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Author Topic: Lightroom color temperature  (Read 3886 times)
Robert Spoecker
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« on: October 09, 2006, 02:30:48 PM »
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I am shooting with a Canon 5D. I just shot a few images of a volunteer with two photofloods with 3200 degree color temperature lights. I have a Wibal card in one of the pictures. When I process the image in Lightroom the automatic white balance selector eyedropper clicked on the Wibal card produces very bad colors. When I adjust the color temperature with the slider at 3200 it still will not give good results.

When I used the  Digital Photo Professional that came with the camera the eyedropper technique produces good results.

Anyone else experience this? Or better yet, can anyone think of what I may be doing wrong if anything?

I love lightroom because it supports raw images from both the 5D and my Leica Digilux 2 and I do not want to upgrade to photoshop CS2. I have CS.

Robert
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Robert Spoecker
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« Reply #1 on: October 09, 2006, 06:23:13 PM »
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Well, by playing with Lightroom I discovered that my Wibal card white was completly blown, that is 0,0,0 for the r,g,b colors. That would account for all this I suspect. When I clicked the eyedropper on the black sticker that comes with the Wibal the colors all turn out good. I will never understand all of this (arrrgg) but as long as I can make it work I am a happy camper.

Maybe I should delve into this stuff longer before bothering the forum with this.    

Robert
« Last Edit: October 09, 2006, 06:24:37 PM by Robert Spoecker » Logged
hdegroot
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« Reply #2 on: August 09, 2007, 10:31:30 AM »
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Robert,

White balance is a much more complicated topic then it seems on the surface.  The deeper you go, the more confused it is possible to get.  

One of the things I try to keep in mind with white balance is that the raw image converter needs a neutral reference in order to eliminate color casts in your photograph due to the temperature of the illuminant light.  I don't think it matters  whether you use a white object, a light gray object, or the Digital Grey kard (http://hTtp://www.digitalimageflow.com) which my company makes.  (but see below)

It is interesting that Photoshop Lightroom allows the user to adjust the color temperature into a JPEG file.  I actually don't understand exactly how this is accomplished in the software and I need to find out more.  Perhaps one of the users of this forum can comment on this interesting feature of Lightroom.

The really  important feature is that the object you do use spectrally neutral. A truly neutral white balance reference, or gray card, acts as a color temperature mirror, and it faithfully reflects the true nature of the light that falls on it back into the camera's digital sensor, without adding, subtracting, or altering the light in any way.

It's helpful to use a gray surface rather than a white surface, because the white surface can be blown out, which in technical terms means that the image sensor will have exceeded its maximum brightness value in that particular area.  A gray card will not blow out.

In achieving white balance, what we are achieving its color constancy.  This is a way of saying that the color of objects appear the way we expect them to appear across a wide range of illuminant light sources. Human eye and brain is used to seeing objects remain constant in color, and we perform a mental white balancing on things we see in order to maintain color constancy of objects in our environment.

When lit by light of varying color temperature, the light reflected off an object will actually be quite different and it normally would appear different to our eyes, just as it should.  However, the brain performs a sophisticated type of white balancing in order to maintain color constancy.  This makes it easier to recognize familiar objects in our environment.  Imagine if you went to look for your car in the parking lot and the color was radically different in every garage depending on the light! I suspect you'd end up walking home a lot!  This is why color constancy is important to the human brain, and why color constancy is important in digital photographs.

I recommend my white balance product - the Digital Grey Kard - as a simple, economical, and highly accurate solution for your white balance problems.
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digitaldog
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« Reply #3 on: August 09, 2007, 11:53:23 AM »
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Sounds like you're shooting Raw so you need to first understand that Raw data is essentially Grayscale, there's no color. YOU produce color and tone based on the rendering controls in either converter you're using.

2nd. The WB in camera plays no role in the WB you can or may produce in the converter. Its simply a suggestion.

3rd. Unless you actually measure the color temp using the right instrument (a Spectrophotometer), keep in mind that defining color using the Kelvin scale is pretty inaccurate. Lots of different colors correleate to the same color temperature. We also don't know under the hood how each converter is calculating this (the processing color space and other factors will play a role).

Bottom line is, you may assume the lights are putting out a correlated color temperature of 3200K when they may not. Setting a converter to WB at 3200 isn't necessarily going to produce the desired rendering. So don't worry, make the image appears as you wish.

You DO want to white balance on a white (not gray) for Raw. Something close to the 2nd lighter patch on a Macbeth Color Checker. Not a specular white but a white if possible due to the gamma encoding of Raw data (half of all the data is within the first stop of highlights. See: http://www.luminous-landscape.com/tutorial...se-right.shtml)

When you say your Whitebal card was totally blown out, was that before or after adjusting the Exposure slider? Go right ahead and tone that done to see if indeed you really DID over exposed as defined in the above article. The default setting for exposure doesn't at all mean you've blown out the highlight data in the Raw, only the current rendering settings. Now if you crank Exposure down all the way and you still get 255 (100%), you did over expose past the point of sensor saturation. There's no data there.
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Andrew Rodney
Author “Color Management for Photographers”
http://digitaldog.net/
Mark D Segal
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« Reply #4 on: August 09, 2007, 07:24:12 PM »
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Andrew,

A couple of points to add to this:

If Robert's Lightroom settings for Brightness and Contrast are above zero, or his quick develop settings in the Library Tab are too high, this could also given an impression of much brighter or more blown-out data than actually "procured" from the camera.

Secondly, I've been advised that the white balancing aspect of the Camera Raw profiles for individual camera models is based on that second grey patch (beside the white) in the GM ColorChecker card.

Mark
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml
digitaldog
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« Reply #5 on: August 09, 2007, 07:34:35 PM »
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Probably because Thomas builds his profiles using the Macbeth 24 patch target.
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Andrew Rodney
Author “Color Management for Photographers”
http://digitaldog.net/
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