A couple of references to papers with false color floral photos

[Andrea B.]

Like it, or not, flowers are one of the most fascinating and varied subjects that we can photograph in UV. The following papers were of interest to me recently because of their photographs of floral UV-signatures. I did not read these papers with any intent to prove or disprove their methods or conclusions. I was simply interested in what gear they used and how they made multispectral stacks. Also, I was interested in the particular flowers they photographed or analyzed.

 

 

A bee’s eye view of remarkable floral colour patterns in the south-west Australian biodiversity hotspot revealed by false colour photography

Klaus Lunau,  Daniela Scaccabarozzi,  Larissa Willing,  Kingsley Dixon

Annals of Botany, Volume 128, Issue 7, 9 November 2021, Pages 821–824, https://doi.org/10.1093/aob/mcab088

Published: 03 July 2021

 

LINKIE

Do go look at the photos. Also, lots of interesting info about UV-signatures, pollination, etc. I've really enjoyed this paper.

 

Here is the gear these folks used:

• full-spectrum Panasonic GH-1
• Ultra-Achromatic-Takumar 85/4.5
• Baader UV/IR-Cut, BaaderU
• white Teflon disc

 

(Hey, you saw it here first...... . Birna was using that GH-1 ten or more years ago with a UV-Nikkor.)

 

They made a UV and a Vis photo of the flower. The files were split into R, G, B channels. The stack was made using ImageJ like this:

• UV blue channel --> blue
• Vis blue channel --> green
• Vis green channel --> red

 

(Hey, you saw it here first......  But none of us got a published paper from our multispectral stacking efforts. Oh well. )

 

 

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This paper only has a couple of photos, but is still interesting.

 

Flower Colours through the Lens: Quantitative Measurement with Visible and Ultraviolet Digital Photography

Jair E. Garcia, Andrew D. Greentree, Mani Shrestha, Alan Dorin, Adrian G. Dyer

Published: May 14, 2014

https://doi.org/10.1371/journal.pone.0096646

 

These folks used a Canon D40 + Canon 100mm EF for Vis, Fuji S3 UVIR + UV-Nikkor 105/4.5 + BaaderU for UV, Nikon Speedlight SB-14 (modified by our member Shane Elen), a white reflectance standard, Color Checker Passport, grey barium sulphate target.

 

This is a complex paper with some serious spectrometric analysis. The authors wanted to use the linear response from the cameras so math ensues. But I was wondering if the linear data couldn't be extracted with Raw Digger? Or just Dcraw from the command line.

 

Some EXCELLENT points are made about camera response and human vision. (Example: "Camera responses are not radiometrically faithful for" "highly saturated, human-perceived yellow and orange colours" of Gazania rigens and Sonchus oleraceus. I note that this seems to also be valid for human-perceived violet and violet-blue colours.)

 

 

 

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cool website: http://www.jolyon.co.uk

 

Garden Flowers in Bee Vision

http://www.jolyon.co.uk/2020/07/garden-flowers-in-bee-vision/

Beautiful photos. ((Although you already know my comment about using reds and magentas for bee vision. ))

 

AND FREE, OPEN-SOURCE SOFTWARE !! Must look into this.

http://www.jolyon.co.uk/2019/04/a-new-home-for-the-micatoolbox-empiricalimaging-com/

• Excerpts from table of contents:
• How to Make Your Own Camera Calibration
• How to Make Your Own Colour & Grey Standard
• Creating a Calibrated Mspec Image

 

 

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False-colour photography: a novel digital approach to visualize the bee view of flowers

 

Christian VerhoevenHeinrich-Heine-University Duesseldorf

Zong-Xin RenChinese Academy of Sciences, Kunming

Klaus LunauHeinrich-Heine-University Duesseldorf

DOI: 

https://doi.org/10.26786/1920-7603(2018)11

2018

 

LINKIE

https://pollinationecology.org/index.php/jpe/article/view/482

Do look at the photos. They are quite nice whether or not you agree/disagree with the methodology.

 

Full-spectrum Panasonic GH-1 + Ultra-Achromatic-Takumar 85/4.5, white Teflon, grey spectralon, Baader UV/IR-Cut,  Nikon D40 camera with low-pass filter, 18-55 mm Nikkor lens and a 105 mm UV-Nikkor lens.

(Details not fully supplied on all gear or how it was used. Was that 18-55 used for UV?? Later there is made mention of an inexpensive "plastic lens" used for UV photos, so maybe it was that old 18-55?)

The UV-pass filter, the blue-pass filter and the green-pass filter are not specified. Why?

 

Three photos were made:  UV, visible under blue filter, visible under green filter.

The files were channel split. Then a multispectral stack was constructed:

• Green Filter Green Channel --> Red
• Blue Filter Blue Channel --> Green
• UV Red Channel --> Blue

 

[[Or perhaps we should tell them just to use a Bug filter ???  Sorry, I just couldn't resist. ]]

[Andrea B.]

This is an excerpt from the previously listed paper (which I fully attributed and linked). It has a bit of history of UV photography for "bee vision".

 

(Just a side note: It amazes me that none of these papers seem to know about photographers who experimented with UV photography of flowers, multispectral stacking and so forth. The people who taught me were Birna Rørslett, Klaus Schmidt, and Vivek Iyer. They were doing all of this long before this particular paper was written. Me too.)

 

 

EXCERPT highlighting some history of UV-photography used for "bee vision":

However, classical UV-photography using a UV-sensitive camera mounted on a tripod, UV-transmitting filter and UV-transmitting lens and a UV-sensitive film were still preferred to produce UV-photos with high quality (Biedinger & Barthlott 1993; Burr & Barthlott 1993; Burr et al. 1995; Lunau 2000). With the turn of the millennium,digital cameras were used mostly after having their internal UV-and IR-blocking filter removed and sometimes with the support ofa UV-lamp for illumination (Koski & Ashman 2013).

 

Several attempts have been made to develop methods to create colour pictures in bee view. As early as in 1958 Daumer tried to evaluate floral colours considering the bees’ colour perception. He took photographs with a yellow, a blue and a UV filter and calculated the “bee-colour” (Daumer 1958), but of course he did not have the option to merge the photographs to a bee view-picture. Vorobyev et al. (1997) developed a method based on video recordings of flowers made by a UV-sensitive camera and specially selected set of filters to reconstruct images of flowers as bees might see them by calculating the quantum catches of the honeybee photoreceptors for each ommatidium dependent on the distance between bee and flower.

 

Multispectral images, a series of black-and-white photos taken through different bandpass filters (Kevan 1972; Chittka and Kevan 2005) from alpine flowers of the Rocky Mountains, Colorado, are available from the Floral Image Database (http://liu.edu/flower). Benitez-Vieyra et al. (2007),Williams & Dyer (2007), Brito et al. (2015) and Hempel de Ibarra et al. (2015) presented false colour photos of flowers in bee view, some of which require sophisticated calculations or calibrations. Photographic methods have also been used for simultaneous quantitative measurements of spatial and spectral components of floral colour patterns as seen by bees (Vorobyev et al. 1997; Benitez-Vieyra et al. 2007; Williams & Dyer 2007; Hempel de Ibarra &Vorobyev 2009; Garcia et al. 2014; Hempel de Ibarra et al. 2015; White et al. 2015)

 

Recent studies presenting multispectral images from flowers in bee view (Garcia et al. 2014; Brito et al. 2015; Hempel de Ibarra et al. 2015; White et al. 2015; Vasas et al. 2017) are mostly focusing on one or few target species and /or require sophisticated calculations or calibrations.

 

In this study we introduce a simple and cheap method for general use based on a slightly modified and supplemented standard camera equipment to create UV-pictures and false-colour pictures in bee view and to highlight the rationale of this method for field studies. The estimated prices for a low-cost and a standard equipment as used in this study are shown in Supplement S1. This equipment is much less expensive than custom-built multispectral cameras, e.g. Spectrocam Multispectral Wheel Cameras (Ocean Optics). The pictures are intended to demonstrate the bee-subjective colour patterns of flowers in bee view with details that cannot be measured using a normal spectrophotometer. Moreover, it is demonstrated how false-colour pictures in bee view are used to better understand the impact of the bees’ sensitivity for ultraviolet and insensitivity for red light. For this purpose, false-colour pictures of floral colour changes and small-sized floral structures are shown as false-colour pictures. In addition, yet undescribed forms of colour patterns are described using false colour pictures such as blue bull’s eyes rather than ultraviolet bull’s eyes (Silberglied 1979; Koski & Ashman 2014). The robustness of this method is tested by the comparison of false-colour pictures taken with different cameras, lenses, filters, different picture editing programs and in field conditions.

 

 

[Andrew Dayer]

There does seem to be an insularity in the groups publishing papers and each 'discovering' UV imaging. I guess folks are pretty deep in their area of specialism before stumbling on some marginal and obscure reference to UV imaging and grabbing that for their field. Maybe they just didn't think to do a Google search for 'UV imaging'... Maybe some are just pushing out papers in volume [too cynical?].

 

Thanks for flagging these - some are surely new to me.

 

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http://www.jolyon.co.uk but now replaced by www.empiricalimaging.com. This is the same folks / software as discussed here: https://www.ultravioletphotography.com/content/index.php?/topic/3582-see-like-a-bee-free-download-lets-us-look-through-animal-eyes and other threads. Its a plugin to ImageJ that does seem to offer a sensible approach although I'm still trying to work out / validate the calibration steps, and work round some script errors (or maybe my installation's adrift).

 

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This one might be worth a look also:

 

"How to measure flower ultraviolet reflectance using digital photography" (2022) Francesca Napoleone, Davide Manzini, Sabina Burrascano https://onlinelibrary.wiley.com/doi/epdf/10.1111/avsc.12648

This line from Section 2.1 caught my eye: "The camera was equipped with a MC 28 mm f/2.8 macro lens (Sigma) which was selected for its transmittance at 365 nm and had no anti-reflective coatings or cement between the elements which may absorb UV and diminish the sensitivity range of the camera."

 

I presuming that this is the Sigma Mini-wide 28mm f2.8 multi-coated ("MC") AF lens but its not clear if that's the Mk I or Mk II version. The UV LED source isn't named either. Is it / are they actually any use for UV work?

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Verhoeven etal 2018. Rather confusing at times (translation issue, maybe?). "Nikon 18-55" / "plastic lens Nikon AF-S DX NIKKOR 18-55 mm" is presumably the kit lens available I believe with the Nikon D40X. I have a variant of this an it is a good DX travelling zoom. Plastic body but glass lenses. Very limited UV transmission. I'll read the whole paper later....

[Andrea B.]

Andrew writes: There does seem to be an insularity in the groups publishing papers and each 'discovering' UV imaging. I guess folks are pretty deep in their area of specialism before stumbling on some marginal and obscure reference to UV imaging and grabbing that for their field. Maybe they just didn't think to do a Google search for 'UV imaging'.

 

I was telling my SigOth about these papers which seem to know nothing about the contributions of UV photographers and he made the same comment about Google searching -- "don't they know they have to make a Google search these days in addition to a literature search?" Your comment about the insularity within certain research groups also rings true. 

 

To be fair (!), there are such a myriad of ways to make multispectral stacks, that a write-up about one those ways is probably useful for some other botanist/scientists. And they do acknowledge that multispectral stacking has been tried before.

 

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....Duck Duck Go search ok too. 

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I downloaded the Empirical Imaging software. But haven't had a chance yet to try it out. I'll report on that at some point. Regarding your [i.e., Andrew in preceding post] comment about script errors - is there a way to contact the EI folks? When I was on their website, I wanted to provide an answer to one of the questions on the forum. But I could not find any email addresses there. And my attempt to register failed. 

 

 

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Andrew writes:  The UV LED source isn't named either. Is it / are they actually any use for UV work?

 

I use a UV-LED flashlight primarily as a focusing aid* or for UV-induced fluorescence photos. With care, UV-LEDs can be used to make reflected UV photographs, preferably inside in the studio. Torchlight is rather concentrated and can make for hot areas in the photo. So I've always thought UV torches were best applied in light-painting mode over a few seconds exposure. It takes lots of practice and you cannot see the light you are painting with! I never thought I was very good with UV-LED light painting. Also, the narrowband 365nm UV-LED torches when used outdoors (on close subjects) had a different false colour outcome than what you would get from sunlight. So the photos made that way had discordant background versus subject colors, whether white balanced or not. Sometimes I would get that effect in UV-LED studio photos also, depending on what the ambient light was. But that is my experience. If you have a filter and lens which can "match" the peak wavelength of your UV-LED flashlight, then give it a try. And let us know what worked, and what didn't! "-)

 

* I think UV-LEDs are mandatory to own to use as a focusing aid for reflected UV work at close range.

 

[Andrew Dayer]

16 hours ago, Andrew Dayer said:

I'm presuming that this is the Sigma Mini-wide 28mm f2.8 multi-coated ("MC") AF lens but its not clear if that's the Mk I or Mk II version. The UV LED source isn't named either. Is it / are they actually any use for UV work?

Sorry Andrea. This was a badly composed paragraph as happens when doing n too many things at once. So I've caused you to unnecessarily write a none-the-less interesting and useful section on LED's.

 

I meant to say:

 

Point 1: seems like the paper means the Sigma Mini-wide 28mm f2.8 multi-coated ("MC") AF lens but its not clear if that's the Mk I or Mk II version. Is it / are they actually any use for UV work? ie anyone tried them?

 

Point 2: the paper mentions (and shows an image of) a large LED UV source but gives not more details.

 

You comments about narrow band LED's giving different false colours to sunlight is interesting and something I'd noticed but put down to my poor technique. I suppose that from a photography view point, a narrow beam torch is a pretty poor light source (point source, very directional even if mitigated somewhat by light painting) v's the photographically generally preferred large source with good diffusion. Sunny v's cloudy day... Of course, there's the very narrow band of wavelengths emitted by the torch as well. I suppose the reflected light is correspondingly narrow band and so gives a relatively stronger, clearer signal to the camera sensor?

 

UV diffusion, btw, is something I've got on my list once I've got beyond first base with spectrometry.

 

I noticed a similar effect with UVIVF (project last year). The colours were richer and more defined with the LED torch than with a modified flash. At the time, I put that down to visible light leakage past the 4mm of ZWB3 on the flash (which certainly was a problem at first) but now I think it was due to the wider and different (shorter) wavelengths the flash emitted.

 

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Empirical Imaging - not sure if they are very active. I guess careers and lives move on so focus on old projects limited. That said they are holding a workshop in September in Australia. It's a lot of airfare for one day...

 

I have posted a comment / query but as a first post (you have to submit a post before you get to login) it requires moderation and that hasn't happened yet, apparently. I do wonder that I've found script errors in relatively old software in the public domain - more likely I'm doing something wrong .

[Andrea B.]

No prob, Andrew.

 

Just guessing here, but "multi-coated" does not seem indicative of a good UV transmitting lens. But many lenses can capture something in the 380-400 nm range.

 

Andrew writes: I noticed a similar effect with UVIVF (project last year). The colours were richer and more defined with the LED torch than with a modified flash.

Exposure time plays a big role in fluorescence photography. Some fluorescence is very low. So to really see it in a photo, a longer exposure is needed. The UV-LED torch can provide that. The UV-flash may not.

 

I think a lot of fluor photos are over-exposed though. The longer the exposure, the more reflected light you are capturing rather than just the fluorescent light. It's tricky!! And artistry can play a role.

 

For documentary fluorescence, use of standards is necessary to indicate the strength of the fluorescence.

 

When you make a UV-induced fluor photo with a UV-flash, it is fair, given the shorter exposure time, to boost the exposure in post to bring up the fluor to the level you were actually observing.