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10-10-2019, 02:53 AM   #1
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Manual White Balance Not Giving Temp

Only now just getting into this, I noticed that the MWB feature of my K-1, when used (with a grey card), it will actually correct the WB but it never gives a value of temperature for room/environment you're 'looking' at.

I saw this video here;


And so I also tested the feature out, I was hoping to get something like this;

Flash Photography Tutorial : How to use Color Correction Gels with Strobes - YouTube

(looks like the Sony gives the temp, 4500k or the 4800k figure below, not sure but you get the point). This would be handy from a gelling perspective, if you get the temp from using MWB then you can match it up closely with the appropriate gel needed for flashing.

So... I'm just double checking this is right, that Pentax do not support this? I even checked in Detailed view of the playback of one of the MWB shots but still its not telling me the temp. Bit disappointing Pentax!

10-10-2019, 03:28 AM - 2 Likes   #2
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Can I know the temperature set in a Manual White Balance profile (in camera)? - PentaxForums.com

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10-10-2019, 06:14 AM - 1 Like   #3
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Color temperature is a one-axis color balancing system that only works with some light sources.

MWB is a two axis color balancing system -- adjusting the color on both a blue-amber axis and a magenta-cyan axis. Thus Pentax doesn't give the temperature of MWB because it would be inaccurate.
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QuoteOriginally posted by BruceBanner Quote
Manual White Balance Not Giving Temp
Yes, this is true. Doing manual WB actually generates correction factors that are not readily or reliably back-calculated to Kelvin degrees.


Steve


Last edited by stevebrot; 6 Days Ago at 09:58 AM.
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Just curious, does any other vendor display kelvin values in camera?
6 Days Ago - 1 Like   #6
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QuoteOriginally posted by K1N8 Quote
Just curious, does any other vendor display kelvin values in camera?
If they do, they are probably incorrect, unless the light source is a "black body," as noted by photoptimist and Steve above.

Look at this frame from the Wikipedia article on black-body radiation (Black-body radiation - Wikipedia)

https://en.wikipedia.org/wiki/Black-body_radiation#/media/File:PlanckianLocus.png

Note the "planckian locus." It's just a line through color space, whereas a light source might well fall anywhere in there (such as a non-"warm" LED that would have relatively a lot more blue emission).
6 Days Ago   #7
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QuoteOriginally posted by K1N8 Quote
Just curious, does any other vendor display kelvin values in camera?
Yes the Sony seems to, as shown in the video above that I linked.

QuoteOriginally posted by photoptimist Quote
Color temperature is a one-axis color balancing system that only works with some light sources.

MWB is a two axis color balancing system -- adjusting the color on both a blue-amber axis and a magenta-cyan axis. Thus Pentax doesn't give the temperature of MWB because it would be inaccurate.
QuoteOriginally posted by stevebrot Quote
Yes, this is true. Doing manual WB actually generates correction factors that are not readily or reliably back-calculated to Kelvin degrees.


Steve
Wait up tho... I get the whole 'approximation' and all that, but the Sony camera seen in the video I linked above seems to have no problem to giving a Kelvin approximation for MWB, and I'm certain when we take that RAW file snapped of a scene with MWB then LR will display the WB temp used at the time the shot was taken (after calibration), so really... from my perspective this is a cop out by Pentax. You can find the values of Kelvins for the presets for WB in a camera (Daylight, Tungsten etc), and of course we get to manually dial it in, but for some reason using a MWB that info is just hidden?! I really have to stop the shoot, eject the SD card from the camera, copy image across to PC, open the file in LR, see what WB temp it actually is... put SD card back in camera and then select an approximate gel to use for my flash... LOL! If you ask me it's another 'lets forget about flash stuff entirely' Pentax issue.


QuoteOriginally posted by AstroDave Quote
If they do, they are probably incorrect, unless the light source is a "black body," as noted by photoptimist and Steve above.

Look at this frame from the Wikipedia article on black-body radiation (Black-body radiation - Wikipedia)

Black-body radiation - Wikipedia

Note the "planckian locus." It's just a line through color space, whereas a light source might well fall anywhere in there (such as a non-"warm" LED that would have relatively a lot more blue emission).
It might be inaccurate, but it might be in the ball park close enough to allow someone to select an approximate gel to use for the scene (gels after all are approximation stuff themselves. You might not have a 3000k gel but you have a 3200k gel so you use that etc.
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And how would any DSLR or MILC accurately measure colour temperature without some reference? I had some photos shot in very mixed lighting (try getting a real value of colour temp. there!) and Photoshop/Camera Raw got very pleasing results by picking a known white surface and letting the tool correct the colour balance in post. It certainly wasn't by assigning a crude colour temperature value.

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QuoteOriginally posted by BruceBanner Quote
Wait up tho... I get the whole 'approximation' and all that, but the Sony camera seen in the video I linked above seems to have no problem to giving a Kelvin approximation for MWB
So what happens when the displayed value on the Sony is used to manually set the camera by Kelvin degrees? Are the results the same? (Evaluation would require a colorchecker or similar.) As noted above by @AstroDave, white balance by K is seldom accurate either. The spectra at the various isotherms on the Planckian locus are very specific and only approximated by other than black body emitters.



For what it's worth, in the real world we actually work with something called "correlated color temperature" which is a perceptual standard and hard to wrap the mind around (https://en.wikipedia.org/wiki/Color_temperature#Correlated_color_temperature).


Steve

Last edited by stevebrot; 6 Days Ago at 01:37 PM.
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QuoteOriginally posted by StiffLegged Quote
And how would any DSLR or MILC accurately measure colour temperature without some reference?
Using a gray card as a reference, the camera might come close. Otherwise, it just extrapolates from values in its lookup tables. Pentax includes similar in its makernotes.


Steve
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QuoteOriginally posted by StiffLegged Quote
And how would any DSLR or MILC accurately measure colour temperature without some reference? I had some photos shot in very mixed lighting (try getting a real value of colour temp. there!) and Photoshop/Camera Raw got very pleasing results by picking a known white surface and letting the tool correct the colour balance in post. It certainly wasn't by assigning a crude colour temperature value.
QuoteOriginally posted by stevebrot Quote
So what happens when the displayed value on the Sony is used to manually set the camera by Kelvin degrees? Are the results the same? (Evaluation would require a colorchecker or similar.) As noted above by @AstroDave, white balance by K is seldom accurate either. The spectra at the various isotherms on the Planckian locus are very specific and only approximated by other than black body emitters.



For what it's worth, in the real world we actually work with something called "correlated color temperature" which is a perceptual standard and hard to wrap the mind around (Color temperature - Wikipedia).


Steve
QuoteOriginally posted by stevebrot Quote
Using a gray card as a reference, the camera might come close. Otherwise, it just extrapolates from values in its lookup tables. Pentax includes similar in its makernotes.


Steve
I dunno... I feel like maybe there's some confusion here?

From both videos I linked, the intent of Manual White Balance IS to use a grey card to get an approximation of decent WB for a tricky scene. The Sony (once you use the grey card) not only changes the WB around that selection but will also pass the WB temp it has chosen, which is very good as it then lets someone know a colour temp gel to use to match the room.

The Pentax Manual White Balance is the same, you are to use a grey card and then it will 'correct' the WB. Everything is an approximation, we don't need abdsolute specifics in this regard, the bottom line is that when taking a RAW file shot with in Manual White Balance used it most definitely will have a Kelvin temperature, it just sucks that it's not even in the Detailed playback view of the file. This sucks!
6 Days Ago   #12
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QuoteOriginally posted by BruceBanner Quote
I dunno... I feel like maybe there's some confusion here?

From both videos I linked, the intent of Manual White Balance IS to use a grey card to get an approximation of decent WB for a tricky scene. The Sony (once you use the grey card) not only changes the WB around that selection but will also pass the WB temp it has chosen, which is very good as it then lets someone know a colour temp gel to use to match the room.

The Pentax Manual White Balance is the same, you are to use a grey card and then it will 'correct' the WB. Everything is an approximation, we don't need abdsolute specifics in this regard, the bottom line is that when taking a RAW file shot with in Manual White Balance used it most definitely will have a Kelvin temperature, it just sucks that it's not even in the Detailed playback view of the file. This sucks!
Not everything is an approximation. It's "color temperature" that is a very poor approximation of white balance for most of the light sources found in the modern world. I agree with Steve's hypothesis is that Sony's reported "Color Temperature" number would not be useful for the purpose of picking gels to match it.

That said, I agree with you that it would be nice if Pentax' MWB implementation provided some indication of where a given measured MWB is on the blue-amber and magenta-cyan axes. If it did that, you could do your own measurements of each gel, write them down, and then know which one to use when you measured the scene.
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QuoteOriginally posted by BruceBanner Quote
From both videos I linked, the intent of Manual White Balance IS to use a grey card to get an approximation of decent WB for a tricky scene. The Sony (once you use the grey card) not only changes the WB around that selection but will also pass the WB temp it has chosen, which is very good as it then lets someone know a colour temp gel to use to match the room.
So...what happens if you plug the displayed K back into the camera? Do you get the same result?

I am serious.

QuoteOriginally posted by BruceBanner Quote
the bottom line is that when taking a RAW file shot with in Manual White Balance used it most definitely will have a Kelvin temperature
This is not true. A manual gray card WB setting results in four color correction factors, (1R, 2G, 1B) that are applied as part of RAW processing. The numbers are what is required to render equal values for the set of (RGGB) pixels in the Bayer matrix (result = gray) within the sampled area and nothing more. Manual entry of K value results in the same four numbers, but may not result in the same four numbers as a gray card measurement even if illumination is from a standard light source. It may not be obvious, but the relationship of white balance to a K isotherm spectrum on the camera side of things is purely coincidental and tied to historic color film response specifications.


Steve

Last edited by stevebrot; 6 Days Ago at 02:46 PM.
6 Days Ago   #14
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QuoteOriginally posted by photoptimist Quote
That said, I agree with you that it would be nice if Pentax' MWB implementation provided some indication of where a given measured MWB is on the blue-amber and magenta-cyan axes. If it did that, you could do your own measurements of each gel, write them down, and then know which one to use when you measured the scene.
That might be nice, though the usual tool is not a camera; rather, it is a dedicated color meter or an incident light meter supporting color meter functionality.


Steve

Last edited by stevebrot; 6 Days Ago at 03:03 PM.
6 Days Ago   #15
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QuoteOriginally posted by BruceBanner Quote
This sucks!
OK...here is a workaround...

1. Save off the manual white balance to file
2. Open the file in Lightroom and modify the WB using the develop module with a small change, say +1 K.
3. Read the resulting K from LR display and subtract the change.

The result is based on a back-calculation of the correction factors in the EXIF and should be fairly close. I have not tested this (need to go out and trim some trees), but it should work, perhaps even in LR mobile.


Steve
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