Combination of the infrared images of Sol 616 with R4 (red), R5 (green) and R6 (blue) give as a pseudocolor photo after some color enhancement an interesting result:

the blue-gray sharpe edged small stones (probably some vulcanic material) found strawn around the Erebus site look quite different in infrared but not in the visual band. There are at least three destinct infrared signatures giving probably a hint on their origin and chemical composition.

Here, on the left an R2 (red), R1 (blue)-picture is shown with synthetic green chanal according to the visual color taken from an L4L5L6 image and on the right the R4R5R6 picture.

The original Opportunity photos were normalized using a circular mask to reduce the radial loss of brightness to the edges.

This pair can be seen on the right (I am wondering that the thumbnails are not shown in the correct sequence).

The second image couple shows Bounce at Sol 68 in L4L5L6, L2L7 and R2R1 (from left to right with synthetic green in L2L7 and R2R1) for comparison: There is a possibility to make nearly natural looking color composites using the R2 and R1 channels.

This image triple is shown on the left.

(Image processing was done by collegue Mr. Norbert Gasch)

The interesting question is now: Does anyone have an idea what sorts of material this can be at the Erebus site?

Best wishes: Harald

You're using the JPG's from Erebus I assume - and that's a fundamental barrier in making any spectral claims. It can not be done. You can fudge them to make pretty pictures, you can measure how far things are apart, but you can NOT under any circumstances, using any magical technique, use the raw JPG's to make any claims as to the spectral properties - even in just a relative sense - of anything imaged.

Doug

Doug: I'm guessing you are saying that because we have no idea of the exposure times used for the various fiters, and will not know until the PDS release of these images. Is there something else going on in the conversion to jpeg?

Because the individual exposures are unknown, we sure can't say much about the spectral properties, but it seems that within the confines of this particular set of images we can detect relative differences between the spectral properties of the various pebbles.

Harald's image from Erebus is interesting in that it seems to show several different types of pebbles, where they all are very similar in color, looking at the visual bands. I previously thought we were seeing only two different kinds of pebbles; the blueberries and the dark cobbles. But this false color composite seems to strongly suggest several distinct mineralogies/lithologies.

Harald: A long time ago, before I understood that the individual filters were imaged with different exposures, I tried to determine the mineralogy of the blueberries by sampling their luminance in all the filters, correcting them according to the quantum efficiency curve for the pancam CCDs and their predicted exposure times, as published in the Bell paper, and then comparing the derived spectra to published spectra of various minerals. It was a lot of work, and my results were inconclusive. After the announcement that the blueberries were hematite I could see some crude similarities between my spectra and those released by JPL in an early press conference, but nothing one could be confident about.

Thanks for sharing that image with us. I have to imagine you are seeing a real difference between the pebbles in that image, but I think we would need additional information to identify the minerals. But to be honest, I am not an expert in spectral analysis.

I propose a simpler explanation. The sun changed angles enough that different surfaces of the angular pebbles are brightly illuminated in the different exposures.

Harkeppler: I've gone to sol 616 on the rover web site (not exploratorium) and downloaded all the images for the L and R cameras, and then did several color composites based on different band combinations.

For my composites, I combine bands in the order (RGB) output = bands (abc) in put, where I list the bands in order at the end of the file name, always using long-wavelength as red and short wavelength as blue. I tweek the contrast with "curves" in photoshop to improve contrast on bright surfaces and do an edge-filter sharpening in "LAB" on the "Lightness" image so as not to add noise to the color variations.

The L: 234 image composites infrared,far-red,red as R,G,B and shows little color contrast at long wavelengths in the Left camera. The L: 257 images uses near infrared, Green, and Violet filters as RGB and gives similar results to the more natural color 456 combination, but with more contrast. L: 567 composites Green, Blue and Violet as RGB and shows short-wavelength color variations.

R: 654 composites the 3 right camera infrared channels you said you used and should approximagely produce the same result. I simply do not see the wild color variations of some of the blueberries you've produced. Nor do I see color fringes at the edge of shadows in your image that would result from significant sun movement between filters. (Shadow fringes would be small as the height of the shadow-casting edges is small)

I'm wondering if you may have found a set of images taken at the same sun angle and with the same rover position but on DIFFERENT DAYS, and the wildly colored blueberries could have had dust added or subtracted by wind during the interval between pictures. Otherwise, I'm wondering if your image processing program might have color or brigtness "keyed" on something by accident and generated these bizarre colors. Your Bounce rock images look perfectly reasonable, so I don't understand what may have happened.

Yes - they all get stretched to hell and back. Basically, it's like the 'auto-levels' function in photoshop - and once you have an image, you have no means whatsoever of converting it back. Not to mention the conversion from 12 bit to 8 bit, and heavy JPG compression.

It's not just exposure and stretching, it's all the other calibration that goes on ( flatfield, dark field, exposure, temperature etc etc etc ) that we only get with the PDS releases as well.

Doug

The problem item is the stretching\auto levelling because we have absolutely no idea what the conversion was doing at the time. The use of the jpg format also affects the usability of the data, I suspect that we could compensate somewhat for it but I would not trust a spectral interpretation from an image that had been jpg'ed.

The other conversions could be compensated for to some degree:
8->12bit. We have the look up tables for these so that's straightforward.
Exposure. This is slightly tricky but with the regular sun shots and fairly precise knowledge of the light model at any point in time it is be possible to get a fairly accurate estimate of the exposure duration of an image.
Temperature. This is harder to deal with but once again it can be estimated albeit with a fairly high error margin based on already published data.
The Flatfield\darkcurrent removal and other calibration steps seem to be sufficiently well documented to allow amateurs to carry them out if they had unmodified raw image data.

IF we had temperature, exposure and (all of) the unmodified raw image data then we could do the rest. But since we don't have that it can't be done.

All we actually need is an l/p to the recent data on the workbook

Doug

Your words are strong and absolute. Some people are very bright.

Because the matter is absolute. Fact.

You could be the most intelligent person on earth, but you cant get from those JPG's to any sort of calibrated product. End of story.

Sorry to be so blunt about it - but there are too many people claiming to do 'real' colour images using the JPL JPG's online, and it's missleading and uninformed to do so.

Doug

It's worth pointing out that this is at least the third time this has been discussed here in some detail. I was at least partially the cause of a previous debate on this and very much appreciate Doug's patience with those of us who have caused the debate to be revived.

It would be nice if future missions provided completely raw image data in some lossless format in addition to the "stretched for easy viewing" variety but for now we have to be content with just working with the pictures.

Well - we do get the proper data, just 6 month in 'back pay' as it were.

I must admit - I'd like to see that time come down - but I also know that the scientists and engineers who do the amazing job they do, deserve the first bite of the apple

Doug

This whole discussion reminds me of the net kook who insisted he had developed proof for his "c" theories about a specific manned launch disaster (that occurred just short of 20 years ago, you'll pardon me if I don't invite unwanted attention by mentioning him, or giving other specifics) by determining the elements within the fireball via spectral analysis of a VIDEOTAPE that he had of the explosion.

Yep -- he put a crude spectrometer up against his TV screen and claimed that the light recorded on the video signal contained all the original wavelengths necessary to do a proper spectral analysis of the fireball.

Funny thing is, he made a big deal out of all the phosphorus he saw in his spectra... *giggle*...

-the other Doug

To be fair, I don't think Harkeppler or anyone else made an outrageous claim here. In spite of the jpeg stretching, the lack of calibrations, etc... it seems perfectly reasonable to expect that relative spectral differences could be interpreted as differences in mineralogy within this image.

What is most interesting now is the fact that edstrick's work did not reproduce anything similar. I'd like to better understand why that is the case.

Yep, gotta agree. Harald made a decent effort to check something out in a methodical way and I wouldn't want him to think we were a bunch of arrogant wags having a go at his efforts. It was a good question just unfortunately based on untrustworthy data.

Since I made the same erroneous assumption myself in the past I have to say it's not obvious at all that the image data is modified before it's put online. It's glaringly obvious as soon as you try to do anything serious with them.