Quicker to do and makes it obvious where the frame edges are. Scientific images are not necessarily pretty provided they are fit for purpose. Regards, -- Martin Brown |
#7
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Why are digital images taken by Mars explorers so low quality and why don't they use a camcorder??
On 6 Jan 2004 04:03:53 -0800, (Perdit) wrote:
Also why can we see the 'stitches' in the panoramic picture composites?? Because nobody has taken the time to construct a high quality mosaic off these original images. I'm sure it isn't a high priority at this point. I'm still curious in what way you find the images poor. They look excellent to me- good resolution, low noise, what more do you want? Obviously, many were made under low light conditions. I have been bringing some of the raw images into Photoshop and adjusting the curves for better brightness and contrast, but that's just basic processing. Other than the small size, which I attribute to limited bandwidth, the images are great. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#8
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Why are digital images taken by Mars explorers so low quality and why don't they use a camcorder??
"Perdit" wrote in message om... Ok, thanks. And it looks like an well-informed answer to me. However I do not quite understand the relation between 'modem' speed and image quality. 1k/s would be enough to produce a good quality image in little time, above all if you use jpg compression. The non-martian landscape in front of my house which I snap with my 2mp kodak looks wonderful at 150-200k (a 3 minute download at 1k/s). Part of the 'key' to how modems achieve the rates they do, is that the link is bidirectional, and if data is lost, the receiver can ask for a retransmission. This is not possible with a space probe (think of the light speed delays involved), so normally data is encoded to allow sections to be lost, and yet the final results to be reliably retrieved. The 'downside' of this, is that this has the opposite effect to compression, making the amount of data that has to be sent increase. Speaking scientifically, any 'lossy' compression like jpeg, would not be acceptable either. The data rate also has to be shared with other sensors on the craft. The craft data rate, is typically around 8000bits/second, which with encoding to protect against data loss, a typical picture from a good quality scientific imager (say 5M pixels, at 16bits/pixel, shot through three seperate colour filters, and then using a hamming code), would take 5625 seconds to send!. Even a single video frame (say 307000 pixels, each using 8bits/pixel), would take 307 seconds to send. This can be bettered (very significantly), using lossless compression, but pictures will still take a _long_ time. The fastest link 'back', is by sending to the orbiter, then from this to Earth, which can receive about 7.5Mbytes of data in 8 minutes, but only once per Mars day. Direct transmissions to Earth, are also limited to a maximum of about three hours per day, by power (and heat) limitations. The link back, is also 'shared' by the various craft, further restricting the amount that each craft can send. The panoramic camera, can generate an image, that is 4000*24000 pixels. To shoot colour, would require three such images, giving one 'image', needing 576MB of data. Even if carefully compressed, then sent, this would occupy the entire transmission time for a couple of days!. Also why can we see the 'stitches' in the panoramic picture composites?? Because it takes a human time, to tidy up such joints. I think there's still something we are missing here. I wish somebody from Nasa was so kind to give me a minute of his time and honor us with a response. You are missing, two things. The first is just how restricted the 'link' is, and the second is that pictures that look pretty, will often have lost a lot of the scientific data they may contain. The pictures being sent, are targetted towards making accurate colour measurements, not images that necessarily look pretty. Hence the massive compressions typically used on consumer cameras, are not suitable for spacecraft data. The pretty pictures will appear, as processors on the ground re-assemble the data, and cover the joints... Best Wishes |
#9
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Why are digital images taken by Mars explorers so low quality and why don't they use a camcorder??
Thanks Roger.
This is a much better answer than I managed to provide. Gary "Roger Hamlett" wrote in message ... "Perdit" wrote in message om... Ok, thanks. And it looks like an well-informed answer to me. However I do not quite understand the relation between 'modem' speed and image quality. 1k/s would be enough to produce a good quality image in little time, above all if you use jpg compression. The non-martian landscape in front of my house which I snap with my 2mp kodak looks wonderful at 150-200k (a 3 minute download at 1k/s). Part of the 'key' to how modems achieve the rates they do, is that the link is bidirectional, and if data is lost, the receiver can ask for a retransmission. This is not possible with a space probe (think of the light speed delays involved), so normally data is encoded to allow sections to be lost, and yet the final results to be reliably retrieved. The 'downside' of this, is that this has the opposite effect to compression, making the amount of data that has to be sent increase. Speaking scientifically, any 'lossy' compression like jpeg, would not be acceptable either. The data rate also has to be shared with other sensors on the craft. The craft data rate, is typically around 8000bits/second, which with encoding to protect against data loss, a typical picture from a good quality scientific imager (say 5M pixels, at 16bits/pixel, shot through three seperate colour filters, and then using a hamming code), would take 5625 seconds to send!. Even a single video frame (say 307000 pixels, each using 8bits/pixel), would take 307 seconds to send. This can be bettered (very significantly), using lossless compression, but pictures will still take a _long_ time. The fastest link 'back', is by sending to the orbiter, then from this to Earth, which can receive about 7.5Mbytes of data in 8 minutes, but only once per Mars day. Direct transmissions to Earth, are also limited to a maximum of about three hours per day, by power (and heat) limitations. The link back, is also 'shared' by the various craft, further restricting the amount that each craft can send. The panoramic camera, can generate an image, that is 4000*24000 pixels. To shoot colour, would require three such images, giving one 'image', needing 576MB of data. Even if carefully compressed, then sent, this would occupy the entire transmission time for a couple of days!. Also why can we see the 'stitches' in the panoramic picture composites?? Because it takes a human time, to tidy up such joints. I think there's still something we are missing here. I wish somebody from Nasa was so kind to give me a minute of his time and honor us with a response. You are missing, two things. The first is just how restricted the 'link' is, and the second is that pictures that look pretty, will often have lost a lot of the scientific data they may contain. The pictures being sent, are targetted towards making accurate colour measurements, not images that necessarily look pretty. Hence the massive compressions typically used on consumer cameras, are not suitable for spacecraft data. The pretty pictures will appear, as processors on the ground re-assemble the data, and cover the joints... Best Wishes |
#10
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Why are digital images taken by Mars explorers so low quality and why don't they use a camcorder??
OK, Thanks I now better understand the limitations but you can agree
with me that it should be a priority to get some crystal-clear images, now or after procecessing or whenever. Even the latest 12Mp image that is being hyped is good, right, but it does not look like 12MB clarity. This is the CCD imagin forum. I am sure many of you have a decent 3-5 Mp digital camera. Take a picture of any surface landscapè. The clarity from this 3-5 cameras is amazing. I am impressed by the 12Mp Mars image, but not because of the clarity but because it is Mars and it had never seen like that before. Looking at other images in the same set what i can see is lightly out of focus stones. That's pretty obvious and any photo enthusiast can see that. |
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