Are Mars images real color?

[Yora]

Supposedly, most photographs from Mars have a significantly more red shade than you'd get with a normal. Is that really the case? If so, what's the purpose?

I guess some older monochrome pictures were tinted with a shade of red that someone simply guessed would be similar to the real color. But there's also images with several shades of rocks and sky, next to color adjusted images with less red that supposedly are more accurate.

Anything to this?

[Fat Rooster]

Many of the historic images have been composites of multiple monochrome images with different filters, and those filters were not necessarily chosen to mimic the human eye. This has made producing images that are 'real' tricky, and in the past we have gotten it wrong (in both directions, for a number of reasons. Mostly that it is hard).

The current cameras are much smaller and lighter, so Percy is loaded with them. Some of them have specialised filters, but many of them are basically commercial cameras like you would have on a phone or go-pro. The question then becomes whether they are 'real colour'? Anyone who has tried to take a picture of a sunset knows how bad cameras are at capturing it here on earth, and the same is true on Mars. The best results use an AI post processor to 'touch up' the image, arguably making it less real (but looks closer). Try to put that through a screen with it's own colour distortions and things get worse.

The real difficulty is that when we see we tend to automatically account for many things we don't even realise, which makes capturing 'real' images significantly more challenging than many realise. If you can see a shady area as well as a brightly lit one, the brightly lit area could be 1000x brighter and you would still be able to see. That shady area is probably lit mostly by reflections, which may have a very different spectrum from the directly lit areas, making the colour very different even if the material is the same. We automatically account for this, based on experience and context. If you've ever turned on the 'night mode' on your computer you will realise just how much the colour balance can change without you having any issue. Even traditional photographs (which are able to get a large dynamic range and don't need a screen) will be dependent on ambient light conditions when viewed.

If you want to get a sense of the actual colour, you probably need to completely immerse yourself in the context, and switch between a calibrated Mars scene and calibrated Earth ones. We are very bad at understanding images objectively, but very good at comparison. Without something that we know about to compare it to, and Martian image is difficult to really understand.

[Eldan]

Yeah. In fact, I've seen at least one physicist sum it up as "there's no such thing as real colour". Even if you put the same camera you have on Earth on Mars, it would still be white balanced, colour corrected, etc. Then sent back to Earth and interpreted here. What your phone sees isn't what you see, either.

[Khedrac]

What your phone sees isn't what you see, either.

In fact this is probably the key statement. The human brain relies far more on expectation to assign colours than it does on visual signal received - and that's before you start running into tricks with ambient lighting.

[Radar]

In fact this is probably the key statement. The human brain relies far more on expectation to assign colours than it does on visual signal received - and that's before you start running into tricks with ambient lighting.

Pretty well known example of exactly the problem of context (or maybe background in that case?).

The brain is doing a lot of weird things with colors and one of the craziest is that we actually see colors in a rather narrow angle (the most extreme for red) - everything else is filled from memory in the same way as the blind spot is.

[Mastikator]

Mars photos are adjusted like that probably for the same reason space photos of nebula and galaxies are color adjusted: for clarity. Nebula aren't actually colorful to the human eye, they're dark. The color is added to indicate different elements, it's to give the viewer a better understanding of what they're looking at.

[Yora]

Yeah. In fact, I've seen at least one physicist sum it up as "there's no such thing as real colour". Even if you put the same camera you have on Earth on Mars, it would still be white balanced, colour corrected, etc. Then sent back to Earth and interpreted here. What your phone sees isn't what you see, either.

As long as a camera captures the light conditions on Mars with a comparable accuracy as we have in pictures taken from Earth, that's "real enough" for me.

[Fat Rooster]

Probably worth showing a picture of a colour calibration palette from curiosity. They learned from the mistake of not taking a calibration tool with them.

[Lord Torath]

Just for fun, here's a collection of photos from Perseverance on Mars: Raw Images.