Hacker News Reader

Comment by Jiocus | Hacker News Reader

Artist James Bridle calls them "Rainbow planes" and has used this in his art.

Rainbow Plane 002: Kiev. October 29, 2014: https://booktwo.org/notebook/rainbow-plane-002-kiev/

Rainbow Planes: https://www.flickr.com/photos/stml/sets/72157637938061015/

“Rather than taking a photograph, satellite sensors record electromagnetic radiation in the red, blue, green, and high-resolution panchromatic (black-and-white) bands (as well as several not visible to the human eye, as this Mapbox[2] post helpfully explains). When these bands are combined to produce a visible image, fast-moving objects – like planes in flight – don’t quite match up, producing the rainbow effect.

[2] https://blog.mapbox.com/putting-landsat-8s-bands-to-work-631...

> Rather than taking a photograph, satellite sensors record electromagnetic radiation in the red, blue, green, and high-resolution panchromatic (black-and-white) bands (as well as several not visible to the human eye, as this Mapbox[2] post helpfully explains). When these bands are combined to produce a visible image

That's the same as taking a (normal, digital) photograph (sans additional non-rgb layers), just explained.

The difference is typical digital cameras have a bayer filter in front of the sensor to allow taking a single color picture vs. here it sounds like multiple captures with individual filters (e.g. 1 blue, 1 red, 1 green, 1 monochrome) that are later combined into a color picture.

The point was at all color photos record electromagnetic radiation in visible colors.

The “it doesn’t take photos it record electromagnetic radiation” is a silly thing to say.

This could be a comparative description of digital vs Chemical photography

Both are still capturing light.

"Chemical" photography captures electromagnetic radiation as well, but converts it into bonding energy, not into electrical signals.

There's some subtlety here. Colors are percepts- phenomena that happen in the brain. Wavelengths and radiation describe natural electromagnetic phenomena, not percepts.

Example: Infrared has no "color". It's possible to induce the illusion of colors in the absence of light altogether. I appreciate that the article took care with this language, as it's a deep and fascinating topic.

Reminds me of when Russia tried to blame Ukraine for downing the MH17 by producing a satellite image of the plane being chased by a jet fighter and even capturing the moment of launching the missile. Of course none of the moving objects had any sign of the color shifting.

https://nationalpost.com/news/russian-satellite-image-of-mh1...

Well it's a b&w image so...

Does anyone have a theory on why some photos have a rainbow plane and a solid white place offset?

They take a separate high-res monochromatic picture. (As image compression theory tells us, if you can afford to sacrifice some colour resolution for monochromatic resolution -- do it.)

It's interesting how some satellites take the alpha channel pic before the RGB channels, and some do it after. The lag also changes. Alpha & RGB have similar lags for some, but alpha is way off on others.

What does alpha channel mean in this context? Usually it means transparency but how would you take a picture of that?

Do you mean luminance? Alpha usually refers to the transparency channel in an RGBA image.

Whereas I believe you're describing more of a YUV setup

Reply on news.ycombinator.com