Is The Mars Rover Cam Life-Blind?

This may apply if the filters covered the entire spectrum and you were using CMYK to create the images, but they are created with RGB. It is the ABSENCE of light in the range of the transmittance of the filter that shows color, not the other way around.

I stand by my conclusions.

And if I am wrong what colors can the cam not see?

I would not have posted this if I had not already confirmed it with an expert on chlorophyll.

[Edited on 11-2-2004 by ArchAngel]

Originally posted by ArchAngel
This may apply if the filters covered the entire spectrum and you were using CMYK to create the images, but they are created with RGB. It is the ABSENCE of light in the range of the transmittance of the filter that shows color, not the other way around.

This makes me think that your understanding of hyperspectral imaging is not really what it needs to be, in order to discuss this properly.

First off, you need to understand how narrow-bandpass frequency filters work in conjunction with CCD cameras. From a perspective where that understanding is in place, your statement makes no sense at all.

It can be easy to get confused if you come from an emulsion-film background and are used to the types of filters typically used with that technology (absorption filters).

These are not the same kind of filters, because CCD technology is radically different from film. These are BANDPASS filters, which are the logical opposite of putting a regular camera filter in front of a lens. These are also called interference filters and/or "dichroic" filters.

There's a really neat webpage that explains the difference between the filter types. Give it a view here.

Those who work with audio files are probably familiar with the difference between a bandpass and a band-reject filter, but many photographers may not be. There are different terms to describe the behavior of a filter that BLOCKS a narrow range of frequencies... notch filter, band-reject filter, bandstop filter, etc.

Pancam doesn't use the kind of filters that you seem to be thinking of. I can see where that could lead you to topsy-turvy conclusions, because you might intuitively think that the L5 filter BLOCKS that range of frequencies, and hence that darkness indicates the PRESENCE of light.

That's not how they work. The narrow bandpass (interference) filters block EVERYTHING BUT that particular narrow range of frequencies... so the presence of those frequencies gives a bright signal, not a dark one.

That's why there's no need for "negatives" when working with this technology... you don't have to take darkness and interpret it as brightness in those frequencies. That makes the data much easier to work with, IMO.

Kano provided some links to nice reference materials in his rather canonical thread on the subject.

When a shot is taken on one of the Pancam cameras (either the left or right) with a narrow bandpass filter in place (say, L3 through L7), what happens is that (basically) all frequencies of light that fall outside that particular narrow band are BLOCKED by the filter. The photons that make it through are photons that are within that narrow bandpass (typically plus-or-minus 10 nm or so).

Those photons hit the CCD array, and create electrons trapped in the CCD wells, and the act of reading them out gives a rough "count" of how many electrons were in each well for that particular shot. The more electrons, the stronger the signal.

That set of per-pixel signals is normalized to set the highest value at a reading of 255, and all of the other values are scaled accordingly. That array of pixels is then processed, compressed and transmitted, and what we see posted is typically a JPEG-compressed version of that data set.

What does that mean? Well, the image that we see from an L5 shot, for instance, shows us bright signals only from photons that came in within a frequency of roughly 520-540 nm. If there were very few photons in that range, the associated pixel will be dark.

If something is green in human vision when lit by sunlight, you can be well-assured that an L5 shot from the Pancam of that particular thing in sunlight would show it as bright.

For something with chlorophyll, it would be bright in L5 while simultaneously dark in L3 and L6. So when you use a computer to mix Pancam shots of a scene with L3 for red, L5 for green, and L6 for blue, you would see chlorophyll-rich plants as pretty vividly green on your computer screen.

And if I am wrong what colors can the cam not see?

I'll assume that when you say "colors", you mean colors that human eyes can register.

For something to be "color", but still show as consistently dark (i.e. not seen) on all Pancam shots with all lenses, the object in question would need to have a remarkably strange response curve. It would have to absorb all frequencies except for a narrow-enough band that all of the response curve would somehow fit between the filter ranges... but keep in mind that L1 is an unfiltered shot. You see the response curve for L1 in the background of one of the pictures you posted. Notice that the L1 position has non-zero response in the "gaps" that are not specifically covered by individual bandpass filters.

Something with that radical of a response curve would almost certainly create an unusual situation when they compared L1 data to the other filters... you could likely see it as somewhat bright in L1 but extremely dark in all of the other filters, which creates a "warning flag" immediately that there is something exceedingly strange in the shot.

From that perspective, I have trouble imagining anything that a human could see, that couldn't be detected at all by the Pancam.

I would not have posted this if I had not already confirmed it with an expert on chlorophyll.

Yes, but your quote indicates that you're dealing with someone who is familiar with old-school photography, but almost certainly doesn't understand hyperspectral imaging with narrow bandpass interference filters... which are the exact opposite of what typical photography buffs think of when you say "filter". Dichroic (interference) filters are top-end technology, and give counterintuitive results for those used to gel and glass filters.

Of course that leads to inaccurate conclusions, and your statements about the absence of light indicating color. That's an appropriate mindset for emulsion technology with gel/glass absorption filters, but not for hyperspectral imagery with narrow-bandpass filters. They work in exactly the OPPOSITE way. Light means light, instead of darkness meaning light.

Before "standing by your conclusions" any more, please open your mind to the possibility that you have become horribly confused by the term "filter" meaning the opposite of what you think it does (for this technology).

There's a really great technical PDF file offered by Cornell that gives excellent data to help understand how the Pancam really works. I'd recommend that it be read (and understood) by anyone who wants to talk intelligently about what the Pancam "can't do".

It's not your father's Polaroid... it's radically different technology from that, and understanding the results and capabilities requires understanding the difference.

[Edited on 2-11-2004 by BarryKearns]

Originally posted by McGotti
The mars rover is a fake..its been faked from the very top of the space galatic society..I have proof of this and will post it on another occasion once i feel safe enough that the mibs are not watching me...

will keep you posted

Oooga Booga.......

The narrow bandpass (interference) filters block EVERYTHING BUT that particular narrow range of frequencies... so the presence of those frequencies gives a bright signal, not a dark one.

I believe this supports my theory.

There are colors the cam cannot see.

Rather than cut-n-paste I refer this discussion.

www.godlikeproductions.com.../14/04&replies=137
No registration needed, and Anonymous posting.

[Edited on 14-2-2004 by ArchAngel]

Originally posted by ArchAngel
Rather than cut-n-paste I refer this discussion.

www.godlikeproductions.com...

The link says "thread is no longer available".

Sorry, Archangel, but Barry's explanation makes a lot more sense to me than your theory.

Besides, you are basing your entire theory on one premise that I feel is totaly eroneous.

You expect to see chlorophyl on Mars.

Mars is not Earth. It is wrong to attempt to apply terestrial biology to Mars. Besides, even on Earth there are a few life forms that are totally independant of chlorophyl for energy.

Sorry.

corrected link

Algae


green

Algae with red channel removed


Orange

NASA pics of Mars:


Orange

The best place to hide something is in plain sight.

Fine, Archangel, but again, you are asuming that the conditions for the evolution of blue green algae are the same for mars as they were on Earth. That is a major assumption that does not really have a much in the way of scientific suport.

That is not an unreasonable expectation within the same solar system. If looking at annother solar system or galaxy then I would want to believe a significant difference in lifeforms.

Arch, as Barry pointed out, for something to be invisible to the Rovers Pancam it would have to have an extremely unlikely reflectance spectra. Chlorophyll is easily noticeable with the filter range available.

Originally posted by THENEO
That is not an unreasonable expectation within the same solar system. If looking at annother solar system or galaxy then I would want to believe a significant difference in lifeforms.

Why?

Would you also expect to see algae on Venus, how about Jupiter?

The point is, although Mars is similer to the Earth in many ways, it is different enough that I think that it is unreasonable to expect that the same chemical processes that led to life on Earth would happen in the exact same way on Mars.

"Sensitive Dependance on Initial Conditions" and all of that



[Edited on 14-2-2004 by HowardRoark]

Originally posted by Kano
Arch, as Barry pointed out, for something to be invisible to the Rovers Pancam it would have to have an extremely unlikely reflectance spectra. Chlorophyll is easily noticeable with the filter range available.

Look at the transmittance gaps between the filters, and the absorption of chlorophyll.

[Edited on 14-2-2004 by ArchAngel]

Originally posted by HowardRoark

Originally posted by THENEO
That is not an unreasonable expectation within the same solar system. If looking at annother solar system or galaxy then I would want to believe a significant difference in lifeforms.

Why?

Would you also expect to see algae on Venus, how about Jupiter?

The point is, although Mars is similer to the Earth in many ways, it is different enough that I think that it is unreasonable to expect that the same chemical processes that led to life on Earth would happen in the exact same way on Mars.

"Sensitive Dependance on Initial Conditions" and all of that



[Edited on 14-2-2004 by HowardRoark]

Howard you made yourself look bad there. You and I and everyone else knows why Mars and Jupiter are different. Jupiter is a gas giant. Ahem...

True Howard, but we do have to start the search with what we are familiar with. Hence the search for evidence of water.

Obviously blue-green algae on the surface is somewhat of an exaggerated example. But any search would have to begin with what we would expect to find based on the only Biology we know, which is Earth-bound Biology.

Originally posted by THENEO


Howard you made yourself look bad there. You and I and everyone else knows why Mars and Jupiter are different. Jupiter is a gas giant. Ahem...

What about Venus, then.

don't be obtuse.

The point is, that we are talking about two entirely diferent planets. Mars is not the same as Earth.

What you see, and what you do not see are all part of what you see.

The monitor is a light source, not reflection.

If there were no light you could not see color.

L6 image of the sundial.



It would be used as the blue channel in an RGB image of either method. The chip on the lower right corner is blue as you see blue. It is very bright because it is blue, and there is little blue anywhere else other than bits on the rover. The ground is especially dark.

It is blue (as you see blue) because it reflects blue light.



Here it is composited RGB with only the blue channel.

It looks yellow because it�s blue light.

......

You need the other colors in the RGB to see the blue.



This is L4 which is used for the red channel. The blue chip is dark here because it does not reflect red light, and the ground is bright because it does.



Here it is with L4 only RGB composited as red.

It looks baby blue because the other parts of the color are not there.

Color is as much the presence, and absence of light.

Where blue-green algae is most different than the surroundings is where the big gap is.

[Edited on 14-2-2004 by ArchAngel]

Originally posted by ArchAngel
Look at the transmittance gaps between the filters, and the absorption of chlorophyll.

By this am I to infer you didn't bother reading Barry's post?

I'll give you a hint.

absorption of chlorophyll.

Not reflectance.

Again, AA, please explain why you think that algae would even be present on Mars?

Originally posted by Kano

Originally posted by ArchAngel
Look at the transmittance gaps between the filters, and the absorption of chlorophyll.

By this am I to infer you didn't bother reading Barry's post?

I'll give you a hint.

absorption of chlorophyll.

Not reflectance.

BOTH determine color.