exposure and lightroom

[kanuski]

I have read about people using Lightroom to check to see if the exposure on a models face is correct. How is this done?

 

[Ysarex]

Only in their fauxtography fantasy world.

Joe

Edit: Probably using the color sampler tool on the model's face.

 

[kanuski]

That's what I am talking about. I will look that up. Thanks.

 

[KmH]

Hover the cursor over the area you want to check. Look at the RGB values listed just under the lower left edge of the histogram.

Caucasian skin highlights are exposed just about right when between 235 and 240 in the red channel, assuming the color has been corrected.

SmugMug | How to get pleasing skin tone

 

[kanuski]

Ok, that helps even more. Thanks.
So I try this and get an R value of 28-30ish. What am I missing?

 

[KmH]

My bad. I forgot. Lightroom can't do what I do when I use Camera Raw and CS 5.
Though LR and Camera Raw both use ACR there are some differences.

Lightroom also doesn't do CMYK, so the link I posted will only be helpful if you have Elements or Photoshop.

You might find something here - Check portrait exposure using Lighroom - Bing

 

[hirejn]

There's an old trick called using a light meter that when used correctly renders every tone under the light accurately. If you have to check exposure in post, that's a little late.

 

[Ysarex]

Ok, that helps even more. Thanks.
So I try this and get an R value of 28-30ish. What am I missing?

You're missing a lot. I called this idea a fauxtographer's fantasy for good reason. If you believe you can do this then I have an incredible real estate deal in south central Florida I want to talk to you about.

First, are you loading raw files into LR or camera JPEGs? If camera JPEGs then your original exposures have already been manipulated by the camera software. If raw files then LR is manipulating your original exposures in real time right in front of you.

Before you use the color sampler tool make sure and set the default curve to linear. That way you'll at least be "supposedly" removing LR's bias from the interpretation of your exposure -- only you really can't pull out that bias as it's fundamentally engineered in.

In other words you can't use LR to check camera exposure because LR manipulates what you see and screws with the exposure and there's no way for you to disengage this behavior in LR. Let's do an example. Here's a section of the same photo opened in two different raw converters:



LR is on the top. You can see the color sampler marker in the middle of the forehead of the gentleman with his arms outspread. The values are R=192, G=170, B=142. Before taking that measurement I set the cuve to linear and the only other adjustment made was to white balance the photo. So the question is do those values have any real direct unmanipulated relationship to the camera exposure? And the answer is no.

The bottom version of the the Photo is from Capture One 7. Again I set the default curve to linear and I white balanced the photo. Capture One has the same ability to do a color sample and so I sampled the exact same spot on that fellow's forehead. The values are R=140, G=117, B=90. I could have a slight sampling error but not a discrepancy like that. Since Capture One costs 3 times as much as LR it must be right and LR must be wrong -- that's as good an argument as any. It's not really a case of one or the other being right or wrong. Whoever told you that you could do what you're suggesting doesn't understand how this type of software works.

If you want to use post software to examine your camera exposures and evaluate those exposure after the fact you need an entirely different product: RawDigger: Raw Image Analyzer | RawDigger

Joe