fun with IR, UV and visible images of the same subject - stacking

[Fandyus]

I did this yesterday impulsively and it has been one of the most fun and rewarding projects I've done in a while. That's why I decided to share it with you today.

I took three total images of the same subject, from the same perspective, with different parts of the spectrum filtered.

The subject is a random plant my mother owns, a PTFE sheet, and my RGB LED strip controller. I wanted to use it as an improvised color checker, but it didn't work out so well since the actual dye containing layer is covered with UV- absorbing plastic from what I see.

 

(lightsource for each image was just sunlight) Here are the images:

visible

 

IR (720nm)

 

UV (ZWB2 + QB39) - this was shot with only the light coming through the window, it is winter so opening all the windows was not an option, but it seems to have produced an ok quality image regardless, only downside being that the exposure time needed was long, around three minutes.

 

 

The images at this point are perfectly aligned, you can download them and stack them yourself, they should fit perfectly. And it was a lot of work to align them I admit, photoshop failed at doing it properly so I had to do it fully manually. Worth it.

Prior to aligning, all the images were rendered using darktable, with light balance set on the PTFE sheet, most processing options turned off with the exception of highlight reconstruction in the UV image. That is why they are so flat, nothing should be blown out here. Upcoming images are more edited.

I used AMaZE + VNG4 as my demosaicing method.

 

In this next portion, I will showcase two trichromes I produced using this data and their color corrected variants.

 

IR-R  Visible-G  UV-B trichrome

 

As you can see, this image looks a little weird, I think it is because the illumination in UV was not the best, causing extreme contrast, though I'm not entirely sure if the yellow cast would go away if I brought the whole setup on open sunlight, maybe I am just unlucky and almost all the materials visualized absorb significantly more in UV, including my grey wall paint.

 

I took the liberty of color correcting the photo to bring out some color details.

Looks a bit less washed out, not perfect but sufficient.

 

Next I have a GBUV stack. I extracted the green and blue channels from the visible image, mapped them to red and green, then I mapped the UV channel to blue.

 

Once again, the image is washed out, so here's the color corrected version.

 

 

Up next I have a few things that might not be of more "scientific" significance, but I think they're really fun. For this I used the photoshop stack mode function for smart objects.

I used the maximum, minimum, median and mean functions.

https://helpx.adobe.com/photoshop/using/image-stacks.html

On this website, you can find a full list of possible stack modes that I could use plus their practical and mathematical explanation. I ended up not using entropy, kurtosis, range, skewness, standard deviation, summation and variance. If anyone would like to see these please do tell me so I can add them. They're mostly just a jumbled mess of seemingly random colors or completely white though.

Keep in mind I normalized and edited the images a bit, so for example the upcoming minimum isn't extremely dark. If you want to see the unedited versions, again please do tell.

 

stack mode minimum

 

stack mode maximum

 

stack mode mean

 

stack mode median

 

 

And the last series of images which I think are the most interesting. They are the IR and the UV images layered with the visible image in "color" mode. So that the image keeps the texture of the UV/IR image but the colors are normal.

 

IR

 

And my favorite, UV.

I think the UV really is an interesting aesthetic that could perhaps be used in product photography or something, I dunno, just find the image really interesting to look at.

That's all, I'm about to go watch a movie, I hope you liked my post, see you in the comments!

 

[Nate]

Those are some great images, I find that last one my favorite too, but the IR ones are close second. May or may not be your window issue, but I was planning on some window sill shots, and it turned out my window blocked so much of the UV.(double pane energy efficient)

Anyways, great work on the stacks.

[Andrea B.]

Good series showing some nice multispectral stacking varieties.

 

I particularly enjoyed seeing the min, max, mean and median modes. We don't see those here too often.

 

 

[Stefano]

I really like these stacks. They still look "natural" to me, despite being made using (also) invisible light.

[Cadmium]

Yes, I agree with Stefano. Nice group.

[colinbm]

Wow Fandyus these are all fantastic & very artistry too, you must of had a huge amount of fun doing these.

[Fandyus]

6 hours ago, Nate said:

Those are some great images, I find that last one my favorite too, but the IR ones are close second. May or may not be your window issue, but I was planning on some window sill shots, and it turned out my window blocked so much of the UV.(double pane energy efficient)

Anyways, great work on the stacks.

Thanks! I think my windows are that too, I don't know if double pane is the term but I know that the windows I have are also two panes with vacuum in-between to minimize heat transfer. They do shift the tone of UV into the violet a little bit when used with the ZWB2.

5 hours ago, Andrea B. said:

Good series showing some nice multispectral stacking varieties.

 

I particularly enjoyed seeing the min, max, mean and median modes. We don't see those here too often.

 

 

Thanks! I hope others do this too, I think the images are very fun to see.

[Fandyus]

5 hours ago, Stefano said:

I really like these stacks. They still look "natural" to me, despite being made using (also) invisible light.

Thanks! Do you mean any stacks in particular or just all of them?

2 hours ago, Cadmium said:

Yes, I agree with Stefano. Nice group.

Thanks, Cadmium.

[Fandyus]

23 minutes ago, colinbm said:

Wow Fandyus these are all fantastic & very artistry too, you must of had a huge amount of fun doing these.

Thanks a lot! Yes I have had a lot of fun for sure, the not so fun part was aligning the pictures though, the Industar 50-2 I use has a slight issue with focus breathing.

[dabateman]

You can try Bernard's Hugin alignment method to see if that works better. 

Outlined here:

https://www.ultravioletphotography.com/content/index.php?/topic/3536-composite-uv-imaging-using-multiple-filters/#comment-30723

 

 

The full process that Bernard used to do the same kind of thing was written here:

https://www.ultravioletphotography.com/content/index.php?/topic/3500-fullfalse-colour-uv-photography/#comment-30286

 

I like these as well. Its fun to switch the various wavelengths into the color channels.

Also good not to limit yourself to a standard blue channel always equals UV or red, as some images look better with a different mix.

 

I really like the stack mode minimum image with all the textures.  I will have to see if Affinity photo can so something similar.  I remember some of those settings there.

[Stefano]

11 hours ago, Fandyus said:

Thanks! Do you mean any stacks in particular or just all of them?

I mean all of them except the last four (minimum, maximum, mean and median).

[Guest]

I like that plant in burgundy.

[OlDoinyo]

So I understand the last two images are: luminance, IR or UV; hue and chrominance, visible. Am I correct?

[Fandyus]

21 hours ago, Stefano said:

I mean all of them except the last four (minimum, maximum, mean and median).

I see thanks.

20 hours ago, Blazer0ne said:

I like that plant in burgundy.

For sure, GBUV stacks are interesting and I think they should be explored more, with plants especially.

Thanks.

[Fandyus]

6 hours ago, OlDoinyo said:

So I understand the last two images are: luminance, IR or UV; hue and chrominance, visible. Am I correct?

Well I don't know the difference between hue and chrominance. Not sure what blend mode I used, it was either luminance on top of the visible image or color on top of the two IR and UV images.

[OlDoinyo]

Roughly speaking, hue is the tint of the color.

Chrominance is the intensity (saturation) of the color.

 

I was inspired by this to post some image mash-ups of my own. The subject is the Fiasco Farm barn in Ellisville. IL, which I mentioned in a previous post. Some of the source images are marred by an artifact, so are not exactly artistic-grade. But I had some fun anyway.

 

The last two images were constructed by switching to Lab color in Photoshop, which isolates the luminance channel of the image and enables paste-in from another image. The final image type might conceivably have some forensic or technical potential, but I am unsure about that point.

[colinbm]

Interesting collection, the UV luminance certainly holds the details.

[lukaszgryglicki]

Yes, also love the last two - very interesting.

[Fandyus]

Right! Anyhow, I'm most glad to have inspired you. These are some nice results you have. Intrestingly enough, the GBU stack looks like a normal full spectrum picture. Thanks for posting, maybe you should make this it's own post, actually.

[Doug A]

@Fandyus really neat images. The different variations are enlightening. You have shown there's so much we don't see. Fascinating.

 

Thanks for sharing,

Doug A

[Doug A]

@OlDoinyo your barn variations are very nice. Amazing what can be captured, with enough effort.

 

Thanks for sharing,

Doug A

[Fandyus]

On 12/15/2021 at 6:58 AM, Doug A said:

@Fandyus really neat images. The different variations are enlightening. You have shown there's so much we don't see. Fascinating.

 

Thanks for sharing,

Doug A

Thanks a lot for the compliment, Doug. Glad you like it.