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Gourd 2020

Fluorescence White Balance
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#1 Andy Perrin

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Posted 21 November 2020 - 08:20

Once again I am attempting UVIVF on a gourd. Long-time followers of this forum will remember my cursed (but gorgeous) first attempt. This time I have taken a great deal more care with the color processing. Whether it was worth it, I leave up to you all to decide.

The new procedure was as follows.

Equipment
Nemo torch with fluorescent ring placed behind the filter to prevent contamination. Filter is the stock filter that came with it.
Color Checker Passport 2019
Micro-Nikkor 55mm/2.8 lens
Sony A7S camera (converted)
Aluminum foil
Foldio light box for diffuse lighting

Stack
BG38 2mm + Tiffen Haze 2E

Process
I placed the Color Checker inside the Foldio box with the built-in white LED lights on and took a photo of it. I followed Andrea's directions for producing a Custom Light Profile in PhotoNinja, using white balance off the white square in the Color Checker. The resulting image of the Color Checker after the Custom Profile was applied looked like this:
Attached Image: _DSC0002 Color checker.jpg

I then placed the gourd on a piece of aluminum foil (dull side up) and shot a lot of photos of it under the same lighting as I used above with the Color Checker but with focus varied in small increments. (This was done using the Sony Imaging Edge software to take photos directly into the computer as I changed the focus.) I used Photoshop CS6 to make a focal stack and produced the following image. The image has been adjusted for contrast and to white out the aluminum foil:

Attached Image: Gourd visible focal stack UVP.jpg

I then removed the Foldio box (which fluoresces brightly) and placed the gourd back on the foil and turned out the lights. I shined the Nemo torch on it using several 1" ISO100 F/8 exposures to make another focal stack. The image below was the result, with some further adjustments in Photoshop to remove lint in the background, and also to tweak contrast. I didn't change the colors this time, having gone to so much trouble to get them. I fully realize that using the white balance of the Foldio lights for this is just as arbitrary as ANY OTHER CHOICE of UVIVF white balance (with the possible exception of those expensive UVIVF white balance standards that Andrea has).

Attached Image: Gourd UVIVF PN UVP.jpg

#2 colinbm

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Posted 21 November 2020 - 10:17

This is good thanks Andy
You have been very methodical & followed a procedure that you have documented.
Is this essentially how you saw it with your own eyes ?

#3 Andy Perrin

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Posted 21 November 2020 - 15:57

Colin- similar, but it’s actually irrelevant how I saw it. I’m partially colorblind so it wouldn’t match how anyone else saw it anyway.

#4 Stefano

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Posted 21 November 2020 - 16:02

Andy, I was actually thinking about your colorblindness when Colin asked the question, and if you think about it, it doesn't matter. You see both the real gourd and the image you posted in the same "wrong" way, so if they match for you they will match for everyone.

#5 colinbm

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Posted 21 November 2020 - 16:25

View PostAndy Perrin, on 21 November 2020 - 15:57, said:

Colin- similar, but it’s actually irrelevant how I saw it. I’m partially colorblind so it wouldn’t match how anyone else saw it anyway.

Thanks Andy & sorry for my ignorance :unsure:
That explains why you have taken so much care with your processing.

#6 Andy Perrin

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Posted 21 November 2020 - 16:56

Stefano, kind of you but colorblindness doesn’t work that way. Colorblindness is basically having many more metamers than people with normal vision, so for example certain shades of pink and light green look identical to me while they would not to you. It’s not just a remapping of the colors.

That said, my vision works pretty well on the blue-green end where I THINK this gourd fluorescence is, so it probably is a good match.

Edited by Andy Perrin, 21 November 2020 - 17:00.


#7 Stefano

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Posted 21 November 2020 - 17:55

Thanks Andy. I looked a bit on Wikipedia, and there are a lot of types of colorblindness. I knew three (four with achromatopsia), but there are actually more, some are very rare, some are quite commom. What type do you have?

In your UVIVF image, the gourd does appear blue-green to me. I got tested for colorblindness some time ago during a general vision check, and I can see the numbers on the Ishihara plates, so my vision is normal. I see mainly a bluish-green background with cyan stripes, and some bumps are slightly red.

#8 Andy Perrin

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Posted 21 November 2020 - 17:57

I told you already - red/green! I don't recall the technical name for it, but it's the most common. I have a friend who was injured in some kind of accident with a laser and she has the blue/yellow variety which is REALLY rare.

#9 dabateman

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Posted 21 November 2020 - 20:44

Great image.
I don't think its a bad idea to show the world artistically what you see.
Might be great for images. We have been trying to make trees, purple (chocolate filter), orange (B410), red (729+k3), white (Lp830nm). Why not color something fun.

#10 Stefano

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Posted 21 November 2020 - 21:54

We can make trees all colors. Even green, don't forget.

Sometimes our images remind me of Andy Warhol's Marilyn Monroe pop art.