Another WB question:)

Hi guys,

I have a few WB questions for you and would appreciate if anyone could help me with them

Q1
I have been using X-rite ColorChecker for some time know and I am quite happy with the way it helps me as far as colours are concerned. The only quibble I have got is the size of the grey card which is really small and I never know how much of it you should see in the viewfinder to make an in camera custom WB? Do I need to see the whole card, does it need to be in focus?

Q2
So I had orderd a bigger Lastolite 50cm grey card. It came today but to my suprise the grey is much darker the the grey on my Colorchecker

Q3
Another thing is, I have always thought that if you take a picture of a gray card with the correct exposure, it shoule be displayed in the middle of the histogram with R, B, G overlapping

Well, I have attached a screenshot of my histogram and my gray sits in the shadows.

What am I doing wrong?


.

If you photograph a neutral gray target, to set in-camera White Balance custom setting, it needs to fill the central circle (the spot zone).
If you photograph a neutral gray target, to sample during post processing to set White Balance, it needs only to be large enough to be sampled with the eye dropper tool.

The Lastolite gray could be either the original 18% gray, which is same as the fourth greyscale tone square on the bottom row of the Colorchecker card, or it might be the newer Lastolite EZ Balance 12, 12% gray (darker).

If you meter 18% gray, the photograph of that will actually be placed a little to the LEFT of center on the histogram! Like this

1. On the 5D2 you don't need to have the card fill the whole viewfinder, only the spot metering circle. It doesn't need to be in focus.

2. For WB purposes the shade of grey makes no difference as long as it is a truly neutral grey.

3. The camera is calibrated to 12.4% grey in the initial capture which after gamma correction translates to about 40% in the jpg. Thus the peak on your camera's histogram should be a little left of center, at 4 on a scale of 0-10. This is not the same as LR's histogram because LR processing is different from Canon processing. The color space is different, the profiles and tone curves are different, the default brightness is different, etc.

Tommy, what was your exposure mode when shooting the gray card? If you used an auto/semi-auto mode and either filled the frame with the gray card or used Spot Metering only on the gray card, the "standard" exposure the camera comes up with should show the gray slightly to the left of center in the histogram, like Wilt shows.

In fact, if you shoot with a centered needle for an evenly-toned target, the camera will, if possible, set the tone for your target to the "standard" exposure, "medium", meaning that it will lighten darker targets or darken lighter objects.

From your screen shot, the histogram appears as if you either had Exposure Compensation dialed down by a stop or in Manual, had the camera set for one stop "underexposed".

As to your question of focusing for shooting a White Balance target, you should set your lens to MF. In fact, for a solid-tone target (no contrast/details) you won't be able to AF on it! You don't need to focus, since you just need the neutral tone of the target, although if you want to you can MF!

tzalman wrote in post #14087270
3. The camera is calibrated to 12.4% grey in the initial capture which after gamma correction translates to about 40% in the jpg. Thus the peak on your camera's histogram should be a little left of center, at 4 on a scale of 0-10. This is not the same as LR's histogram because LR processing is different from Canon processing. The color space is different, the profiles and tone curves are different, the default brightness is different, etc.

But still, Elie, the histogram in LR should show the exposure, which should be "standard" if the meter was "centered" in the camera -- LR should show the histogram pretty close to what you see in the camera as far as the peak value...

tonylong wrote in post #14087300
But still, Elie, the histogram in LR should show the exposure, which should be "standard" if the meter was "centered" in the camera -- LR should show the histogram pretty close to what you see in the camera as far as the peak value...

Yes, I would expect it to be closer to 40% than the 30% in the OP's screen capture. The OP's camera might be underexposing. However, it's impossible to know which LR that is, 3 or 4. There may be a difference between them because LR4 does an automatic under-the-hood auto tone which is influenced by image content. I don't know if it will react to a solid grey frame differently than LR3. I'll take a look at it.

For WB the darkness doesn't matter, as long as the color is neutral. Size doesn't matter much either.

For metering and WB together a larger card is easier, and the card should be 18% grey.

I am currently using LR4 as a trial. The shot was taken in Manual mode. It is a bit weird as when I checked the exposure with my Sekonic there was only 1/3 stop of a difference between the camera and light meter reading. A bit confused now

OK, I tried it with my 5D2. The camera histogram had the peak at just to the right of the 40% line, call it 42%. LR4 (default settings, all 0) put it at 41% with the Camera Neutral profile and 43% with Adobe Standard. With the Neutral profile and soft-proofed for Adobe RGB (the camera is on Neutral P.S. and Adobe RGB) it become 42%. LR3 (default, Brightness 50, Contrast 25) made it Neutral 43% and Adobe Standard 45%. So insignificant differences.
[I have verified (only last week) that the camera ADC is calibrated to 12.4% in the linear RAW data (average grey card value 1,954 with a white point of 15,760 in 14 bits) which translates with a 2.2 gamma correction to 39%. So both the firmware and LR are making it about 1/3 of a stop lighter - not a big deal]

So if the OP had the needle centered his camera seems to be underexposing by about 2/3 of a stop.

So, yeah, like Elie said, you were underexposed!

tommmy.star wrote in post #14087639
I am currently using LR4 as a trial. The shot was taken in Manual mode. It is a bit weird as when I checked the exposure with my Sekonic there was only 1/3 stop of a difference between the camera and light meter reading. A bit confused now

And I'd say that you probably just got the wrong Manual settings.

But, check it out, simple stuff to test. Pick a plainly flat-colored wall, no details/decorations, and no uneven light on it. Frame a shot where the even color fills the frame, Manual Focus, and in Manual ensure that the meter needle is centered and take the shot.

Then switch to an auto/semi-auto mode and take the same shot ensuring that there is no Exposure Compensation set.

Then, try a wall with a different tone or lighting, but again even & no detail, and repeat, again in Manual and in an auto/seme-auto mode.

You can do the same with your gray card, although for this make sure it fills the frame, not just the center circle.

Compare the histograms in the camera and they should be very similar, with the "peak" just left of the center.

I don't have LR4, but from what Elie says there should not be a very noticeable difference -- the center spikes should all be just to the left of center.

Do this and you can at least settle whether your camera meter/exposure "estimates" are significantly off or not. You hear a lot of people claim that their camera "underexposes" or "overexposes" and that they keep there Exposure Compensation dialed up or down accordingly, but I'm pretty convinced that for most of those things they just don't fully grasp what the dang things are up to when it comes to exposure. Yes, Exposure Compensation can be a very useful tool in the semi-auto modes, but it's not helpful if you don't understand why you need it and how to use it!

Sorry Tony I don't get that. What wrong Manual setting are you refering to? I thought Manual is Manual and nothing else to it. I will do some more test when I get back home.

tommmy.star wrote in post #14089725
Sorry Tony I don't get that. What wrong Manual setting are you refering to? I thought Manual is Manual and nothing else to it. I will do some more test when I get back home.

"Manual" is a mode. "Manual settings" are ISO, f-stop, & shutter speed.

Need to start reading a bit slower and with more understanding

I have redone the test and today it looks way better. I don't know maybe it was the lighting (tungsten) which might have been slightly uneven.

Is this any better?

tommmy.star wrote in post #14091491
Need to start reading a bit slower and with more understanding

I have redone the test and today it looks way better. I don't know maybe it was the lighting (tungsten) which might have been slightly uneven.

Is this any better?

Sure, that's what would be a "standard" exposure -- you had the meter needle "centered". With your first shot you didn't.

I think you are making this more complicated than it needs to be!

I could swear the needle was centred in the first shot. I am just trying to get rid of the 'blame the gear' syndrome ( and pull the trigger for 5DIII Anyways, thanks a lot for all your support guys.
Tony you are a POTN hero. You have helped me loads of times so far. Great contributor.