Tech Question re Greycard WB

[dwbell]

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One for the technically versed.

 

If I set WB with a Greycard, why can't the camera tell me what the resulting Kelvin is? This is not limited to the M240, or Leica.

 

If it did I would be able to warm it up just a touch, usin direct K input knowing where 'correct' was. I'd also be able to pre-measure say the inside of the church, the signing room and reception area (for example), make a little note and go straight there in K settings - even put itin a preset with the relevant ISO!

 

So, why when I review custom WB image doesn't not say Cust3200k for example?

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[thighslapper]

I get very muddled with all this as well........

 

..... presumably the camera has no colour meter ..... and WB is derived from one of a number of algorithms for each image if using auto WB.

 

With a grey scale card it must use the same method ...... but just produces a set of correction factors for each of the colour channels to bring them all into line..... there is no K value as such.

 

What confuses me is the fixed WB settings ...... Colour meter, Camera and LR figures never coincide ....

[dwbell]

Yeah, that too!

 

I know what you mean, that it just looks at the RGB values of the target card and brings all three to match. Maybe taking the "middle value" o the three as the target or some such operation? And that this process is K value independent. It's just an equalising process.

 

But then, it's a computer right? Working to an algorithm? Just like my Mac is with Lightroom? Which DOES give me a value when I click with the WB tool. So why can't my little M240 computer? What has the mac got that the M240 hasn't? It doesn't have a colorimeter built in, and it's not process power dependent surely?

[sandymc]

Two problems - firstly, to specify white balance, you need both a color temperature and a tint value.

 

Color temperature alone is only sufficient for an ideal black body light source (aka for a black body source, the tint is always zero). As these are fairly rare in real world photographic situations, color temp alone isn't much use.

 

The second problem is that white balance varies depending on camera profile. So even if the camera gave you a color temp and tint, that wouldn't be accurate when you imported the raw image into LR or C1, which use their own camera profiles. This is why WB is specified as a color in the image, not as color temp/tint

 

Sandy

[dwbell]

That's interesting Sandy, thanks.

 

The difference between profiles and resulting values is what Thighslapper observes. But for my usage I don't care, I just want what the camera 'thinks' the temp and tint are so that I can either note them down, or increase temp relative to a known start point. Absolute accuracy is not required, just the value it thinks is neutral based on the grey card reading. I still don't see why this would not be possible in camera?

 

Or have I missed something?

[sandymc]

Well, what you want isn't unreasonable. The big "but" for a camera manufacturer would be all the questions that they would end up fielding (and unhappy users) when inputting a color temp from your M9 gave a different result in LR to what it gives in-camera. This is much the same as Leica hiding (mostly anyway) the estimated f-stop info - the golden rule is: "if it's likely to confuse customers, leave it out!!!" Adobe already spend half their life answering the "but the colors are different in LR to the in-camera JPEG" question.

 

If you really want, you can use e.g., PhotoRaw in the field on an iPad, take a look at what PhotoRaw thinks the color temp and tint are, and note that down. Of course (a) that involves an iPad, uploading and image onto it, etc. And (2) while PhotoRaw's temp/tint computation happens to be very similar to LR, it uses different camera profiles, so you still have the profile problem.

 

Sandy

[algrove]

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I was shooting with Grey card settings yesterday on my M. Worked well, but are we sure that every setting has a Kelvin equivalent.

[dwbell]

Well, what you want isn't unreasonable. The big "but" for a camera manufacturer would be all the questions that they would end up fielding (and unhappy users) when inputting a color temp from your M9 gave a different result in LR to what it gives in-camera. This is much the same as Leica hiding (mostly anyway) the estimated f-stop info - the golden rule is: "if it's likely to confuse customers, leave it out!!!" Adobe already spend half their life answering the "but the colors are different in LR to the in-camera JPEG" question.

 

If you really want, you can use e.g., PhotoRaw in the field on an iPad, take a look at what PhotoRaw thinks the color temp and tint are, and note that down. Of course (a) that involves an iPad, uploading and image onto it, etc. And (2) while PhotoRaw's temp/tint computation happens to be very similar to LR, it uses different camera profiles, so you still have the profile problem.

 

Sandy

 

True, true. But they already give values for Daylight, Shady, Tungsten, don't they? Which as mentioned don't exactly match, and that doesn't cause too much grief I don't believe. One can use a cumbersome work around of manually entering K value, taking a grey card shot, zooming in with RGB histo and adjusting the three peaks to taste iteratively, so to speak. This uses the jpeg profile etc so is a rough shot for sure.

 

@algrove - I think we're sure, aren't we? Has to be a temp and tint.

[algrove]

greycard is for setting what is the grey the light meter is looking for, no? Remember you can move the crosshairs to the shade of grey you want.

[dwbell]

greycard is for setting what is the grey the light meter is looking for, no? Remember you can move the crosshairs to the shade of grey you want.

 

Ah, I see. No, there are two things referred to as 'grey card' - and likely I'm using the term incorrectly (which will please 0laf! )

 

There's 18% grey cards, which are used for reflective metering and exposure setting. And there's neutral grey cards which are colour neutral, for setting the WB in camera. You can't use one for the others purpose.

 

I am, however, referring to the neutral WB grey card, such as a WhiBal etc.

[MirekE]

One for the technically versed.

 

If I set WB with a Greycard, why can't the camera tell me what the resulting Kelvin is? This is not limited to the M240, or Leica.

 

If it did I would be able to warm it up just a touch, usin direct K input knowing where 'correct' was. I'd also be able to pre-measure say the inside of the church, the signing room and reception area (for example), make a little note and go straight there in K settings - even put itin a preset with the relevant ISO!

 

So, why when I review custom WB image doesn't not say Cust3200k for example?

 

The color temperature and tint values have meaning only in calibrated RGB. The camera has embedded profile and I believe the firmware could in theory calculate the values for the temperature and tint. But these values would be only valid for the embedded profile. To my knowledge, the DNG file does not contain temperature and tint data, but three "As Shot Neutral" values that are used to scale the raw data when calculating the RGB values in raw converter.

[dwbell]

Seems to suggest that what I would like to see is perfectly possible?

 

When I import my custom WB grey card shots into LR and click the white balance dropper on the card in the shot, nothing happens, or at least no huge change, maybe a point here or there in tint and a 100 or so shift in temp. So the difference between 'as shot' and another profile is negligible enough for my purposes.

 

I know they won't do it - it seems to be only me who's interested in the value the camera thinks is neutral for a given setting. But I'm interested to find out if it would be theoretically possible.

[wda]

If you shoot in artificial lighting and include your grey card, you should see a clear correction when sampling in LR.

 

I usually make a shot of the entire grey card using the WB menu setting. Then all ensuing shots under the same or similar lighting will be standardised to that WB. Just remember to reset when lighting changes. That is where I find User Profiles so useful. You can quickly reset to known values.

[dwbell]

Yeah, know all that. I meant importing the grey card shot used to create the custom WB in the first place creates very little change in LR - such that the embedded profile and the LR profile are close enough for jazz was my point.

[wda]

The act of setting a custom white balance produces a file which is spectrally neutral and therefore you won't see a change when imported into LR.

[dwbell]

The act of setting a custom white balance produces a file which is spectrally neutral and therefore you won't see a change when imported into LR.

 

Yes. Sorry wda, maybe I'm not being clear? I know that. I'm saying that because there is no significant change when you import that file into LR then why can LR on a mac/pc give me a tint and temp but the camera can not. It was suggested that it was embedded profile related earlier in this thread, I'm suggesting the differences are so minor (pertaining to the profile) that in theory it should in fact be possible to tell me the WB in camera after setting a custom WB. Or indeed, can anyone correct me otherwise?

[sandymc]

Practically, on an M9 and using LR, I've seen the following:

 

Embedded profile: 8300 K.

Adobe Standard profile: 6900 K

 

Only a 1400K difference.

 

Admittedly an extreme case because the temp was high, but the difference can be substantial.

 

Sandy

[dwbell]

Practically, on an M9 and using LR, I've seen the following:

 

Embedded profile: 8300 K.

Adobe Standard profile: 6900 K

 

Only a 1400K difference.

 

Admittedly an extreme case because the temp was high, but the difference can be substantial.

 

Sandy

 

Indeed! I've not seen that big a shift in my work. Although I'm not always looking to identify it per se. So maybe it's happened and I've not noticed.

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[thighslapper]

That's par for the course with the M at higher K values ....... they seem to behave semi logarithmically the higher you go ..... with very small discernible differences (to the eye) despite big jumps in K value....

[tobey bilek]

A grey card is not necessarily 128 each RGB. It is made as an exposure device, not WB device.

 

Whi Bal cards are made neutral. I set the WB off them and save it as a profile in camera. The camera will record 4 profiles, so I have one custom WB for sun, cloudy, flash, one for 3200K. I can do a custom WB for a series if I place a Whi Bal card in one frame.

 

Step two is to profile the camera with Adobe profile editor. then all the colors are perfect.

 

Balancing off a Whi Bal card will set the tint or RED/cyan & green/magenta. K only does blue yellow.