Gray card and exposure

[peerke]

Hi,

I am trying to come to grips with the colorchecker passport and the use of the gray card (in LR3). Since I am relatively new to all this I hope someone can explain the following phenomenon, or give me a pointer to an explanation (could not find it here yet).

If I take two picture of the 18% gray card with different exposures and then use the white balance selector to determine a white balance point, I get two substantially different color temperatures. The longer exposure (0.3 sec, 3800) gives a higher temperature than the shorter exposure (1/13 sec, 3600)In my naive expectation I would expect that if the only parameter that changes is the exposure time, then the color temperature would stay the same?

Can anyone give me a clue why this happens?

Rgds,
Tom

[digitaldog]

For starters, the tool in LR is a white balance, not a gray balance tool, so use the appropriate patch (2nd lightest white patch).

[Raw shooter]

For starters, the tool in LR is a white balance, not a gray balance tool, so use the appropriate patch (2nd lightest white patch).

Rodney, is there any problems using the whitest patch - especially with newer cameras and a perfect exposure (whitest patch is safely below 255, 255, 255 and not underexposed either) of the white balance card.  I have been using the second patch for years with my Color Checker cards, but Xrite released a large version of their White Balance Card and it was the whitest patch and not the second patch as I had expected.
Either way, in Camera Raw, the White Balance tool sees my flash as different WB (>100) based on which patch is used a reference.

[digitaldog]

Rodney, is there any problems using the whitest patch - especially with newer cameras and a perfect exposure (whitest patch is safely below 255, 255, 255 and not underexposed either) of the white balance card.  I have been using the second patch for years with my Color Checker cards, but Xrite released a large version of their White Balance Card and it was the whitest patch and not the second patch as I had expected.
Either way, in Camera Raw, the White Balance tool sees my flash as different WB (>100) based on which patch is used a reference.

IF the white is too white, ACR or LR will pop an error hence the 2nd white is usually recommended (a non specular white is ideal).

[peerke]

For starters, the tool in LR is a white balance, not a gray balance tool, so use the appropriate patch (2nd lightest white patch).

Hi Andrew,

Thanks for your reply. I was under the impression that 'The ColorChecker White Balance Target' could be used for this purpose, and that the requirement for the LR White Balance tool was that the patch is neutral, not white. What am I missing here? And it looks like the 2nd patch is, like the white balance target, 18% gray?



Tom

[digitaldog]

Hi Andrew,

Thanks for your reply. I was under the impression that 'The ColorChecker White Balance Target' could be used for this purpose, and that the requirement for the LR White Balance tool was that the patch is neutral, not white. What am I missing here? And it looks like the 2nd patch is, like the white balance target, 18% gray?

Neutral by all means. While you could use a gray, its more likely you’ll end up with a cast and, because half all the data in a raw linear encoded file is in the highlights, the recommendation is to WB while in a gamma corrected image, the recommendation to gray balance.

[Steve Weldon]

Hi,

I am trying to come to grips with the colorchecker passport and the use of the gray card (in LR3). Since I am relatively new to all this I hope someone can explain the following phenomenon, or give me a pointer to an explanation (could not find it here yet).

If I take two picture of the 18% gray card with different exposures and then use the white balance selector to determine a white balance point, I get two substantially different color temperatures. The longer exposure (0.3 sec, 3800) gives a higher temperature than the shorter exposure (1/13 sec, 3600)In my naive expectation I would expect that if the only parameter that changes is the exposure time, then the color temperature would stay the same?

Can anyone give me a clue why this happens?

Rgds,
Tom

Ideally you want to use the gray slab on the Color Checker Passport to set a custom white balance as your first step in the field.  Step two in the field is a second capture of the color checker card itself under the same lights.   Step three is using that color checker card to build a color profile for that series of shots inside LR (export to Color Checker Passport)..  If you do it in this order you won't need to use the WB eyedropper unless you wish to warm the temp up a bit.

I've found this combination extremely accurate.. and the 'warming squares' an excellent way to alter that accurate color to suit your tastes.  As we know, the most accurate white balance isn't necessarily the best one.. but it sure helps to start from that point.

[peerke]

Ideally you want to use the gray slab on the Color Checker Passport to set a custom white balance as your first step in the field.  Step two in the field is a second capture of the color checker card itself under the same lights.   Step three is using that color checker card to build a color profile for that series of shots inside LR (export to Color Checker Passport)..  If you do it in this order you won't need to use the WB eyedropper unless you wish to warm the temp up a bit.

I've found this combination extremely accurate.. and the 'warming squares' an excellent way to alter that accurate color to suit your tastes.  As we know, the most accurate white balance isn't necessarily the best one.. but it sure helps to start from that point.

Hi Steve,

That is exactly the procedure I followed. First take the WB target to set the in-camera white balance, and then use a picture of the color checker card to create a profile within LR. I am a bit puzzled though if setting the in-camera WB is really necessary if one is shooting RAW. Using the eyedropper is easier in my perception.

Tom

[Steve Weldon]

Hi Steve,

That is exactly the procedure I followed. First take the WB target to set the in-camera white balance, and then use a picture of the color checker card to create a profile within LR. I am a bit puzzled though if setting the in-camera WB is really necessary if one is shooting RAW. Using the eyedropper is easier in my perception.

Tom

There are a few things which happen in order this way..

1.  You're setting a custom white balance

2.  You're using thats custom white balance to take the second capture of the color checker itself

3.  This gives you the most accurate profile..

I've tried it both ways.. and there is a difference.   How much of a difference depends on how close your AWB or non-custom WB is to what it should be.

Sure, you can get around it.. but this is the way it was designed and really.. unless you just forget (it happens), setting a custom wb in the field is a very simple and  quick procedure.  With my Canon 5d Mark II I put the menu items I need in the custom menu.. makes it even faster.

If you do set your WB back in LR after the fact.. then make sure you adjust then change the image of your color checker to the proper WB BEFORE running the profile.

All in all.. this is one case where having someone read the instructions to me was probably worth it..

[peerke]

There are a few things which happen in order this way..

1.  You're setting a custom white balance

2.  You're using thats custom white balance to take the second capture of the color checker itself

3.  This gives you the most accurate profile..

I've tried it both ways.. and there is a difference.   How much of a difference depends on how close your AWB or non-custom WB is to what it should be.

Sure, you can get around it.. but this is the way it was designed and really.. unless you just forget (it happens), setting a custom wb in the field is a very simple and  quick procedure.  With my Canon 5d Mark II I put the menu items I need in the custom menu.. makes it even faster.

If you do set your WB back in LR after the fact.. then make sure you adjust then change the image of your color checker to the proper WB BEFORE running the profile.

All in all.. this is one case where having someone read the instructions to me was probably worth it..

Hi Steve,

That makes an awful lot of sense, especially the last remark  

Takes me back to my original question though. Why does the color temperature change with changing exposure time?

Tom

[Steve Weldon]

Hi Steve,

That makes an awful lot of sense, especially the last remark  

Takes me back to my original question though. Why does the color temperature change with changing exposure time?

Tom

It's probably not changing.. any two shots of the gray card, even at the same exposure time, will probably yield slightly different WB readings due to the angle you're shooting changing a lot, a cloud passing over, a shadow.. a lot of reasons are possible.. but not exposure time.  Do some testing and give it a try..

[digitaldog]

I am a bit puzzled though if setting the in-camera WB is really necessary if one is shooting RAW.

None at all. For JPEG of course. The WB camera setting is simply a metadata suggestion for a raw converter (and each will render the WB differently). All the camera settings for sharpness, picture styles, color space and WB play no role or affect the raw data.

[Steve Weldon]

None at all. For JPEG of course. The WB camera setting is simply a metadata suggestion for a raw converter (and each will render the WB differently). All the camera settings for sharpness, picture styles, color space and WB play no role or affect the raw data.

I agree with this with one caveat if only shooting a gray card.  The caveat being that if the actual WB is so far out from the set WB, depending on the camera, it is possible to end up with a clipped color channel when adjusting in raw.  I've only seen this happen under extreme conditions and it's usually the red channel, but it does happen.

But the question involves using the color passport.. Instructions say shoot the grey card first, set your custom WB, and then shoot the color checker.

Are they doing this because the custom WB then provides the most accurate color checker capture for use in building your profile, or because they think this is an easier way to remember vs. counting on people to remember to adjust the color checker WB prior to building the profile.. or does it just work better?

I've done both because even though I shot the grey slab.. I then forgot to set the custom WB..  So I used the grey slab to set WB or the white squares.. then changed the WB accordingly on the color checker image.. then built the profile.  Really, it's possible to just shoot the color checker and use the white squares on it to set WB, then run the profile builder.. but if this is a better way.. or makes no difference.. why did Xrite go to all the expense/trouble of including the grey slab and make their product more complicated than it needs to be?

My observation is it 'appears' to make a difference if you follow the directions.  I get very accurate skin tones this way.  Adjusting WB after the fact don't seem to be as accurate.  Why?  It could be the sequence, or it could be the way I set WB in LR..

[digitaldog]

But the question involves using the color passport.. Instructions say shoot the grey card first, set your custom WB, and then shoot the color checker.

IF the instructions don’t mention raw vs. JPEG, they should because the first step isn’t necessary for raw and what you click on would depend on the data you are working with.

Are they doing this because the custom WB then provides the most accurate color checker capture for use in building your profile, or because they think this is an easier way to remember vs. counting on people to remember to adjust the color checker WB prior to building the profile.. or does it just work better?

Again, it plays zero role in the raw data itself. And accurate is a term that raises the hair on the back of my neck without a well structured definition. Accurate in that the results using this will be more colorimetrically correct because I kind of doubt that. Accurate in that you might get a more preferable color appearance of an embedded JPEG the camera made inside the raw?

[Steve Weldon]

IF the instructions don’t mention raw vs. JPEG, they should because the first step isn’t necessary for raw and what you click on would depend on the data you are working with.



Again, it plays zero role in the raw data itself. And accurate is a term that raises the hair on the back of my neck without a well structured definition. Accurate in that the results using this will be more colorimetrically correct because I kind of doubt that. Accurate in that you might get a more preferable color appearance of an embedded JPEG the camera made inside the raw?

I'll agree that 'accurate' when used on these terms is a flexible at best but for lack of a better word..

Perhaps the instructions do assume jpegs..  But my question and observation remains, does taking the capture of the color checker, subsequent to setting an accurate custom white balance, achieve a different result than simply adjusting the WB in raw and then applying it to the color checker capture prior to building the color profile?

My observations are it does make a difference.. using skin tones as an example I get a more accurate (looks more like the actual real skin tones) WB and resulting profile if I use their gray slab to set a custom WB in the camera prior to making the color checker capture.

It could be that using their grey slab with the in-camera custom WB function produces a more accurate WB than you can get using the grey slab or white squares in a raw processor after the fact.. or it's easier to be accurate.. and I suppose this would depend on the camera and/or operator skill in the raw processor.

To be honest though.. when I watched the xrite tutorial video.. I didn't notice if they were actually working with RAW files or not, I just assumed they were.. functionally it wouldn't make a difference in LR.. but it might in the ultimate image quality.

[Steve Weldon]

IF the instructions don’t mention raw vs. JPEG, they should because the first step isn’t necessary for raw and what you click

I was just playing with several shoots using the color checker passport.. did it both ways.  

I think maybe.. perhaps.. I have some insight..

Using the eye droper you can click on different parts of the grey slab.. or white squares.. and get different readings.  Of course the grey slab varies the most as you'd expect.  

Depending how well refined the in camera custom white balance is.. it is probably sampling a much larger area than the eye dropper does in raw.  Providing an 'overall' more accurate WB reference.

[Raw shooter]

I'll agree that 'accurate' when used on these terms is a flexible at best but for lack of a better word..

Perhaps the instructions do assume jpegs..  But my question and observation remains, does taking the capture of the color checker, subsequent to setting an accurate custom white balance, achieve a different result than simply adjusting the WB in raw and then applying it to the color checker capture prior to building the color profile?

My observations are it does make a difference.. using skin tones as an example I get a more accurate (looks more like the actual real skin tones) WB and resulting profile if I use their gray slab to set a custom WB in the camera prior to making the color checker capture.

It could be that using their grey slab with the in-camera custom WB function produces a more accurate WB than you can get using the grey slab or white squares in a raw processor after the fact.. or it's easier to be accurate.. and I suppose this would depend on the camera and/or operator skill in the raw processor.

To be honest though.. when I watched the xrite tutorial video.. I didn't notice if they were actually working with RAW files or not, I just assumed they were.. functionally it wouldn't make a difference in LR.. but it might in the ultimate image quality.

I have a hard time following this.  How can an "in-camera" custom White balance play any role in the raw data captured as a camera raw file. They have no relationship in the image raw data.  A simple metadata recommendation for a raw converter still doesn't change the raw file data at all.  Raw is raw - camera settings that are applied to JPG or TIFF captures-  don't affect the raw data at all.

[Steve Weldon]

I have a hard time following this.  How can an "in-camera" custom White balance play any role in the raw data captured as a camera raw file. They have no relationship in the image raw data.  A simple metadata recommendation for a raw converter still doesn't change the raw file data at all.  Raw is raw - camera settings that are applied to JPG or TIFF captures-  don't affect the raw data at all.

We've already went through a few posts since this one.. That "in-camera" white balance is probably sampling a much larger area (according to the 5d Mark II manual, the entire spot metering circle) and perhaps coming up with a better recommended setting than using the small area an eyedropper does in a raw converter.  

Or maybe they just want to make sure the WB is corrected on the color checker shot prior to building the profile. The color checker profile builder seems to take all the colored squares into account when building the profile, I don't think it's smart enough to isolate one, set the WB, and then build the profile.


Further.. I still maintain that if you're WB is really far off when making a capture, you could end up clipping a color channel.  It depends on the camera, and how far to each side of the medium data is captured.. or what I call how "fat" the file is.  Better DSLR's seem to have fatter files.. the budget ones not so much.

[shewhorn]

Hi,

I am trying to come to grips with the colorchecker passport and the use of the gray card (in LR3). Since I am relatively new to all this I hope someone can explain the following phenomenon, or give me a pointer to an explanation (could not find it here yet).

If I take two picture of the 18% gray card with different exposures and then use the white balance selector to determine a white balance point, I get two substantially different color temperatures. The longer exposure (0.3 sec, 3800) gives a higher temperature than the shorter exposure (1/13 sec, 3600)In my naive expectation I would expect that if the only parameter that changes is the exposure time, then the color temperature would stay the same?

Can anyone give me a clue why this happens?

Rgds,
Tom

What was the light source? Fluorescent lights (depending upon the ballast used) typically pulse just below 60 Hz in the US (or 50 Hz depending upon the country you're in). Usually the effects of this can be mitigated by shutter speeds that are greater than 1/60th of a second although it wouldn't surprise me if shutter speeds that weren't even divisions of 1/60th (so 1/60th, 1/30th, 1/15th, etc.) could produce slight variations in color temp.

Cheers, Joe

[peerke]

What was the light source? Fluorescent lights (depending upon the ballast used) typically pulse just below 60 Hz in the US (or 50 Hz depending upon the country you're in). Usually the effects of this can be mitigated by shutter speeds that are greater than 1/60th of a second although it wouldn't surprise me if shutter speeds that weren't even divisions of 1/60th (so 1/60th, 1/30th, 1/15th, etc.) could produce slight variations in color temp.

Cheers, Joe

Hi Joe,

It was daylight and the gray card was in a light tent to make the light diffuse. The shots were taken after each other, so I imagine I can only blame fluctuations in a lightbulb some 149.600.000 km kilometers away. Come to think of it, even though it was quite sunny, moving clouds could give a more obvious explanation...  

Tom