Understanding this Histogram - Red, Blue, Green

Discussion in 'Photo Assignments & Technical Challenges' started by NancyMoranG, Nov 22, 2015.

  1. NancyMoranG

    NancyMoranG Been spending a lot of time on here!

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    Hi,
    took the photo in Raw on a D7000. These birds came up from behind, and I shot directly over my head as they went over me. ( Yes, exposure is off)
    When taking photo from the 'grid' in PSE 11 into the 'Editior" my Camera Raw program kicks in for adjustments first.
    I know that histograms show me dark to the left, bright to the right and I should look for even through the histogram.
    But this is just 3 colors, obviously telling me its too much. But to just have the 3 colors is adding to my confusion on histograms.
    Can you explain in terms a non-techie can understand .....
    Thanks. Pelican Histogram.JPG


     
  2. Ysarex

    Ysarex Been spending a lot of time on here!

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    ACR shows you 3 histograms simultaneously overlaid together. You see a red channel, green channel, and blue channel histogram together. Where the histograms overlap you see the color produced by the two or three channels mixed. So if you see yellow you're seeing where the red and green channels overlap. If you see magenta you're seeing where the blue and red channels are overlapping. Where you see white you're seeing the overlap of all three channels.

    Joe
     
  3. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    Sky shots and birds in flight are one of those situations where you will often get a histogram just like the one you have posted when you look at the RGB histogram. It's perfectly normal.

    There is another histogram display which is the luminescence histogram which is slightly different and shows a single block of data rather than 3 combined. In general terms the RGB and luminescence will be similar ; however it is possible to "clip" ergo overexpose a colour channel whilst not overexposing the luminescence histogram - far as I'm aware the reverse is not possible (or very rare).

    As such I typically have the camera set to show the RGB as its often very easy to clip a channel (esp the red channel).

    With the histogram you're showing its saying that you've got your 3 primary colours making up your photo; but that there is still a fair chunk of exposure space for you to use. Metering for sky shots often involves over-exposing from the meter reading as the sky is quite bright and acts just like snow in that the meter gets fooled and then tries to expose it as grey instead of the colour/brightness it really is.
     
  4. KmH

    KmH In memoriam Supporting Member

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  5. GHK

    GHK TPF Noob!

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    Could you post the image itself rather than a screen shot?
    GHK
     
  6. KmH

    KmH In memoriam Supporting Member

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    Raw files can't be posted on the internet.

    The photo would have to be opened outside Camera Raw after being assigned a file type of TIFF, JPEG, PNG, etc, then saved using a color space and bit depth amenable to posting on the Internet.
     
  7. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    Well the RAW file can't be shown as a photo on the internet, but there are many online downloading services that would let a person host the file online. Also for something like the histogram a simple jpeg of the original photo would suffice for a general understanding of it.
     
  8. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    Your blues are brighter than your greens, and both of them are brighter than your reds.
     
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  9. GHK

    GHK TPF Noob!

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    Yes, I do know this; I had just assumed that the post, being for the net, was a JPEG.
    GHK
     
  10. weepete

    weepete TPF Supporters Supporting Member

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    As has been mentioned the RGB historgam just shows you the values in each channel. I use it exactly like I would use the luminance one to check that none of the channels are clipped, if they are I adjust my exposure until they don't clip.
     

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