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Multispectral backdrop test

Multispectral
17 replies to this topic

#1 Mark

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Posted 19 March 2017 - 04:15

I've been looking for a good backdrop for my multispectral image sets - ideally, one that will appear the same in each of the images (black). To this point the most problematic images have been the UV shots; which always yield a bright background. After trying a number of materials I figured I'd try something that is made specifically to absorb light... flock paper (https://www.edmundop...material/54582/). It appears very matte black, and in fact works very well, except in my UV images!

Here's a side by side of a few test subjects in my usual shooting setup, IR on the left, UV on the right:
Attached Image: 03-18-2017_21-05-25.jpg
(uncapped vials, left to right are: ammonia based window cleaner, ginger root extract, chlorophyll extract in IPA)

One thing to note here is that the only thing which seems to be consistently UV dark is the black porcelain plate I shoot my subjects on. But then that turns out to be IR bright! :blink:

I know distance can fix this problem, but then I would lose the controlled lighting setup I get from shooting in the box. I would try Acktar foil, but it is cost prohibitive for my application. Just sharing my experience here for anyone considering flock paper for such an application.

#2 Andy Perrin

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Posted 19 March 2017 - 04:22

What about actual velvet or felt? And didn't someone mention a UV dark paint last time this came up?

Edited by Andy Perrin, 19 March 2017 - 04:24.


#3 Mark

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Posted 19 March 2017 - 04:37

I tried UV dark paint; which wound up being IR bright. I've been hesitant to try felt, etc - but at this point it might just be worth the trip to the fabric store. Actually, if it works it will be well worth it. I'll give it a try.

#4 Hornblende

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Posted 19 March 2017 - 04:38

Could you use sunscreen?

#5 Andy Perrin

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Posted 19 March 2017 - 04:48

what if you took clear sunscreen and sprayed it on something visible and IR dark?

#6 Cadmium

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Posted 19 March 2017 - 05:52

I am using a black flock paper strip here in these tests, and mine stays black in UV
(specifically, I got mine from Edmund Scientific at the time, but I can't find it on that website now).
Your flock paper is reverse of mine, bright in UV and dark in IR, mine is bright in IR and dark in UV.
I have found black rubber stays black in UV, and in visual, and in IR. The black rubber sheet is not exactly clean, and has some reflection at certain angles, I suppose it could be sanded.
So perhaps there is some black rubber background that has a mat surface with less tendency to reflect light.
(I am not affiliated with WhiPur in any way. That was a joke).
Attached Image: UV_Visual_IR_850nm_Background_Material_Tests_1280.jpg

Edited by Cadmium, 19 March 2017 - 06:06.


#7 Mark

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Posted 19 March 2017 - 12:39

I did try SPF30 sunscreen - that was my very first attempt; which yielded flares/reflections (maybe I should have tried various sunscreens). I like the sanded black rubber idea. I'll try that too.

#8 Shane

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Posted 19 March 2017 - 15:50

Krylon 1602 ultra flat black paint. Must be purchased from an industrial supplier (in a spray can). Non UV-V-IR reflective and flat black.

Edited by Shane, 19 March 2017 - 15:56.


#9 Andy Perrin

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Posted 19 March 2017 - 16:00

View PostShane, on 19 March 2017 - 15:50, said:

Krylon 1602 ultra flat black paint. Must be purchased from an industrial supplier (in a spray can). Non UV-V-IR reflective and flat black.
Yes, this is the one I was thinking of above. (Have not tried it myself, but I think you mentioned it before somewhere.)

#10 Cadmium

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Posted 19 March 2017 - 16:52

Black plastic, maybe ABS or some other type, might stay black in UV and IR, take your camera to some plastic place maybe.
Some kind of plastic sheet might be more applicable because it stays rigid.

#11 Shane

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Posted 19 March 2017 - 17:28

Tested a lot of plastics years ago, never found any except Spectralon black. However, I did spray plastic sheet with the Krylon suggested above - worked beautifully for custom built spectroscopy application too.

Edited by Shane, 19 March 2017 - 17:28.


#12 Mark

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Posted 19 March 2017 - 18:49

I did try a Krylon matte black paint once; but it was just some type available at the local hardware store (not the 1602), and it didn't work. I'm just about to test a few different fabrics I picked up today. If none of these work then I'll see if I can order some of the 1602 online somewhere.

#13 Shane

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Posted 19 March 2017 - 18:56

I tested many black paints and you are correct the "regular" Krylons blacks do not work well. Last I looked you order a 6 pack of aerosols for something like $30

#14 Mark

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Posted 19 March 2017 - 21:08

I just compared four different fabrics as potential backdrop options: 100% nylon, 90% PVC (10% "poly"), black felt (plush), and black felt (matte). Unfortunately, none stayed dark across UV-VIS-IR. What's more is I don't even think the two felt options I picked up were actually made of the same material, as one of them (plush) fluoresced red rather strongly in the UVIVF image!

Interestingly, the flock paper I recent got showed inverse absorption under UV vs IR on the front vs back side of the paper (I wouldn't have even considered using the back side of the paper otherwise).

Illumination(s):
  • VIS: flash; IR: 40W clear glass incandescent bulb; UVIVF & UV: 4x18" T8BLB
Attached Image: 03-19-2017_14-44-31.jpg
(all images were desaturated for easy comparison, except the UVIVF image)

A couple things to note here as well. First, my go-to filter stack for my UVIVF images works very well - as evidenced by the virtual absence of any reflection of the light source (on the porcelain plate/shooting surface). I'm happy to see that. Second, its probably a bad idea to use fabric as a backdrop anyway - given how much lint it attracts! And its not easy to clean/remove lint from these textured fabrics.

I think its time I move on to an open setup, where the background is out of illumination range. I think this will work out well, except for the UVIVF images. I'll need to figure out some way of preventing off-target fluorescence (in the surrounding room) from contaminating the image.

Good thing I like challenges :)

#15 Shane

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Posted 19 March 2017 - 21:14

I'm not saying to stop looking, however 10 years ago I did extensive testing of plastics, fabrics, paints and other materials to be used as a backdrop for UV, IR and fluorescence photography, the only one that worked (for minimal cost) was the above mentioned Krylon.

#16 Andy Perrin

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Posted 19 March 2017 - 21:29

My only remaining suggestion is dark chocolate. LOTS of it. It won't change your reflectivity but it will make you feel better about the situation while you wait for the Krylon to arrive.

#17 Mark

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Posted 19 March 2017 - 23:58

Chocolate it is then!

#18 Cadmium

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Posted 20 March 2017 - 08:06

Thanks for that paint idea. I actually have a can of that same paint in my shop that I had for something once.
I was mistaken, I have some flat black, but not the Krylon 1602 ultra flat black paint.
If that is the blackest thing, then that would be great.

Edited by Cadmium, 20 March 2017 - 23:36.