Grey card VS what my eyes (brain) sees

[cichlid]

Hi All,

So I have an interesting project coming up where samples will need to be graded based on the difference of their color.

A white background will be use for optimum contrast.

The tutorial here, I believe, has answered my question, but would like to confirm here. Our brains are good at determining what is white under different qualities of lighting (tungsten, florescent etc.). When we use a grey card, we calibrate the camera to see white as white in various types of lighting conditions.

So, when I take my photos under florescent light, I will calibrate my camera under the same conditions, print from a calibrated printer (and monitor) and I should see identical colors from the live sample and printed version right?

Now, lets say that those same samples are under florescent light that is passed through a yellow filter. How can I tell my camera not to correct for the yellow as I want the camera to see the same yellow as we would see in the room?

Thank you for your responses.

Erik

[Colin Southern]

Hi Erik,

What you describe is what I call "technically correct" white balancing. The other sort is what I'll call "visually correct" white balancing (eg a sunset, where it's adjusted to look good as opposed to being technically correct).

The short answer to your question though is - if you shoot RAW - then you can losslessly adjust the white balance to anything you like (no need to "calibrate" the camera first), although it does help to have a spectrally neutral reference in the scene.

[revi]

...

So, when I take my photos under florescent light, I will calibrate my camera under the same conditions, print from a calibrated printer (and monitor) and I should see identical colors from the live sample and printed version right?

Now, lets say that those same samples are under florescent light that is passed through a yellow filter. How can I tell my camera not to correct for the yellow as I want the camera to see the same yellow as we would see in the room?

I'd say you have a few possibilities, depending on what you want exactly:
- either use a color/WB target under the unfiltered fluorescent light, to set a custom WB, and use that setting for the pictures taken under the yellow-filtered fluorescents.
- or if that's impossible, use (one of) the fluorescent settings on your camera.
Caveat: be careful to set your custom WB under the same type of fluorescents as will be used for the final shots (ideally: remove the yellow filter to set the WB/shoot the target).
And, in any case, document in as much detail as possible what exactly you have done, both while shooting and afterwards in post processing.

I gather from the question that you need technically correct colours, so I guess using a colour target could be useful here (colour passport or such). That would allow camera calibration.
I'd also include a shot of the target under the yellow light (better safe than sorry).

In any case, you'll have to make sure to get a reference shot with what you (want to) define as 'white' light, and use that to calibrate your shots under yellow light.

You still can get surprises when comparing the results of 'live' grading with grading based on photos, due to the differences in colour response between eye and camera.

Hope this helps,

Remco

P.S. In this situation you cannot set the WB to anything you like, as the job requires colour fidelity (sounds like a scientific setting). And, in this particular case of shooting under
coloured light, you cannot even have a white reference in your shots (as you want to see the effect of the yellow filter...), so you have to have a fixed and documented WB setting.

[cichlid]

Thank you Colin and Remco,

Thankfully, a decision was taken to not take photos under the yellow light.
The route we will take at the moment will be to shoot the grey card (as that is what we have available) as our reference, then take photos of the samples. We will print from several different printers and have several people grade the samples.

I'm curious to see the results.

[rpcrowe]

At the recommendation of Donald, I recently purchased and began using the WhiBal card ( http://www.whibalhost.com/_Tutorials/WhiBal/01/ ) and I love it.

However, I don't allow this card to overrule my eyes for color balance. The WhiBal card brings me within the ballpark of correct color values. However "correct" is not always the best.

I often prefer, especially in human portraits, to use a slightly warmer rendition than the correct color balance. This is often more pleasing to my eye.

Note: when making any color judgements, it is critical to have a color corrected monitor. If you do not correct the color of your monitor you are shoveling sand against the tide (as the saying goes). Because, there is no earthly way that you can determine if the color balance you have selected is what you really have.

I am still confused as to the color correction I would want to select for both getting accurate prints from my printer AND for publishing on the Web...

[xpatUSA]

Hi All,

So I have an interesting project coming up where samples will need to be graded based on the difference of their color.

A white background will be use for optimum contrast.

If you are using the same white background for each picture, such as a white cloth, it can serve as your means of custom white balancing (provided that it is not over-exposed but, in any case, the purpose of the project dictates that there should be no over-exposure anywhere in each image). People might say that's not right because the sample colors may not be precisely and exactly correct when viewed - but for a comparative test the white sheet should do it.

Some people would recommend halogen or flash for lighting, saying that other means of lighting such as fluorescent do not have even power spectra and could cause color mis-interpretation for this project.

As to not correcting for the yellow filter - you could set your camera's custom white balance to the white or gray target with the fluorescent lamp un-filtered, then add the filter and take the shots. You would not then correct the white balance during post-processing because there wouldn't be any white to balance!

Ted