False colour composites were something I was introduced to in high school GIS and did a lot of in undergrad remote sensing. It was one of those <i>Eureka!</i> moments for me in terms of developing a better understanding of signals and signal processing, as well as sensors and data collection. Ie. absorbing the reality that the way in which my eyes (or any optical sensor) see the world is not canonical. <i>Vegetation is red, not green!</i><p>It was also just the COOLEST THING EVER to swap infrared bands in LANDSAT ETM+ imagery and watch vegetation immediately pop out at you. It's what turned this sort of dull (at least for a teenager) geoscience into a kind of puzzle where you have to figure out how to bring the signal up out of the data.
> False colour composites were something I was introduced to in high school GIS<p>As an old guy, this is something I'm jealous of in a positive way. I'm impressed that schools are offering this type of subject. My senior year was the first year to introduce a "computer science" class where I learned PASCAL on an Apple SE/30. The year after I graduated, the school created an actual computer lab. To be honest, I haven't even thought about looking to see what is available in schools today, but nice to hear something positive
I want to share a bit about this becuase it is dear to me.<p>My public high school was a "Geography / GIS magnet school" because some unnamed retired geography teacher donated a very large sum to make it happen. I was an underachieving student with no ambitions to go anywhere, doing just enough to pass. The geography program teacher pulled me aside and encouraged me to sign up for Grade 10 GIS the next year. It became my first academic passion and my entire life pivoted.<p>I studied GIS/remote sensing every year. I participated in Skills Canada a few times, eventually going the full distance by winning gold at the regional and provincial levels. I was accepted to University for GIS/Remote Sensing. I earned a BES, defended a thesis, earned an MSc, won a national award for GIS, and got into remote sensing + robotics as a career, which I'm still doing ~15 years later.<p>I don't think I have the words to really describe just how thankful I am for everything teachers and professors did along the way to support and encourage people like me.
I had a math teacher do something similar. He recognized that I was avoiding things by hanging out in his classroom. He decided that if I was going to stay in a maths room, I "clearly wanted to learn more maths" so he taught me more maths. And I soaked up as much as I could and it set me on a path as well. I'm thankful I had 3 teachers that took time and provided me that little extra that lasts a lifetime
My kids follow STEM here in Belgium, and there were multiple times when I thought "If only I could do those things when I was young".<p>At 12 years old, they get an Arduino and start programming in C. Then over the years they do all kinds of interesting things with it: build a car with controlled acceleration, build a tiny house with all kinds of sensors and controllers, monitor algae breeding.<p>When my son was 16, they brewed their own beer (Hey, it's Belgium and they can legally drink at 16 :D)<p>Now in the final year, they can propose their own projects. I heard previous years did things like create their own windmill and analyse the efficiency, electric generators in rain drainpipe, etc.
And, insects see flowers (and each other) differently than we do, as they are senstive to different parts of the spectrum, specfically ultraviolet. They see patterns and markings that are not discernable to human eyes.
While it hasn't been updated in a long while (2009)... Flowers in Ultraviolet
<a href="http://www.naturfotograf.com/UV_flowers_list.html#top" rel="nofollow">http://www.naturfotograf.com/UV_flowers_list.html#top</a> and <a href="http://www.naturfotograf.com/uvstart.html#top" rel="nofollow">http://www.naturfotograf.com/uvstart.html#top</a> (note: I'm looking into an old frames site - the proper page is <a href="http://www.naturfotograf.com/index2.html" rel="nofollow">http://www.naturfotograf.com/index2.html</a> ... and while its tangent to this, the reason I know of the site is drooling over large aperture lenses <a href="http://www.naturfotograf.com/need_speed00.html" rel="nofollow">http://www.naturfotograf.com/need_speed00.html</a> )
Also birds.
It's really fun to play with black and white photography using various kinds of color filters and see how different you can get the same scene to appear.<p>(Also fun to play with a polarizing filter.)
in the same vein, most high-end astrophotography imagers use B&W CCD sensors. Instead of dividing the pixel count by the RGBG layout, you get the full sensor worth of pixels. Different filters are used and then recombined using false color merging. Also, high-end motion film scanners using B&W CCD sensors using RGB filters so that each frame of film is scanned 3 times.
> Ie. absorbing the reality that the way in which my eyes (or any optical sensor) see the world is not canonical. Vegetation is red, not green!<p>Pretty funny to figure out that your perspective wasn't objective reality and then immediately decide to canonicalize another arbitrary reality as the One True Reality.
You can do something similar in GIMP:<p>1) Colors > Components > Decompose > LAB<p>2) For the layers of the A/B (chroma) channels, Colors > Levels > "Auto Input Levels" (maximize the contrast), and move the mid point to the median.<p>3) Colors > Components > Compose > LAB
That is very clever, thank you. Didn't even consider that yes, the contrast of the A/B channels is also the spread across the colour spectrum. Shows how little I use LAB... thanks for the reminder.
Can you explain 2 a bit more? I see the Auto input levels but unsure what you mean by "move the midpoint to the median."<p>The result I got for the original mars image was a washed out red image with some yellow around the craters.
I interpreted that step as "once you click 'Auto Input Levels', drag the center triangle of the 3 at the bottom of the histogram to where you think the median of the histogram is". That middle slider defaults to being the midpoint of the other 2 sliders. I'm not sure if there is a smarter way to move it to the median beyond "looks about right".<p>I got this as a result <a href="https://i.imgur.com/RsXx3y2.jpeg" rel="nofollow">https://i.imgur.com/RsXx3y2.jpeg</a> and it certainly doesn't preserve the color of the rest of the image (there are probably more algorithmic steps needed for that) but it does seem to make highlight the same faint patterns much more clearly.
The levels tool maps a subset of the channel range to the full range, effectively changing the brightness and contrast in one step.<p>The center point controls the gamma correction, so you can map a biased distribution (mostly bright or dark for example) to be more evenly distributed.<p>That was the purpose of that step - move the midpoint slider to about where the peak in the histogram is, to get an evenly distributed range.<p>The low/high slider can be moved towards that to increase the contrast.<p>"Contrast" here will only apply to the A/B channels, which is the color information, so it's increasing the color contrast and unbiasing it, while keeping the luminance information.<p>Photoshop also can do the same transform, and interactively in the LAB colorspace (no need to combine/uncombine the channels first).
Thanks for the details but I realized I should have said "Pretend I just installed GIMP and my knowledge of image editing is MS paint."<p>This is what I was after: "move the midpoint slider to about where the peak in the histogram is, to get an evenly distributed range."<p>It kinda worked! Thank you and sorry for making you explain the gory details though they are appreciated and useful.
Have you validated that it produces similar results?
My first thought reading this headline was "Really? Nobody thought of this until now?" But reading further, the Dstretch plugin has been around since 2005 or so. And presumably people have been using contrast enhancement, color manipulation, multispectral imaging, etc. to uncover hidden images long before that.<p>So not exactly "news" at this point. But still a pretty cool success story.<p>It almost feels like a feature that should be built into the default camera app. For anyone wanting to conduct their own forensic analysis to determine how thoroughly their hotel room has been cleaned, for example (although personally I'd probably rather not know).
I'm surprised this is getting so much coverage; This is well known from medical imagining and whatnot, that you take a black&white/limited gamut space and spread it to the full perceivable gamut.
I tried to look for hidden rock art at Ankgor Wat by imaging with multiple bandpass filters and amplifying cross-spectral differences. I didn't succeed, but maybe I was in the wrong place. The shit guards there also didn't like me using a tripod while I changed filters, so it was also hasty.
If it makes you feel any better, I've also never had any luck finding hidden rock art, petroglyphs, or similar using multispectal bandpass filters <i>or</i> decorellation stretching.<p>I was super excited about DCS based on some of the recovered petroglyph photos online, and integrated it into some software I wrote years ago.[1] Still hoping I find something as interesting with it as the fellow mentioned in the article. It works, but I haven't had a "gosh, I never would have seen <i>that</i> without DCS!" moment.<p>[1] <a href="https://www.beneaththewaves.net/Photography/Decorrelation_Stretch_Images.html" rel="nofollow">https://www.beneaththewaves.net/Photography/Decorrelation_St...</a> / <a href="https://www.beneaththewaves.net/Software/The_Mirrors_Surface_Breaks.html" rel="nofollow">https://www.beneaththewaves.net/Software/The_Mirrors_Surface...</a>
Sounds like they were the opposite of shit if they noticed someone setting up specialist equipment. I don't think any national monument in the world would be keen on people doing that without advanced permission.
>But it’s also due to the chance intersection of one man’s hobby with his unrelated professional and educational background.<p>I wonder how many great inventions can be traced to this type of circumstances. I suspect more than we realize.
“No one really knows why people made the rock art they made, at least in many cases,” Harman said<p>Well, it's obvious they really wanted to though. This isn't like marking on a wall with a Sharpie. They had to work at it to make it happen. The commitment alone is impressive even if it was just a "Grogg was here!"
Decently intentional and deliberate in many if not most cases. There are examples of it in high up places along sheer cliff walls in Arizona that boggle the mind trying to figure out how they managed to accomplish it and at the scale they are, then there are cave paintings that are hundreds of meters deep inside narrow caves in Europe.<p>It actually makes me wonder if this technique would produce any results in the notorious Erdstalls in Germany. I suspect not, but no one has any better ideas, so it might be worth checking.
<a href="https://smbc-comics.com/comic/rite-on" rel="nofollow">https://smbc-comics.com/comic/rite-on</a><p>> "No matter what you do, when we find something weird in ancient history we will decide it must've been part of a fertility rite."
Is there an imagemagick implementation that I can just throw into the pipeline?
DStretch is also really great at revealing painted ghost signs on old buildings.
See also: Eulerian Video Magnification (EVM) to amplify subtle motions and colour changes:<p><a href="https://youtu.be/ONZcjs1Pjmk" rel="nofollow">https://youtu.be/ONZcjs1Pjmk</a>
<a href="https://youtu.be/_qtzWNZApsw" rel="nofollow">https://youtu.be/_qtzWNZApsw</a>
Very Cool! I have a lot of 40MPx RAW pictures from the almost unreadable historic written walls in Delphi, Greece.<p>Let me test this with them.
Amazing. This will change how I take photos
any repo or link where other people can try?
Matlab - <a href="https://www.mathworks.com/help/images/enhance-color-separation-using-decorrelation-stretching.html" rel="nofollow">https://www.mathworks.com/help/images/enhance-color-separati...</a><p>This paper might also be of interest - <a href="https://www.mdpi.com/2227-7390/13/20/3297" rel="nofollow">https://www.mdpi.com/2227-7390/13/20/3297</a><p>"In this paper, we review the theory behind decorrelation stretch and propose some alternative algorithms that resolve the issues of the standard approach."
Had an llm build something quickly so I could play with it. <a href="https://shannietron.github.io/decorrelation_stretch/" rel="nofollow">https://shannietron.github.io/decorrelation_stretch/</a>
The app is called DStretch, it's available for iOS and Android<p><a href="https://dstretch.com/Apps/index.html" rel="nofollow">https://dstretch.com/Apps/index.html</a>
This supports something similar (PCA color stretch)<p><a href="https://meesoft.com/Analyzer/" rel="nofollow">https://meesoft.com/Analyzer/</a>
There is also a 21 euro app
<a href="https://play.google.com/store/apps/details?id=com.dstretch.androiddstretch">https://play.google.com/store/apps/details?id=com.dstretch.a...</a>
"A contribution is mandatory before I will send the plugin. It may take me a few days to respond, have patience.
Please note that the plugin is not an app. It has much more functionality than is possible in an app on a smartphone."<p>"The DStretch [mobile] app is a lightweight version of DStretch intended to give users the ability to enhance rock art in the field. It is not a substitute for the DStretch plugin which has much more functionality."
This is based off a NASA article, which has an expanded version with more details here:<p><a href="https://spinoff.nasa.gov/Manipulating_Satellite_Photos_Now_Reveals_Ancient_Images" rel="nofollow">https://spinoff.nasa.gov/Manipulating_Satellite_Photos_Now_R...</a>
The 1996 paper mentioned in the NASA article: <a href="https://dstretch.com/DecorrelationStretch.pdf" rel="nofollow">https://dstretch.com/DecorrelationStretch.pdf</a>
Updated from <a href="https://gizmodo.com/this-nasa-color-trick-was-meant-for-mars-now-its-unveiling-rock-art-on-earth-2000809844" rel="nofollow">https://gizmodo.com/this-nasa-color-trick-was-meant-for-mars...</a>, thanks!
Way better, thank you
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