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None of the pictures taken by Chang'e-4 Chinese lunar probe (see the attached images) in January 2019 have colors similar to the photos taken by Armstrong, Aldrin and the other 10 astronauts. The question is why?

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enter image description here Source

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    $\begingroup$ There should be a color calibration target with some precisely known colors as well as some neutral grey fields on the lander or rover. $\endgroup$ – Uwe Jan 6 at 13:33
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    $\begingroup$ @Uwe I guess the camera's properties are known to the operators and thus they could transform it to human perception as far as possible if they decided to do so. $\endgroup$ – Everyday Astronaut Jan 6 at 19:18
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    $\begingroup$ if you have something to say about your question being deleted feel free to vote, comment, or write an answer to Why delete a question with so many well-written and received answers? $\endgroup$ – uhoh Jan 7 at 9:08
  • $\begingroup$ I am not sure it fits. Therefore just a comment. We can easily see the real colour of the moon by watching the edge of its light filtering through the clouds when it is high in a cloudy night. It is indeed a dirty amber colour. $\endgroup$ – Alchimista Jan 8 at 15:36
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The moon is orange, not white. It looks mostly white for two reasons

  1. lack of a good white-balance reference
  2. our spectral sensitivity is fairly well peaked near 500-550

But it's not quite that orange, so what else could it be?

If one put scientific or technical cameras on the Moon at great effort and expense, one might not be as interested in using a standard Bayer color filter (R, G, G, B) to emulate human spectral sensitivity to make things look "normal" as one might be interested in collecting as much spectral data as possible.

If they used RGB or other color filter schemes, they might choose more widely spaced peaks in order to make the images more sensitive to spectral differences of different minerals especially if one were visiting a totally new hemisphere of the moon where no mineralogical investigations had been done at close range before.

There is no reason to expect the lander or the rover's camera to exactly replicate human vision, and every reason to expect it to have extended spectral sensitivity. The wider your red and blue-assigned filter peaks are from each other, the bigger the difference will be in the reflectivity of the lunar regolith, since it has such a characteristically sloped spectral albedo.

Below is borrowed from Why doesn't a full/gibbous moon high in the sky ever seem to look orange? Shouldn't it?

The internet goes a bit bonkers when human-perceived colors are assigned to camera spectral bands that don't match up. Answers to Is the “Mars blue dune” actually blue? And what makes it so? points out such a situation, where the "red" channel is completely in the near infrared.

That's an excellent example of mapping the spectral channels of a mineral-sensitive spectrally-extended imager on to human colors producing artificial colors.


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above: "Figure 8: Averaged geometrical moon albedos measured by GOME from July 1995, November 1995, and September 1996." From ESA's GOME moon measurements, including instrument characterization and moon albedo.

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That's due to a difference in color balance. The Chang'e 4 images look like they haven't been calibrated yet.

Cameras on spacecraft often don’t see colours in the same way as the human eye. For example, the red, green and blue components are usually recorded separately. This was the case with the latest images, and no colour correction has been applied to take account of the different sensitivities of each set of the camera’s colour detectors.

The first picture below is an example of one such “raw” image, and I’ve accompanied it with histograms of the red, green and blue channels to show how brightness is distributed in each. In the raw version, the lunar surface looks red because the detectors used were more sensitive to red than they were to blue or green. So although in truth the surface is almost equally bright in all three colours, the green and blue detectors have been set up so as to be less sensitive to light than the red detectors. This is why the green and blue histograms do not extend to the bright end of the range of their scale.

So how can we be sure of the colour on the moon? When the Apollo astronauts took their colour photographs (and in those days it was photography, using colour film, rather than digital imaging like today), they placed a colour calibration target containing patches of known colour in the field of view.

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(Apollo 17 photo with calibration target)

It is a pity that CNSA did not add a colour calibration strip onto the ramps of the Chang'e 4 lander, in the foreground of the pictures above. ...

However, the images from the Chang'e 4 lander and the Yutu 2 rover are primarily for navigation purposes, for which getting the colour right scarcely matters.

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    $\begingroup$ How did they calibrate the Apollo pictures? $\endgroup$ – Robert Werner Jan 6 at 12:54
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    $\begingroup$ @RobertWerner that would be a great question to ask as a separate question. You can link it back to here to maintain continuity. $\endgroup$ – uhoh Jan 6 at 13:09
  • $\begingroup$ @Robert Werner Short answer is taking shots of a known colour reference and adjusting till that is the right colour. If you wanted to you could guess in the above photos that rover is pure white and tweak till the rover looked white/solar cells black and get close. $\endgroup$ – GremlinWranger Jan 6 at 13:31
  • $\begingroup$ @GremlinWranger The rover is so overexposed as to be fully saturated in all three channels. No amount of tweaking will change that. $\endgroup$ – Michael C Jan 10 at 4:37

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