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Old Feb 2, 2007, 2:16 PM   #1
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Using an RGB vs a luminosity histogram

I have read about how to use a RGB histogram although I am still confused.

  • How do you compensate for a blown or clipped color channel? [/*]
  • Is on color channel more important than another?[/*]
  • Do you expose to the right?[/*]
  • Which is more useful and why?
[/*]
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Old Feb 2, 2007, 3:31 PM   #2
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I'm not sure if I'm completely understanding the question. I can view a histogram on my images when I preview them, and then there's histograms within Photoshop, but I'm wondering if you're talking about some more advanced camera feature I've never used?

As far as in Photoshop, I don't think there's much practical difference between the two. The RGB would probably be a bit more accurate because luminosity is usually a B&W interpretation of the RGB image, which usually isn't an even mix of all 3 channels.

Part of the reason for that is the answer to your second question, which is that the green channel is given some priority because it captures twice as much detail as the other two channels. If you take an image at a higher ISO you can really see the difference by viewing the image data on the individual channels.

For the rest of your questions, I'm not sure how to answer them because I'm not sure I really understand where your questions are coming from. I'd suggest that the RGB would be more useful if you can view the individual channels because that can be a useful indicator of temperature and tint, and whether your white balance is looking good. Otherwise, I'm not sure how helpful I am to you.
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Old Feb 2, 2007, 4:23 PM   #3
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I'm sorry, the camera RGB histogram.

Like the Nikon D40 or the Canon Xti.
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Old Feb 2, 2007, 4:41 PM   #4
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RGB histogram will give a better indication of exposure when there is a strong primary color or lack of one in the photo. Example would be a brightly lit yellow flower. There will be little or no blue in the highlights, and you may need to stop down a bit to keep from blowing the red and green channels. The RGB histogram will show this, where the luminance histo may not.

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Old Feb 2, 2007, 4:53 PM   #5
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jbarrick wrote:
Quote:
I'm sorry, the camera RGB histogram.

Like the Nikon D40 or the Canon Xti.
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Yeah, the color histogram is better. I have the D50 and I wish it has split-color historgram. But I've learned to understand a scene, and can tell when a channel is probably blown, even though the histogram doesn't indicate it.

The other part of your question, I do "expose to the right". I still need to understand what you're trying to shoot. If it's a sunset or a dark animal, then I expose it to be darker. All "expose to the right" means is that you don't underexpose in purpose, for no reason. I followed the "under-expose" rule initially but found that exposing to the right results in better images.

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Old Feb 2, 2007, 5:29 PM   #6
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Expose to the right:


http://www.luminous-landscape.com/tu...se-right.shtml
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