• There is a problem with the forum sending notifications via emails. icerat has been informed. Thank you for your attention to this matter.

Pictures visible only through digital cameras - How does it work?

Towlie

ancillary character
Towlie
Joined
May 22, 2009
Messages
1,474
How does this work? I know infrared light that's ordinarily invisible, such as what comes from a TV remote control, can be seen through a digital camera, but how can the same effect come from artwork printed on a t-shirt? :confused:

http://gizmodo.com/gadgets/more-tha...y-visible-through-a-digital-camera-282689.php

Kameraflage Images Only Visible Through a Digital Camera

kameraflage.jpg


With Kameraflage, now you'll be able to plant subliminal messages on T-shirts, movies and billboards that can only be seen with digital cameras. This context-sensitive display technology, developed by Sarah Logie and Connor Dickie, works by using colors that are invisible to us but easily picked up by the cameras' silicon chips. As you can see, the lovely model above is wearing a shirt that only reveals that cloud's lightning bolt when seen through an iPhone's camera, although any ordinary unmodified digicam would get the same result. She just as easily could have placed her phone number in that cloud. Hmm. Let's think of some other uses for this cool tech.
Click to expand...
 
Point the IR LED from a remote control, such as one from a TV or VCR, at a video camera lense, and operate the remote's buttons. You will see the flashing IR lights in the video camera's display, but not in the real world.

The shirts and things work on the same principal. Cameras sense a different range of the elctromagnetic spectrum, than human eyes.
 
Infra-red reflective paint?

It's used to keep desert buildings cool during summer's heat. A side effect would be to brightly reflect the camera's IR range/focus feature.

I bought some surplus once to paint an old army truck. In 110° desert heat, the fenders were cool enough to sit a bare ass on with out leaving skin samples behind. You would think that Detroit could use that technology in vinyl seat covers.
 
casebro said:
A side effect would be to brightly reflect the camera's IR range/focus feature.
Click to expand...

It's a common misconception that camera's focus by sending out a signal to calculate the distance to the subject. They focus by using software to analyze lines within the picture.

Steve S.
 
Wowbagger said:
Point the IR LED from a remote control, such as one from a TV or VCR, at a video camera lense, and operate the remote's buttons. You will see the flashing IR lights in the video camera's display, but not in the real world.
Click to expand...
I use this to test the batteries on my remote controls.
 
steve s said:
It's a common misconception that camera's focus by sending out a signal to calculate the distance to the subject. They focus by using software to analyze lines within the picture.

Steve S.
Click to expand...

Point and shoot cameras tend to use active focusing. DSLRs use the passive method you describe. Some use both.

My SX100is uses passive focusing, but has an AF assist beam as well. In Auto mode it uses the beam when it needs to, in Program mode, I can turn the beam on or off.

Many cameras that use passive focusing still have an AF assist beam that helps out in the dark.

Canon EOS cameras will use the AF assist beam on the Speedlite flash if they need to, for example.
 
Last edited:
steve s said:
It's a common misconception that camera's focus by sending out a signal to calculate the distance to the subject. They focus by using software to analyze lines within the picture.

Steve S.
Click to expand...

Polaroid used to do this with an acoustic signal. This is why people think that. You could even buy development kits with the emitter/sensor and appropriate electronics to design your own applications for that part.

http://ltu164.ltu.edu/~mtedder/Polaroid6500_Sensor.html
 
BenBurch said:
Polaroid used to do this with an acoustic signal. This is why people think that. You could even buy development kits with the emitter/sensor and appropriate electronics to design your own applications for that part.

http://ltu164.ltu.edu/~mtedder/Polaroid6500_Sensor.html
Click to expand...
.
Thirty some years ago we (Lockheed Flight Test) looked into using one of those for getting precise measurements of altitude during the final phases of a landing.
I disremember why it was never done. Doppler problems, most likely, with the plane going 150 mph and descending.
 
Let's think of some other uses for this cool tech.
Click to expand...
Paparazzi-averse celebrities can paint their faces to look like Harvey Levin, or graffito themselves with editorial comments or obscenities...
 
Would these messages be picked up subliminally by humans, or just by the camera?
 
Fluorescent paints absorb UV light, and re-radiate the energy at a lower frequency in the visible spectrum.
I'd guess that they've simply shifted the frequency of re-radiation down even further to the IR. Wouldn't dast guess as to what frequencies they're absorbing.
 
LTC8K6 said:
My SX100is uses passive focusing, but has an AF assist beam as well. In Auto mode it uses the beam when it needs to, in Program mode, I can turn the beam on or off.

Many cameras that use passive focusing still have an AF assist beam that helps out in the dark.
Click to expand...

I wasn't talking about assist beams. Those are just there to illuminate the scene so the passive system can see better. It's not calculating distance by timing how long the beam takes to hit the target and reflect back.

Steve S.
 
bokonon said:
Paparazzi-averse celebrities can paint their faces to look like Harvey Levin, or graffito themselves with editorial comments or obscenities...
Click to expand...

'This photograph not for distribution'
 
steve s said:
I wasn't talking about assist beams. Those are just there to illuminate the scene so the passive system can see better. It's not calculating distance by timing how long the beam takes to hit the target and reflect back.

Steve S.
Click to expand...

IIRC, some AF assist beams just provide illumination, some create a pattern that the software recognizes, and some calculate the distance.
 
Towlie said:
Me too. It's funny that Wowbagger chose to repeat back to me essentially what I said in my initial post.
Click to expand...

hey, did you notice that wowbagger said the same thing as you did? :)

Looking into this technology, the only thing I could come up with was that stupid shirt. I smell a prank. I have seen shirts with LEDs embedded, maybe this shirt is the same with IR LEDs.

If you look at the last pic on this linky, it looks like there is something behind the shirt in the same shape as the image on the screen.

This pic is also telling as to the actual technology involved.

Now look again at the original picture
 
INRM said:
Would these messages be picked up subliminally by humans, or just by the camera?
Click to expand...

Yes, yes they would. The government is going to be using them against you soon.

Either that, or, of course they won't be. Any message, subliminal or otherwise, has to at least use a sense you possess already. Now if they were shooting thermal IR beams at us using Morse code to spell out, "Buy more Ovaltine," then that might work. :)
 
jasonpatterson said:
Yes, yes they would. The government is going to be using them against you soon.

Either that, or, of course they won't be. Any message, subliminal or otherwise, has to at least use a sense you possess already. Now if they were shooting thermal IR beams at us using Morse code to spell out, "Buy more Ovaltine," then that might work. :)
Click to expand...

interesting point. But would you need to know morse code to understand the message? Do you think the general population has been exposed to morse code enough to pick up the message subliminally?

There is a marketing technique in use called nueromarketing that works the way you are describing, using our senses. Sounds, smells, and colors are used in a way to get people to buy stuff.
 
Careyp74 said:
interesting point. But would you need to know morse code to understand the message? Do you think the general population has been exposed to morse code enough to pick up the message subliminally?
Click to expand...

Nope, you wouldn't. Morse only discovered the code, he didn't invent it. In actuality an innate knowledge and instinct to obey it was bred into the lower classes by the ancient Egyptians as a means of controlling large numbers of slaves via mirrors while building the pyramids. Learn something new every day, huh? :D
 
One of our profs has a near-IR sensitive video camera that we use in demonstrations all the time, and the remote control is a fun one. But "regular" (visual light) cameras are sensitive into the IR, too? I guess I figured they would have filtered for that before the light hit the CCD.... need to go experiment with this now!
 
jasonpatterson said:
Nope, you wouldn't. Morse only discovered the code, he didn't invent it. In actuality an innate knowledge and instinct to obey it was bred into the lower classes by the ancient Egyptians as a means of controlling large numbers of slaves via mirrors while building the pyramids. Learn something new every day, huh? :D
Click to expand...

I am going to turn into a conspiracy theorist if I read any more of your posts in this thread :)
 
NoisyAstronomer said:
One of our profs has a near-IR sensitive video camera that we use in demonstrations all the time, and the remote control is a fun one. But "regular" (visual light) cameras are sensitive into the IR, too? I guess I figured they would have filtered for that before the light hit the CCD.... need to go experiment with this now!
Click to expand...
Back in the analog film world, cameras loaded with infrared film would need a filter to remove (almost) everything BUT the IR light before it entered the camera, so the glass elements are passing at least some IR frequencies. I don't know what wavelengths standard CCDs are picking up; I should probably look into it.
 
Digital cameras are filtered to reduce their sensitivity to infrared, but the filtering isn't perfect. I'm relying on that for a camera I'm fitting into a birdbox, using near infrared LEDs for illumination.

Just for info, I tried 830nm and 880nm LEDs. The 830nm ones (being closer to visible wavelengths) also emit some red light while the 880nm ones produce almost none. Unfortunately either the camera I'm using is particularly insensitive to 880nm or maybe they're just not as bright, because they just don't illuminate the box well enough to see clearly. If I turn the current up they work a bit better, but then they emit almost as much red as the 830nm ones.

I think I need to experiment to find a red-absorbing reflector I can shine the LEDs onto so as not to freak out the birds when I switch on. In the dark, it looks like a cluster of little glowing red eyes :eek:
 
Jack by the hedge said:
I think I need to experiment to find a red-absorbing reflector I can shine the LEDs onto so as not to freak out the birds when I switch on. In the dark, it looks like a cluster of little glowing red eyes :eek:
Click to expand...

You could try a piece of lighting gel, Lee #120 would be the color you are after. It blocks most everything well into the IR. I can't find the page I ordered from, but it had the spectrum well into the IR and this didn't pass any visible red to speak of.
 
bokonon said:
Back in the analog film world, cameras loaded with infrared film would need a filter to remove (almost) everything BUT the IR light before it entered the camera, so the glass elements are passing at least some IR frequencies. I don't know what wavelengths standard CCDs are picking up; I should probably look into it.
Click to expand...


Back in the stone-aged days, better camera lenses had a special mark for infrared focussing, since the longer wavelength tended not to focus quite at the same place as visible light, even with lenses that were achromatic to visible light.

On this 50mm lens, it's that tiny dot indicated by the red arrow. If you were using infrared film with this lens, you'd focus through the camera, then look at this scale and move whatever distance is at the normal focus mark to the infrared mark.

50mm.jpg



On this 85mm to 210mm zoom lens, the difference between infrared and visible light focus depends on the focal length to which the lens is zoomed, so there are three marks given, corresponding to the shortest and longest focal lengths, and a middle focal length.

85mm-210mmZoom.jpg
 
Filter's a good idea - I'll see what I can find.

The different infrared focus position certainly rings true: at first I focused the camera at about 5" in visible light but then found in infrared it was completely defocused. (That was when I remembered about the offset IR focus position on my old SLR's lenses.) Refocusing at about 3" in visible light got it sharp at about 5" in IR.
 
Nestbox camera update: So, I got a nice 3" gelatin infrared filter from eBay (Kodak Wratten #87). It looks for all the world like a sheet of plain black plastic, but the TV remote works straight through it and, looking through a digital camera, sure enough the infrared LED on the remote is just as bright seen through the filter as without.

So much for the good news. My IR illumination shines straight through the filter, but unexpectedly, the visible red glow seems to go straight through too! But all other red light doesn't go through! :confused:

Took me a minute to figure out how stupid I was being: I think the red glow from the IR LEDs is not visible light at all - it's near infrared, which just happens to be so bright that it stimulates the red sensors in my eyes slightly. According to Wikipedia, birds seem to have the same colour vision we do, so there's nothing I can do to filter out the red glow. I guess I'll have to look at ways to diffuse it instead... :(
 
Ha! I had no idea you could see infrared light with a digital camera! I just tried it and sure enough it works.
 
You must log in or register to reply here.

Back
Top Bottom