South from the landing site, sols 72-237, Starting the science traverse Options

[Bill Harris]

When you find something about how the auto white balance works under martian conditions, please send a link.

Egads, "color balance" is a can of worms. It means precisely what you want it to look like. And auto white balance comes from an algorithm analyzing the RGB content of the scene and correcting it to whatever the developer thinks. As do the scene modes: sunlight, overcast, afternoon, tungsten or fluorescent. JPL may have even set their own custom balance using a Martian McBeth Card.
Let me make a discrete exit by dropping a Sony link:
https://helpguide.sony.net/gbmig/45349331/v...0000522853.html

[nprev]

ADMIN: Due to unacceptable, argumentative conduct by a member 14 posts--including knowledgeable and well-intended replies intended to correct several incorrect perceptions and assumptions by said member--hidden. Possibly more to follow.

EDIT: Removed 7 more posts in an attempt to make the discussion more linear. If I accidentally deleted anyone's post that they feel should be restored and preserved in context, please PM me.

Apologies for the entire debacle, which unfortunately lasted far too long. Even evil robots gotta work a day job.

[Bill Harris]

I've been flummoxed by the radial pattern, as as can be seen in this example reference earlier by Tau. I was losing too many synapses wrestling with the impossibility of radial abrasion, so perhaps the pattern is simply composed of remnant dust left over from the GDRT process?
snip

The abrasion bit is driven by a rotary-percussibe drill, and the abrasion bit has an "unusual tooth pattern: three parallel lines of different lengths, arranged asymmetrically. When the drill spins and hammers with an abrading bit, that tooth pattern creates crisscrossing, well distributed impactsin the rock".

Attached thumbnail(s)

 

[mcaplinger]

The Ingenuity color camera is an off-the-shelf Sony IMX214 camera module, which can be googled.

I haven't been able to find any specifics about the exact camera module being used, especially about the optics or the auto white balance settings/behavior. I'm fairly sure that however it's being operated, it wasn't custom-set for the expected martian lighting conditions. We saw a lot of weird white balance issues with the EDLcams also. I don't know how the RDR products are being produced for any of these cameras and I would take their color rendition with a grain of salt.

[Bill Harris]

Absolutely. Ingenuity is a technology demonstration and I don't expect a miraculous color camera setup. And there have been weight, size and other constraints with this camera, so all things considered it has worked brilliantly.

--Bill

[JRehling]

It's been discussed on here many years ago, but "true color" is somewhere between hard to come by and absolutely nonexistent. The spectrum of martian daylight is certainly variable depending upon latitude, altitude of the Sun, and multiple parameters of atmospheric dust over a given time and place. A three-color camera (or our eyes) loses information regarding the fine details of any given spectral curves, and creates ambiguity between, to pick one example, narrowband yellow on the one hand vs. the sum of narrowband green and narrowband red on the other. The number of nonlinear interactions is boundless and that's even before the important matter that mcaplinger mentions of white balance in an off-the-shelf system.

VIMS on Cassini is an example of a multispectral imager that was designed to return data that could be used – in ideal cases – to constrain the composition of the surfaces that it imaged. That isn't the objective or design of every camera, nor should it be.

[James Sorenson]

The post-drive Right-eye Navcam pan from Sol-210.



Polar

[Phil Stooke]

Very nice, James. Here is a version in my circular projection - more compressed towards the middle, stretched radially at the horizon.

Phil

[tau]

It's been discussed on here many years ago, but "true color" is somewhere between hard to come by and absolutely nonexistent. The spectrum of martian daylight is certainly variable depending upon latitude, altitude of the Sun, and multiple parameters of atmospheric dust over a given time and place. A three-color camera (or our eyes) loses information regarding the fine details of any given spectral curves, and creates ambiguity between, to pick one example, narrowband yellow on the one hand vs. the sum of narrowband green and narrowband red on the other. The number of nonlinear interactions is boundless and that's even before the important matter that mcaplinger mentions of white balance in an off-the-shelf system. . . .

The question "What colors would we perceive if we were standing on Mars?" may not be answered until we are actually standing on Mars, because our visual system (eyes and brain) and digital cameras work differently.
For example, we cannot turn off our automatic white balance, which can be very confusing at times. An impressive example are the "gray strawberries". The effect is explained thoroughly with visual examples in this video (13 min).
Taking into account the gray-strawberry-effect, I would expect to perceive a less saturated and lighter red ochre / sanguine/ red chalk tone than in the calibrated natural color images, and would not exclude an apparently slightly bluish tint in our perception of some gray rocks.

[fredk]

To risk extending this OT discussion too far, that same auto-white-balance effect should also occur if you can view an image of Mars on a large enough display. A properly calibrated image in sRGB colour space, viewed on a well-calibrated sRGB monitor, should reproduce well the 3-stimulus you would have on Mars. It's the ambiguity that JRehling mentions that allows that to work (ie, you don't need to reproduce the full spectrum).

[Bill Harris]

It's been discussed on here many years ago, but "true color" is somewhere between hard to come by and absolutely nonexistent.
SNIP

In fact, the issue of "color balance" subjective and a matter of perception. And add to that the eyes will adapt to the color temperature of the light they are in. Sitting in your library, you don't see the warm tones of the tungsten lighting. Moving into your kitchen, you don't notice the bluish tinge of the LED lamps. Or stepping outside, the 5000*K of the natural sunlight. The eyes adapt.
Literally, color balance is what you want it to be.

[mcaplinger]

Not to give the mods too much of a workout, but this whole color discussion should be moved elsewhere.

[JRehling]

Agreed. I thought that the "true color" had already taken place somewhere, but I couldn't find it, or I would simply have linked to that.

[tau]

Some partially overlapping photos taken by Mastcam-Z on sol 207 at the same second allow a stereometric grain size analysis.
Most of the grains in this image are about 1.8 mm in diameter, which corresponds to a very coarse sand.
To get a real sense of the grain size, zoom in or out until the white bar is exactly 10 mm long on the display.
Between the grains is much finer material (dust?) that is too fine to be measured with stereometry.
To prove the calculation, I determined the diameter of the abraded depression in other sol 207 images,
and the result is 49 mm (4.9 cm), which agrees well with the 5 cm diameter of the abrading bit given by NASA.

[Bill Harris]

Tau, the typically assumed size of terrestrial volcanic ash is 1.5 to 2mm. We don't know any if the variables involved with the Martian ash size distribution, but your measurement does agree with the terrestrial size. We don't know with certainty about the composition of this soil.

--Bill