12 ms·
Interesting how the three separate R/G/B images are taken independently a few ~seconds~ milliseconds apart, with a different color filter placed over the image
by MontyCarloHall 5y ago
Interesting how the three separate R/G/B images are taken independently a few ~seconds~ milliseconds apart, with a different color filter placed over the image sensor.
I assume this is to maximize resolution, since no Bayer interpolation [0] is needed to demosaic the output of a traditional image sensor that integrates the color filters onto the sensor pixels themselves. As these satellites are not intended to photograph things in motion, the color channel alignment artifacts seen here are a rare, small price to pay for vastly improved resolution and absence of demosaicing artifacts.
[0] https://en.m.wikipedia.org/wiki/Bayer_filter https://en.m.wikipedia.org/wiki/Bayer_filter
- c54 5y agoYour guess is exactly right, this type of imaging is pretty common with satellite imaging for the reasons you mentioned. Scott Manley talks about it in this video iirc https://youtu.be/Wah1DbFVFiY https://youtu.be/Wah1DbFVFiY
- HPsquared 5y agoDoing it this way allows not only higher resolution, but you can also use different types of filter for specialist applications. Infrared for example, or some kind of narrow band pass filters etc.
- birdyrooster 5y agoUnless you aren’t military and then no infrared for you
- wantsanagent 5y agoOh? Planet offers infrared imaging to farmers.
- can16358p 5y agoI literally have a 720nm lowpass infrared filter in front of me for use in photography. Infrared imaging is not "military", it's public, common, and legal.
- dsl 5y agoI think what they meant is prior to the "digital farming revolution" if you called up a satellite/arial imagery company and requested anything other than visible spectrum, you'd not only get some strange looks - they'd also alert the government.
- urschrei 5y agoNonsense. Landsat 8 bands 5, 6, and 7 are infrared bands (5 is NIR, and 6 & 7 are shortwave or SWIR), and bands 10 and 11 are lower-resolution thermal infrared (TIRS). Source: http://www.usgs.gov/faqs/what-are-band-designations-landsat-satellites http://www.usgs.gov/faqs/what-are-band-designations-landsat-...
- agilob 5y agoThere is plenty of RGB planes on Google Maps https://duckduckgo.com/?q=rgb+plane+on+google+maps+!gi https://duckduckgo.com/?q=rgb+plane+on+google+maps+!gi
- ericbarrett 5y agoMy napkin calculations are that the three channels are ~10ms apart, given the bomber is 69 feet nose-to-tail* and an assumption of 400 mph velocity. * http://www.dept.aoe.vt.edu/~mason/Mason_f/B2Spr09.pdf http://www.dept.aoe.vt.edu/~mason/Mason_f/B2Spr09.pdf
- ATsch 5y agoI would assume that the plane or satellite moving affects this too, it's presumably being corrected but there might be some parallax.
- ericbarrett 5y agoYou're absolutely correct, but as the aircraft is much closer to the ground than the imaging satellite I disregarded it. Spherical cows and all that :) I'm sure a military analyst would do the calculations!
- deleted 5y ago[deleted]
- jcims 5y agoIt actually works out to be pretty close. A satellite flying ~17k mph at 250 miles altitude would largely have the same angular displacement from the ground as a plane moving 400 mph at 31,000 feet. Most satellites fly in an easterly direction, so the question would ultimately be what the inclination of the orbit is relative to the direction of flight.
- matbatt38 5y agoWell no the speed of the satellite is irrelevant there, the background is not getting distorded at all
- ericbarrett 5y agoThat's super interesting! I love this discussion. Would the satellite be that low though? 250 miles (400km) is still going to experience significant atmospheric drag. Fine for a cheap mass deployment like Starlink, but I'd expect an imaging satellite to be set up for a longer mission duration. Then again maybe the cost of additional mass for station-keeping is worth it for the imaging quality.
- goblin89 5y agoI wonder if there are ways to get superior (compared to Bayer) color images from conventional raw-capable monochrome digital cameras (like Leica Q2 Monochrom) in static scenes using similar workflows of taking three separate shots.
- skhr0680 5y agoSergey Prokudin-Gorsky‘s work shows both the benefits and drawbacks of the swapping filters approach
- Koshkin 5y ago[1909]
- MontyCarloHall 5y agoAbsolutely! [0] In fact, the first color photos in the world were taken this way in the early 1900s [1]: take three monochrome exposures onto black and white transparencies with R/G/B filters, and then project the three images together. [0] https://leicarumors.com/2020/01/29/color-photography-with-the-leica-m10-monochrom-camera-m10m.aspx/amp/ https://leicarumors.com/2020/01/29/color-photography-with-th... [1] https://en.m.wikipedia.org/wiki/Sergey_Prokudin-Gorsky https://en.m.wikipedia.org/wiki/Sergey_Prokudin-Gorsky
- goblin89 5y agoInteresting. Sadly, I believe the Photoshop approach would not produce a DNG file that you could normally interpret in a raw processor of your choice. Looks like pixel shift cameras (which apparently still use Bayer sensors, just moving them around, to debayer at capture time so to speak) is the most practical option at the moment. I’m curious if it is technically possible for a digital sensor to capture the entire light spectrum of the scene, without the need for RGB separation at any stage—similar to Lippmann plate[0]. [0] https://en.m.wikipedia.org/wiki/Lippmann_plate https://en.m.wikipedia.org/wiki/Lippmann_plate
- 5y ago
- aeroman 5y agoYou can use this difference in time to calculate the speed (although you also have to account for parallax for an aircraft) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6651096/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6651096/
- jerry1979 5y agoInteresting. A search for those gradients could help find all fast moving objects in the satellite images.
- IAmGraydon 5y agoNow that’s an interesting idea. Anyone care to spin this up?
- druadh 5y agoIs there a way to subscribe to comments? I'd love to see the result of this idea but am not savvy enough to spin it up myself very easily
- coldpie 5y agoClick the timestamp for the comment, then click "favorite", then set a reminder in your calendar to check your favorited comments (link in your profile).
- dzhiurgis 5y agoCan Siri work with whats in your copy/paste cache?
- hk__2 5y agoWhat do you mean by “copy/paste cache”? If you mean the clipboard history, there’s no such thing on macOS. If you mean the clipboard (= the last thing you copied), Siri can work with the Shortcuts app, which itself can read the clipboard.
- dzhiurgis 5y agoI mean like "create a reminder to check link from my clipboard tomorrow"
- 5y ago
- malfist 5y agoThis is what we do all the time for astrophography! We buy monochrome cameras without an IR filter and take 3 photos and recombine them.
- t0bia_s 5y agoShadow of this object is also distorted: https://goo.gl/maps/VWwtt1PbLJVkbiBS9 https://goo.gl/maps/VWwtt1PbLJVkbiBS9
- diggernet 5y agoThank you. I was wondering where that was. Now, can someone calculate the plane's altitude?
- willis936 5y agoThe shadow is about 2500 feet away. Judging from nearby houses the sun is probably about 15 degrees SouthEast of noon. 2500 ft * sin( 15 ) = 650 ft Someone should double-check my geometry though.
- mmaunder 5y agoAlso came here to discuss this. Super interesting opportunity to reverse what they're doing. Yeah I'd agree it's color filters which would avoid duplicating lenses (probably the most expensive component) or dividing the light energy. Filters would give you the most photons per color per shot. I wonder if the filters are mechanical or electronic somehow. As another commenter calculated, it's 10ms between shots, which is not that impractical to move physical filters around when you consider modern consumer camera shutter speeds of around 0.125 milliseconds max.
- mrcode007 5y agoDifferent wave lengths travel at different speeds through glass and air and focus differently even on the same lens when color photos are taken in the single frame. https://en.m.wikipedia.org/wiki/Chromatic_aberration https://en.m.wikipedia.org/wiki/Chromatic_aberration
- bragr 5y agoTrue but if that were the case here it would also likely affect the ground.
- trothamel 5y agoIs it possible this is a a pushbroom sensor, where red, green, and blue sensors are moved along the path of the plane or satellite that's taking the image? My understanding is those have a higher effective resolution than frame-based sensors, which would make sense here.
- bragr 5y agoSeems unlikely to me. With push broom, I'd think you'd get characteristic squishing, stretching, or skewing of objects in motion depending on whether the object was moving against, with, or perpendicular to the push broom path. In this case with the imaging satellite probably in polar orbit and the plane flying east, you likely see the plane horizontally skewed as each horizontal row of pixels captured the plane further east.
- kevin_thibedeau 5y agoThese are pushbroom linear sensors stacked up in the focal plane. The spectral channels are physically separated by larger distance than neighboring pixels in a Bayer grid. There is a time delay between each channel sweeping over the same location that gets corrected when the final imagery is aligned. The moving plane at altitude violates assumption of a static scene and exposes the scanning behavior.
- baybal2 5y agoI think modern satellites have matrix sensors
- kevin_thibedeau 5y agoIt depends on the satellite. Weather satellites in GEO do because they aren't moving relative to the surface and they have time constraints for scanning the full earth disc. Higher resolution imaging satellites use linear sensors. However, they use TDI imaging which at a low level makes them superficially like an area array with limited vertical resolution but the light collection is still fundamentally different.
- formerly_proven 5y agoIs the R/G/B separation greater because these sensors are built like TDI CCD lines? edit: Seems like pushbroom is the name for TDI when it's put in a satellite.
- Scene_Cast2 5y agoFor anyone wondering about what a pushboom sensor is - http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.72.124&rep=rep1&type=pdf http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.72.... Basically a 1D sensor that acquires a 2D image because the camera itself is moving. In this case, I'd imagine that there are 3 such sensors for RGB.
- chris_va 5y agoFWIW, depending on the satellite (this one is probably WorldView 3), there usually more like ~6-7 channels in the visible. It makes for easier top-of-atmosphere correction, and can be useful for things other than pretty pictures.
- _dv46 5y agoI grabbed my red and blue glasses because this vaguely looked like a 3D anaglyph to me, and while it's not the clearest such image, it definitely appears as a cohesive object hovering above a flat map. Further I zoom out, it definitely looks like it. Inadvertent byproduct of however this was photographed or stitched?
- threevox 5y agoThat's a lot of words to rationalize away what is very clearly and obviously a cloaking device at work!!
- deleted 5y ago[deleted]
- thot_experiment 5y agoFun fact: this is called a Harris Shutter effect when it's done for art purposes.
- 123anonanonanon 5y agoActually the camera is (assuming geostationary orbits arę not used for imaging) moving ar speeds much much faster than the plane
- abbassi 5y agoFirst RED, then BLUE, and last but not least GREEN!