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Lumix GH1 Broadband: White Balance & Colour Correction in Photo Ninja [& Midtone Curve Discussion]


Andrea B.

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EDITOR'S NOTE: I changed the title of this post to make it more accurate.

FORMER TITLE: Lumix GH1 Standards Shoot & Photo Ninja Edit [Midtone Curve Discussion]

NEW TITLE: Lumix GH1Broadband: Visible Colour Correction in Photo Ninja [& Midtone Curve Discussion]

 

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I was diligent enough in 2011 to actually put together a nice little box of Standards, Flowers and Mini CC Passport and shoot it with my Panasonic Lumix GH1 using a few different filters in order to make some presets for that camera.

 

I thought it might be useful(?) for you to see such a test setup as well as to note the interesting differences between the 3 UV-pass filters after being white-balanced in Photo Ninja. Those UV-pass filters were: Baader-U, the test version of the Andrea-U and an Omegabob 340AF15 from Ebay. I also included an unfiltered shot, a visible shot and an IR shot made with the B+W 092 IR-pass filter.

 

BTW, yes, of course, I do know my GH1 can actually obtain a reasonably good in-camera white balance. But colours must still be adjusted for accuracy, so presets are still needed. (Imho, however Ymmv, as always.) There may be other adjustment issues, as you will see in the 2nd post.

 

The box includes:

Top: Labsphere Spectralon® standards, Bidens ferulifolia and Rudbeckia hirta.

Bottom Left: Teflon® disk and B+W 093 IR-pass filter.

Bottom Right: XRite Color Checker Mini (since discontinued).

 

The two flowers were chosen as 'classic' UV-bullseye flowers. The B+W 093 IR-pass filter was included in the box to look for IR leakage. This particular filter at 830nm has no visible red leakage.

 

Edits:

In Photo Ninja I first white-balanced by dragging the Color Correction dropper one or more of the white standards. Then I made minor adjustments in exposure/highlights as needed. The Detail slider was applied at +10. I opened up the dark areas just a tiny bit with the Shadows slider because the GH1 has limited dynamic range. The Neutral (or 'Plain') colour setting was chosen.

 

Equipment [Panasonic Lumix GH1-broadband + some UV-Pass Lens]

My apology for not remembering which lens I was using.

 

Unfiltered [f/4 for 1/1600" @ ISO 100 in Sunlight with no filtration]

Look at the 092 filter to see that IR light is hitting the sensor in an unfiltered, broadband camera. No surprise, of course. Then compare this shot to the next Visible shot to see the damage that IR light does to the colours.

standardsGH1_IncUnfiltered_081311wf_orig13pn.jpg

 

Visible Light [f/4 for 1/1000" @ ISO 100 in Sunlight with Baader UVIR-Block Filter]

standardsGH1_IncBaaderUVIRCut_081311wf_orig14pn1.jpg

 

Infrared Light [f/4 for 1/640" @ ISO 100 in Sunlight with B+W 092 IR-Pass Filter]

The GH1 produces such a pretty blue for the 092 after white balancing.

On back of the 093 filter you can see the scotch tape which unrolled in the heat.

I was using it on the 093 filter rim to try to keep the it from falling out of the box.

standardsGH1_Inc092IR_081311wf_orig18pn.jpg

 

Ultraviolet Light [f/4 for 1/8" @ ISO 100 in Sunlight with Baader UV-Pass Filter]

standardsGH1_IncBaaderU_081311wf_orig15pn.jpg

 

Ultraviolet Light [f/4 for 1/10" @ ISO 100 in Sunlight with Andrea-U UV-Pass Filter]

Please remember that this was a test version of the Andrea-U.

I think there might have been some changes to the filter since I first tested it.

The Andrea-U gives bluer blues after white balancing.

standardsGH1_IncAndreaU_081311wf_orig16pn.jpg

 

Ultraviolet Light [f/4 for 1.6" @ ISO 100 in Sunlight with 340AF15 UV-Pass Filter]

This is a very small diameter filter. Try to disregard the peripheral discolorations due to that.

I really don't know if the greenish colour is supposed to be there or not.

standardsGH1_Inc340U_081311wf_orig17pn.jpg

 

Added --

Ultraviolet Light [preceding photo as originally shot, before white balancing]

The 340AF15 UV-pass filter is very narrowband, so it produces an almost monochrome frame

which gives an almost B&W appearance after white-balancing in the editor.

I used the 'Halogen' in-camera white balancing setting when shooting this original.

standardsGH1_Inc340U_081311wf_orig17.jpg

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OK, now let's look again at the Visible shot.

 

If I measure the Brightness (using the HSB model) of the those top 4 Spectralon® reflective standards using a 5-pixel Photoshop dropper, I get approximate Brightness readings (as marked on the photo) of 93, 85, 75 and 9%. The actual reflectivity of those 4 standards is 99, 75, 50 and 2%.

 

[side Note: We can debate at another time just how well diffuse reflectivity translates to Brightness in the HSB model, but really these colour models like HSB, Lab, etc. are all we have to work with when editing photos.]

 

So with this photo you can see what happens to raw data with application of a gamma curve during conversion. The midtones are lifted a lot to mimic the way our eyes see the world. Remember that lots of other tweaks are applied during conversion so this is not an exact experiment by any means.

 

Granted I did perform some minor edits to the photo - to make the best out of it as I could. The shadows lift I did probably messed up the black standard's value. But I did no edits so drastic as to lift a 50% reflectivity to a corresponding 75% brightness - that is strictly from the application of a midtone lift during conversion.

Jamming the photo into a postable Jpeg probably does not help matters, but I don't think it harms the neutral colours all that much.

 

Photo: 93,85,75,9

Standards: 99,75,50,2

standardsGH1_IncBaaderUVIRCut_081311wf_orig14pn101text.jpg

 

 

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Here is the same photo with the white and black points reset on the 99% white and 2% black standards using the PS Level tool's black & white droppers themselves set to 99/2% brightness. You can see that the two middle standards are even brighter now.

[side Note: Setting black & white points can potentially 'stretch' the histogram in some photos and produce banding or other artifacts. But this photo's initial histogram was spread out enough already so the minor tweak with the Level tool droppers doesn't harm it.]

 

Old: 93,85,75,9

New: 99,91,78,2

Ideal: 99,75,50,2

standardsGH1_IncBaaderUVIRCut_081311wf_orig14pn101wb.jpg

 

 

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Now, let me continue with this effort to equate Brightness with the reflectivity of the standards. This time I tried to lower the midtones while trying to keep the white and black as they are at 99/2%. I got close, but you can see immediately that the colours deterioriate, noise is introduced and the photo begins to look all wrong.

 

Old: 93,85,75,9

New: 97,76,53,2

Ideal: 99,75,50,2

standardsGH1_IncBaaderUVIRCut_081311wf_orig14pn101mid.jpg

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Be sure to let me know of any errors, typos, misapprehensions and other general goofs !! Thanks.
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I added another photo above - the original, unedited shot made with the 340AF15 to show the monochrome look when using a narrowband UV-pass filter.
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Question: On your 1.25" Spectralon standards, which image most closely resembles actual appearance to your eyes? (I ask because all I have are the 99% and 5%.)

 

This is interesting in relation to our recent discussions of Dyer's linear grey scale standards.

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Good question ! And I'll have to go look and get back to you.

 

If you are using the Spec standards for wideband documentary photography as we are doing here on UVP,

then I would think that the 99 & 5 are all you really need.

Those two would aid in setting the white/black points in photos with wide dynamic range.

And the white standard can be used for white balancing a shot.

 

Even though I indulged in a full $et of the$e $tandards, I can't say that I really use the 50 or 25% discs.

I do make use of the 75% disc because it is so easy to overexpose the 99% disc.

 

In retrospect (sigh), a 90% standard is probably more useful than a 99% for this kind of photography.

 

BTW, I probably would not set the white point at 99% brightness but a bit lower.

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I do make use of the 75% disc because it is so easy to overexpose the 99% disc.

 

Boy, it sure is easy to blow out the 99% and PTFE too! Hence my interest in the recipe for Dyer's linear grey scale standards. I do not think there is a 90% Spectralon, is there?

 

Update: I went and looked, no 90% but there is an 80% in 1.25" and 5"x5"($$$!!!).

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Probably if we took the time to spot meter the 99% disc and then set the exposure off that, it would be a good thing. :lol:

I have a button set up to quickly switch to spot meter on the Nikon, but I need to figure out how to do this on the Pentax.

 

The PTFE seems shinier, a bit easier to blow out.

 

I check the RGB histograms and luminance histogram frequently while shooting any of these standards.

 

No there isn't a 90% Spectralon. Oh well.

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John,

 

wiki says

 

"Kodak R-27 set, which contains two 8x10" cards and one 4x5" card which have 18% reflectance across the visible spectrum, and a white reverse side which has 90% reflectance"

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Zach, the Kodak R27 set is only for visible work. The reflectance is not stable under UV or IR.
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