SCI/TECH: What Color Is Mars, Really?

That is all very interesting, and I think I basicly understand it, but what if there are blue or green objects on Mars?

What would they look like, or are we incapable of seeing them with the cam?

Where are the calibration images for these filters?

Why is the calibration image NASA published in normal light?

One thing: B&W movies could be re-recorded in colour. This *could* be done with this photo if it's turned into the greyscale.

This requires specialistic software, I think. With this, after bringing saturation to zero level, with use of this software, original colours from mars would be restored.
My mum used to work in the film industry but unfortunately has never done this stuff. And today she has no way to get to this.
The theory is that a specific density (or wavelength) on the b&w photo would have a colour assigned (manually, by someone or automatically by the program).

I don't know how it ACTUALLY works, tell me if this idea is impossible to realise.

[Edited on 12-1-2004 by Johnny]

NASA has a new panorama image photojournal.jpl.nasa.gov... But this time, they cropped out the color-calibration sundial.

edit: oops... never mind

[Edited on 12-1-2004 by Groo the Wanderer]

Originally posted by SkepticOverlord
NASA has a new panorama image
photojournal.jpl.nasa.gov...
But this time, they cropped out the color-calibration sundial.

Wonder what this means!
"A higher-resolution image will be made available once it has been processed"

Sounds like they need to sort it out, to make it fit with the other photos so far.

Yeah... I'm with our esteemed resident science-nut Kano on the explanations and basis behind all the color theory and filter information. It makes good sense, and all... but the big question in all of this is... why... why filter the colors? For what purpose? And if they are filtering the colors for a good reason... why not explain it?

"why filter the colors?"

I think it is that the Cam itself can see in many colors including those beyond human sight.

Several images are taken with different filters to create a single color picture.

But because of payload limits, and design factors not all possible filters could be installed.

The real questions are will we see 'true' color images, and why has NASA not made it clear that the so-called color images are no such thing.

Originally posted by ArchAngel
The real questions are will we see 'true' color images, and why has NASA not made it clear that the so-called color images are no such thing.

They arent far off really.

I think I used the word filter too many times in my above post. Let me explain briefly.

Its not a matter of the pics being 'filtered' to remove a color range or anything like that.

Digital photography in the Pancam works like this. The CCT that 'takes' the photo can only interpret brightness levels (black and white). So photos are taken as a 3-part series. One image with a red filter, one with a green, and one with a blue. These images are then merged (as red, green, and blue) channels to form the digital images we see. This is done to get the highest possible resolution and quality.

As mentioned earlier, standard RGB wavelength values are 600, 530 and 480nm respectively. This corresponds to the L4, L5 and L6 filters on the Pancam. But, many pictures will be taken replacing the L4 with the L2 filter, which is set at 750nm.

This has all the above effects, including a seemingly less red environment. However, it is near infra-red and the pigment used on the blue color-chip is designed to be bright at these ranges as well as 480. As Dr. Bell has mentioned.

The obvious reason for using the L2 instead of L4 for red channel imagery. Is that when using L4, any light coming in between about 610-750nm is lost. These spectra may be very useful in giving more definition to areas in shdow. Especially red shadowed areas. We can still find out when pictures are true color or not by the raw images directory.

If a composite has been made of L4, L5 and L6 its 'true color'. That is, the setpoints used to take the picture are the same as the ones used to display it.

From earth it seems red yes but that is simply because of the rust, copper,etc. that make up the majority of it's surface. IMO the surface would seem brownish in color if I were to walk about it. The atmospheric conditions could also alter the way the planet looks from our surface here on earth.

This should add some fuel for discussion: (source: www.lunaranomalies.com... ) And, for a balanced alternative PDF From Sky & Telescope Seems like this will be a discussion for some time.

Ok, Just been put onto this thread and have read with interest. I have just looked at the NASA site and have come accross these three images in the RAW folder that would seem to indicate the L4, L5 and L6 filters applied.

Kano, can you do some trick with these?

marsrovers.jpl.nasa.gov...
marsrovers.jpl.nasa.gov...
marsrovers.jpl.nasa.gov...

There is also the coresponding right camer lens photos and images with filters L1, L2, L3 and L7 on the same page.

marsrovers.jpl.nasa.gov...

Thans swin, I actually downloaded almost all the raw images last night. Was really late when I started working with them, was having some strange results though. Going to go grab a beer and sit down to slog at it a while. Stay tuned.

Well, I may know PC's but I'm no artist so I have never really used image editing packages, yet the result I got from Kano's overlay method seems a little bleak.

Maybe it was raining- joke.

Mars true Colour?




[Edited on 13-1-2004 by swin]

[Edited on 13-1-2004 by swin]

That isn't true color either, thats what was stumping me last night. I finally figured out why by checking a few things on images taken on Earth. Explanation to follow.

BTW Did you follow the above instructions or did you already know what to do (I wasn't sure if I made the instructions clear enough)

I went through Wgatensons link of the Mars pics and found an anomaly. I have included a pic and a link to the original page. Does anyone have any idea what this could be?


Original link------>spacefinder.tripod.com...

It�s definitely metal and looks man-made. A cylinder with a slot running through the side from end to end. The far right side of the object looks as if it�s a curved plus sign. WTF is this?

Ok, here we go.

Firstly, I made a rookie error earlier in assuming simple combination of the RGB channels would be accurate. I overlooked one important fact.

Channels Normalized.
All three channels have been Normalized. More than that even, all three channels have been amplified to their absolute peak. I don't know the graphical term for it, the Audio term is Hard limiting. So I'll use that.

Basically, in each of the three filter pics. The exposure has been set so the brightest part of the picture from each filter, correlates with the absolute maximum brightness for that channel. For example the brightest part of the red channel is FF0000, green is 00FF00, and blue is 0000FF. (Obviously they all come in as b/w pics so in each black and white plate there is a perfect range from 000000 (absolute black) to FFFFFF (absolute white).

You can test this by opening one of the black and white plates (photoshop again sorry). Select either 000000 or FFFFFF as the working color. Then go to the select menu and color range. Set fuzziness to zero and OK. For each extreme you will find at least a few pixels of each.

On Earth
You can test the counter to this theory with a photo taken on Earth. Choose any photo taken on earth, (A good one to try is that Autumn road kinda one that comes with Windows XP). Open it in photoshop and set its blending options so only the blue channel is showing. Its very dark, and there are no 0000FF pixels at all. In fact there are only a few 0000AA pixels, and they are in the whiteish parts. You can try this with any picture taken on earth. Try to avoid pictures with solid black and white in them however. Or something silly like a rainbow. White requires bright amounts of all RG and B to show. The rainbow is self-explanatory .

Reason
Now, the reason for this at first is not immediately apparent. Why send the images in this form? The answer is simple. More data.

By sending each plate of colors spread across each extreme, you gain the maximum amount of data from each plate. Once you know the calibration information it is easy to amplify* each channel back down to its correct setting, and get the images looking as they should. If you were to send the images at equal levels, the blue channel would be sending a lot of information but not a lot of working data would be contained. It would be a fairly dark picture, why not have the exposure a little higher on the L6 filter images, and pick up all you possibly can from the surrounds.


It took me a long time to realise the answer had been staring me in the face, apologies for the delay. Unfortunately, this means it looks like it will be very hard for us to recombine the images into their actual true-color appearances. At first I thought it would be as simple as checking what changes were required to make the sundial show up correctly, then applying them to the other pics. This in retrospect (!) was a dumb idea from the beginning, as obviously an image that shows the primary colors (and white and black to boot). Would require the full range of all channels. So the channels will be pretty much equal.

Now, a way to test this. Is to get these images:
marsrovers.jpl.nasa.gov...
marsrovers.jpl.nasa.gov...
marsrovers.jpl.nasa.gov...

You will have to shrink the first one from 1024 to 512. The 'EFF' is a prefix for 1024x1024 and 'EDN' is for 512x512. I don't know why, thats just the pattern I've noticed . These are the 3 plates that make up the top of the little silver pole and corner of the sat-dish visible in the panorama.

marsrovers.jpl.nasa.gov...

Now, this pole has white (or very close) and also areas very close to black. So in theory all 3 channels should be close to natural.

Combining them in photoshop. (In the manner mentioned before. We get:


Which is extremely close to the colors in the panorama.

Yet when we use other 3-plate series from Sol05 (which is largely the panorama). Such as these ones:
marsrovers.jpl.nasa.gov...
marsrovers.jpl.nasa.gov...
marsrovers.jpl.nasa.gov...

We get:


A completely different look. Even though they are combined in the exact same manner. This is the effect of having all channels Hard Limited. You can re-create this effect by choosing auto-colors in Photoshop. While this is often handy, brightening up images and so forth. It does not work well when you are dealing with images predominantly one color, and whos brightest and darkest point is not a shade of grey.

How does NASA do it?
Well, clearly high-end, purpose made image processing software is a big part of it. It may also be possible that information about the series is contained in the filename. Or in other data transmitted by Spirit. I will continue trying to figure out if any part of the filename correlates to the exposure for that plate. Its a rather imposing filename though

Are we boned?
Not at all. Any picture with White and black, or bright red, green and blue in it will look almost exact when mixed evenly. What is the one thing we know has these? The sundial.

So any photo of the sundial. (Such as the ones shown earlier in the thread). We can be fairly sure will be accurate when mixed evenly. The convenient thing with the sundial is the fact it has mirrors on it to show the Martian sky, so with any plate-series of L4, L5 and L6 filtered plates, we can see the true color of the Martian Sky.

For example:


We can see the sky color in the little mirrors at the edges of the sundial.

Now, the one flaw with all this is the fact that a slight and constant hue of any sort would be removed by the equalisation of all the channels. So if anything all these pics would likely have a slight red/orange tint.


Now, I have an insane amount of random images clogging up my computer now, all in various stages of being fiddled with. Two interesting (and relevant) comparison ones are these:

There is a series on sol 8 (some of which swin pointed out) which looks like a test of almost all the filters at one hill. This was good news as it allows us to compare the difference when we use an L2 filter as the red channel and when we use an L4 filter.

The results are below.


The slide on the left looks less-red than the one on the right. Obviously the channels are normalised so the colours are not true. But it is a good visual example of the idea that the near-infrared selection of filter for the Red channel will actually give the appearance of less red than would using the L4 filter for the red plate.

More updates tomorrow night, need to find if its possible to get the exposure setting for each plate.

[Edited on 13-1-2004 by Kano]

Other conspiracy websites just sit back and theorize on what-ifs, how-comes, and why-fores... but none can stack up to ATS. Why? Well... we have Kano!

A couple questions...

1.You are Ansel Adam's grandson aren't you?
2. Do you work for a living?!

In all seriousness this is EXCELLENT WORK! I am AMAZED at how you have nailed this to the wall.

OUTSTANDING!

PEACE...
m...

Stating the obvious here, you seem to have a blue sky in every reconstruction, do you think this is acurate?