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Comment by elorant | Hacker News Reader

Why are most of the pics black and white?

See here: http://www.planetary.org/blogs/emily-lakdawalla/2015/0310163...

New Horizons is able to transmit to Earth at only about 2 kb/s (I might be slightly off). So right now, and for about the next week it will be sending back essentially thumbnail images (in addition to science data). These are JPEG-compressed, and during this stage will only be from the panchromatic (b&w) camera, which has a higher resolution. Later this year it will begin downlinking the full set of uncompressed, full-resolution images, including those in color. The full dataset is expected to be about 60 GB and will take about 18 months to downlink.

The camera is monochrome, another sensor gets "color" information. I think even the black and white images are not really "true" images since the sun is really really really far away (not totally sure about that though).

EDIT: LORRIs images are true, Pluto is actually pretty bright (the sun is amazing) and the camera is great (science is a amazing).

On Pluto, the Sun is 250x more bright than the moon is on Earth. And moonlight (at a full moon) is pretty sufficient for most things you do with your eyes.

http://blogs.discovermagazine.com/badastronomy/2012/03/15/ba...

That's because the human eye works across an amazing range of light intensities. https://en.m.wikipedia.org/wiki/Adaptation_(eye)#Efficiency:

"The human eye can function from very dark to very bright levels of light; its sensing capabilities reach across nine orders of magnitude. This means that the brightest and the darkest light signal that the eye can sense are a factor of roughly 1,000,000,000 apart. However, in any given moment of time, the eye can only sense a contrast ratio of one thousand. What enables the wider reach is that the eye adapts its definition of what is black."

Pluto is 30-50 AUs from the sun, so ignoring the effects of any atmosphere, there's "only" a factor of 900-2500 more sunlight on Earth than on Pluto (sun vs full moon is 400,000:1 or thereabouts)

Yeah, I was surprised about how bright the sun is on Pluto. Before this week, I thought that it was pretty much just starlight on Pluto with the sun looking more like Venus at night.

It turns out that the day on Pluto is like dusk on Earth. Check out this great page from NASA: it will tell you the time (for your location) where the daylight will be equivalent to the daylight on Pluto: http://solarsystem.nasa.gov/plutotime/

You can also see photos other people have uploaded, giving an idea of what Pluto daylight looks like. Surprising bright.

For me, it's something like 8:15pm when the daylight is equivalent to Pluto.

It can't actually take 'true' colour pictures at all --- RALPH has sensors in blue, red, infrared and methane, but not green.

I suspect they can probably synthesise true colour-ish by comparing the monochrome images to the blue and red ones; subtract blue and red from overall brightness, and what you have left is green (ish).

Enormously technical nigh-incomprehensible paper here: http://www.boulder.swri.edu/pkb/ssr/ssr-ralph.pdf

The highest resolution imaging system, LORRI, is monochrome. They can provide color by using another, lower resolution system named Ralph, or by any of a number of false color approaches. See more e.g. here: http://pluto.jhuapl.edu/Mission/Spacecraft/Payload.php

Honestly speaking, "colour" cameras we use every day are also false colour; they shoot 3 monochrome images in red, blue and green chunks of spectrum and mix the whole thing using plethora of parameters like white balance, or gamma. All this is heavily tuned towards human vision specifics to enable either monitor or print to induce a similar sensation in the viewer's brain that the photographed object would, despite the fact that the whole process retains only a negligible fraction of the information carried into the camera by the original photons. Quite a lot of animals perceive the hue of human-made photos and videos as totally odd, misexposed or desaturated, just because of having vision adapted to wavelengths or other properties of light which our processing mostly removes as redundant. Even more, one day humans may start to enrich their vision by technological or biological modifications, consequently beginning to perceive today photos as as dull as we see those old, monochrome ones.

The Foveon sensors are a sort-of exception to this rule, but they haven't really demonstrated enough visible benefits for them to become widely adopted.

To elaborate a bit, almost all digital cameras take a single monochrome exposure but each sensor element has either a red, green, or blue filter over it, in a mosaic pattern. From the relative brightnesses of neighboring pixels color data can be reconstructed and interpolated to form a human-viewable image.

That's how you get the highest resolution possible, all else being the same. Instead of having sensors for different light wavelengths, you just pack more of them.

If they had a bigger probe, they could have used color filters to take 3 pictures and then combine the resulting images into a single one with color information. Size and complexity constraints probably prevented that.

They have color filters. In fact the biggest single pictures are taken using the color camera.... in black and white mode.

The main limitation is time. They're blowing through in a couple hours. Monochrome data is faster data.

Because the instruments that took the pictures monochrome.

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