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UltravioletPhotography

Photo Ninja: Colour Correction: Light Source Tab


Andrea B.

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EDITOR's NOTE: This was an old thread. I bumped it because it had a nice set of photos illustrating the Light Source choice that Bjørn and I debate from time-to-time. I'm hoping any one else who uses Photo Ninja can weigh in on what Light Source they use for their UV work. Bjørn and I have a debate about this from time-to-time. We switch sides too.

 

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In Photo Ninja I converted this Dicentra using a colour correction PreSet

made for my D600-broadband from the Labsphere Standards.

For this particular PreSet, Colour Temp = 2000 and Tint = -65.

(Sometimes the Tint can vary by a point or two, but my D600 is fairly stable around that Tint value.

 

The question then becomes:

what Light Source setting to choose from the drop down Light Source menu ??

I have these 4 choices: No Profile, Match Colour Temp, Daylight/Flash or D600_Visible.

This last one is a Visible profile I made with Photo Ninja's Colour Checker Passport Tool.

 

No Profile

This choice pushes the blue towards green.

600_6670ProofPnNoProfile.jpg

 

Match Colour Temp

This choice pushes the blue towards red. Too warm.

600_6670ProofPnMatchColTemp.jpg

 

Daylight/Flash

This choice also pushes the blue towards red. Too warm.

It is less saturated for some reason than the MCTemp just preceding. So too grey.

600_6670ProofPnDaylight.jpg

 

D600 Visible Profile

Its colour appears to be somewhere in between the colours of NoProf and MCTemp above.

Perhaps too saturated?

600_6670ProofPnD600Profile.jpg

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The logical choice would be for flash/daylight. The UV-capable flashes (uncoated xenon tube) have an output quite similar to sunshine and pretty much duplicate the actual spectral distribution of UV in sunlight.

 

The perception of "warm" etc. rendition has no direct bearing in the world of false colour. as long as the neutral objects (rocks here) are rendered neutral with no obvious cast.

 

My D3200 used in conjunction with SB-140 typically winds up with 2000 K and tint -57 or -58. With the Broncolor flashes the tint drops to -65 or thereabouts. The D600 ends up around 2000K and tint -74 with these flashes. So the sensors respond a little differently.

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Because we are blocking the red rays (of sunshine, of the SB-14, of the Brons) with our Baader-U, in my opinion, the logical choice is *not* Daylight. But darned if I know what *is* the logical choice !!

 

Every converter white balances these UV images slightly differently with slightly different temperatures. It's all somewhat maddening.

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I was thinking about UV here Andrea, not "red" as such.

 

This is a parallel to the discussion of crop factors. We leave out things (by the filter) but otherwise nothing is changed to the input.

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Yes.

I was speaking a bit figuratively. Apologies.

 

I was just trying to say that In my head I seem to associate UV with cooler false colours.

Of course, there is that pesky yellow to deal with !!

Hardly a cool colour, however yellow's luminance (luminosity/brightness, whatever)

makes it seem cooler than orange or red.

 

Actually I simply put this thread up to try to study up a bit more on our standardized UV false colour approach.

When I started with PN, it took me awhile to get a feel for all its settings.

I was surprised in some false colour fotos how different they could appear

when that Light Source tab is changed.

 

We seem to have settled on violet/blue and yellow as our false colour palette.

Occasionally some green shows up. I don't know if that green is valid or not.

(...a figurative use of "valid" there...)

Sometimes what I think is green is really a dark grey-yellow.

I am getting better at recognizing it.

 

There is name fog surrounding the colours I know as violet, purple and magenta.

Magenta for me is that saturated pinky colour which is a pure mix of R+B in light addition.

Purple is (1/2)R + B.

But, Violet - I have no idea how to represent. Maybe violet is just dark Purple?

 

If cyan shows up, I know I have either a light leak (some old fotos suffer from this)

or I don't quite have the WB correct.

I use the Color Correction Cyan slider to desaturate the cyan when trying to salvage a old foto.

 

Grey-blue also gives me difficulty. It tends to look purple to my eye.

 

The End of Colour Ramblings.

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The key difficulty: the same flower can legitimately have multiple false "blues"

in the blue/violet portion of our standardized palette.

Even if I make a choice of how to represent the blue, I cannot always achieve it reliably.

That somewhat trashes the idea of standardized colour.

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wikipee says that (approximately) Violet = (1/2)R + B and Purple = (1/2)R + (1/2)B.

 

So I have the names wrong I guess.

I will have to retrain myself to remember that Purple = Dark Magenta.

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  • 1 year later...

EDITOR's NOTE:

That was our first discussion about the Light Source choice.

Probably some of our thoughts presented above have changed.

We keep tryin' !!!

 

Does anyone who uses Photo Ninja besides Bjørn and me have any suggestions about the Light Source choice for UV photographs?

Discussion welcomed, as always.

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