Low IR reflective material

[Neil C Smith]

Hi all,

Wondered if anyone on the list might be able to help me with this. I'm looking for a material, ideally a fabric, that doesn't reflect much IR light - ie. will look close to black on the IR mode of a CCTV camera. Any ideas?

Thanks in advance,

Neil

Neil C Smith
Artist : Technologist : Adviser
http://neilcsmith.net

[AliT]

I'd have thought any matt deep black material will do the trick.

---

From: oxford-h...@googlegroups.com [mailto:oxford-h...@googlegroups.com] On Behalf Of Neil C Smith
Sent: 08 February 2013 20:30
To: oxford-h...@googlegroups.com
Subject: [Oxhack] Low IR reflective material

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[Neil C Smith]

Hi both,

Thanks for the input. Trying to respond in the right thread - hey,
Philip, how about switching off digest mode? :-) Really screws with
threading, and I missed one of your responses until this morning.

>> "AliT" <al...@talktalk.net> Feb 08 09:52PM

>>
>> I'd have thought any matt deep black material will do the trick.
>>

I assumed that too. Experience so far would appear to disprove that.

>> Philip Leichauer
>> Sent: 09 February 2013 04:01
>>
>> I've found things behave strangely under IR. A lot of black clothes came
>> out
>> light blue for example. Very dependant on wavelength though... What short
>> of
>> camera are you using or is this a mission impossible style break in
>> somewhere?

Using a number of these -
http://www.swann.com/s/products/view/?product=1428 Not for nefarious
purposes, though! :-) In fact, standing out in black would probably
be the worst possible break-in tactic. Projection on Bonn Square -
http://www.dancinoxford.co.uk/whats-on/2013/meeting-point

Like you, we've found a lot of things that are visibly black showing
up almost white (camera switches to monochrome output when on IR
mode).

>> "AliT" <al...@talktalk.net> Feb 10 01:21PM
>>
>> I'm using ink-jet printed paper to provide a colour-encoded surface for a
>> project I'm working on. I measure the reflection of an infra-red LED on
>> the
>> surface with a photo-transistor. From this I can tell you with certainty
>> that black and blue inks give minimal reflection to infra-red.
>>

Some of the reading I've done over the weekend would suggest this is
also partly to do with the fact that it's paper, which is meant to
have low IR reflectivity. Mind you, the camera is definitely seeing
reflection from white paper!

>> The trick will be to make sure you're really using black cloth. I've had
>> enough black clothes that have faded over time to grey, which is a colour
>> that does reflect IR. Also I suspect many supposedly black dyes aren't as
>> black as they say.

Cotton is also meant to have low IR reflectivity. I have two old 100%
cotton T-shirts, which are both quite grey looking now - one shows up
black, and one almost white. So, I guess you're right that the dyes
are the factor here.

>> Black velvet might be another approach, as it's non-smooth
>> surface will tend to disperse rather than reflect the light.
>>

Not tried velvet, but tried a matt black felt material and it was one
of the worst. Interestingly, reflective materials are quite
interesting, because as long as the reflection is slightly off from
the camera they show up dark - mirrors are great - but unfortunately,
putting a 2m square pane of glass in the middle of Bonn Square may not
be an option! :-)

Anyway, I've found two materials that do seem to do what we need - a
rough weave black cotton and weed control. As weed control is a lot
cheaper, we'll probably use that.

Thanks and best wishes,

Neil

--

Neil C Smith
Artist : Technologist : Adviser
http://neilcsmith.net

Praxis LIVE - open-source, graphical environment for rapid development
of intermedia performance tools, projections and interactive spaces -
http://code.google.com/p/praxis

OpenEye - specialist web solutions for the cultural, education,
charitable and local government sectors - http://openeye.info

[AliT]

Three thoughts.

1. The thing you're covering and the material are cold aren't they? Anything
warm will be very visible in the IR spectrum. Sorry for stating the obvious.
I'm sure you're already aware of this.
2. Your problem may be with the illuminating light source rather than the
camera. If it's radiating outside the IR part of the spectrum it could cause
weird things to happen.
3. Glad you seem to have found a suitable material but must ask, what on
earth is weed control? Thought it was what you did to a lawn, but you make
it sound like some kind of fabric??

Your project sounds very interesting. Not heard of the festival before. Will
have to 'boogie on down'...

-----Original Message-----
From: oxford-h...@googlegroups.com
[mailto:oxford-h...@googlegroups.com] On Behalf Of Neil C Smith

[Neil C Smith]

Hi,

On 11 February 2013 11:09, AliT <al...@talktalk.net> wrote:
> 1. The thing you're covering and the material are cold aren't they? Anything
> warm will be very visible in the IR spectrum. Sorry for stating the obvious.
> I'm sure you're already aware of this.
> 2. Your problem may be with the illuminating light source rather than the
> camera. If it's radiating outside the IR part of the spectrum it could cause
> weird things to happen.

The camera is the illumination source - it has 20 IR LEDs build into
it. We're not actually covering anything as such - the fabric will be
used as a hanging backdrop. However, my experience so far with
modified webcams and these CCTV cameras is that warmth (at least body
temperature warmth) is barely picked up if at all.

> 3. Glad you seem to have found a suitable material but must ask, what on
> earth is weed control? Thought it was what you did to a lawn, but you make
> it sound like some kind of fabric??
>

Yes, it's a type of plastic fabric - try googling "weed control
fabric" or "weed control membrane". I can't remember the exact
manufacturer of the one I've tried - will note it down when I buy some
more. Bin bags have a similar property - I think it may be that the
material is close to transparent to IR light. Do need to do some
testing to make sure things behind it are not being illuminated!

> Your project sounds very interesting. Not heard of the festival before. Will
> have to 'boogie on down'...

Great! See you there! :-)

Best wishes.

[Tim Stephens]

I'm coming in late here, but:

> On 11 February 2013 11:09, AliT <alit@> wrote:
> > 1. The thing you're covering and the material are cold aren't they? Anything
> > warm will be very visible in the IR spectrum. Sorry for stating the obvious.
> > I'm sure you're already aware of this.

CCD cameras are only sensitive to about 1100nm (which is where silicon becomes transparent). Heat from room temperature sources is about 10um or thereabouts, so there's no way that it's going to be picked up.

What's probably happening is that the blue filter on the sensor is transmitting some of the IR light, and the camera is then interpolating that to mean that it's looking at a blue subject.

I'd imagine that the illuminators are approximately 850nm, which is just outside the visible spectrum but where the camera still has some sensitivity.

As for what the best non-reflecting surface is, I'd suggest something that is matt-black or rough. You'll still get some specular reflection, but there's nothing that you can do about that.

Tim

On Mon, Feb 11, 2013 at 11:45:22AM +0000, Neil C Smith wrote:
> Hi,