• Ultraviolet Photography

Experiment: does drying a coneflower change its SWIR pattern?

Infrared SWIR Processing
4 replies to this topic

#1 Andy Perrin


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Posted 15 July 2019 - 08:48

I took a photo of a coneflower several days ago, and people were curious about what would happen if I repeated the photos with the dried flower, because water strongly absorbs SWIR light, so the pattern may simply reflect the water distribution in the flower.

The flower was picked on July 12, at 12am and imaged immediately after picking. Because this was not a planned experiment, I did not write down all the exact photographic settings that I used in this image set, so the followup may have slightly different contrast. I don't think it will matter for the purpose, since we are not trying to extract quantitative information. The flower was reimaged just now (July 15, 3am), 75 hours later.

In order to make a valid comparison, I think I need to show how the images look straight out of camera, with no processing, in both sets. Then I will show the processed results.

This is SOC, except for resizing and labeling.
Attached Image: coneflower comparison, SOC.jpg

After subtracting off the pattern noise of the sensor, here are the results:
Attached Image: coneflower comparison, depatterned.jpg

And with sharpening and local contrast adjustment:
Attached Image: coneflower comparison, depatterned+sharp.jpg

There is clearly no significant change in "SWIR signature" of this flower after it is thoroughly dried.

#2 dabateman

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Posted 15 July 2019 - 12:37

Very cool.
Do you have any powdered sugar?
I now think the darkness is sugar groups, like the darkness I see in deeper UV.
If you have some, sprinkle it on something to see if it darkens up the object.
Or even the petals of this dry flower.
Brown or regular white sugar should work as well, just the crystals may reflect light.

Edited by dabateman, 15 July 2019 - 13:01.

#3 Andy Perrin


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Posted 15 July 2019 - 16:35

Oh, I already did those experiments back here:

Sugar is definitely quite dark.

#4 Andrea B.

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Posted 17 July 2019 - 21:12

Andy, I was thinking that this might be a very interesting experiment to make with autumn leaves. When the leaves begin to turn color and drop off the tree, you can usually find some still green along with some which have changed color and dropped. Of the dropped ones, some are still have moisture content and some are much drier. All kinds of comparative possibilities to explore!!

And I'm eager to see what Pokeberries look like in SWIR.
For newer readers, we've had some great Pokeberry photos - especially in IR.
Andrea G. Blum
Often found hanging out with flowers & bees.

#5 Andy Perrin


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Posted 17 July 2019 - 22:55

My guess is that Pokeberries will be dark in 1500-1600nm SWIR because of the moisture. So far it seems that flowers don’t have enough moisture to matter but leaf veins (or whatever you call the main pipes that branch out) do.

What I really want is a filter wheel so I can do color SWIR pics. I want to do something like 1300-1400nm, 1400-1500nm, 1500-1600nm in RGB (or BGR).

Edited by Andy Perrin, 17 July 2019 - 23:08.