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Thread: Understanding the Histogram - Dark Scene example

  1. #1
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    Default Understanding the Histogram - Dark Scene example

    I've been asked by a couple of people to explain what the histogram is. I'm deliberately trying to keep this simple to help newer photographers. No doubt there are better explanations on the web but hopefully this will be helpful to some.

    Basically the Histogram is a graph with a horizontal and vertical axis. This graph shows a breakdown of viewable tonal range within an image.

    The Horizontal axis (left to right) is a tonal scale from BLACK (on the far LEFT), through MID TONE GREY (in the middle) and WHITE (on the far RIGHT).

    The Vertical axis shows the amount of information relating to a particular tone along the Horizontal axis.

    Understanding the histogram is important in creating a well exposed image. If you were to photograph a Grey Card (a simple card which is mid-tone/18% grey) the histogram should show a tall spike right in the middle of the graph. If the spike was on the far left of the histogram then the image would be underexposed. If that spike was on the far right of the histogram then it would be overexposed.
    It then becomes more complicated with an image with alot of different tones and this is where its important to understand. The most important thing is to not have lots of information right at the extremes of the graph -eg: if it is too under/overexposed there isn't any information recorded in the visible spectrum by the cameras sensor and you will have either "blocked up blacks" or "blown highlights".

    Below is an image that is predominately dark/black. A very dark bird against an even darker background.
    You can see that the majority of the information is to the left of the mid point. At first glance you might think this means it is underexposed, but by understanding that it is a black bird you realise that this is where it should be to gain detail in the dark areas without trying to make the black bird white (or too overexposed). The other thing to note is that if you were to expose this any more, you would start to blow out the highlight areas on the bill/face. Something that is a bit hard to see in this example is that there is a thin line of information stretching from the base of the dark grey spike right up to the white point. This thin line is the small amount of information/tone which includes the face,bill,eye etc.

    If you were using EVALUATIVE METERING, the camera would try to shift that solid mass of tonality into the middle as it wants to average the exposure to MID TONE GREY. It would therefore become OVEREXPOSED. So in this instance (DARK BIRD AGAINST A DARK BACKGROUND) the exposure was probably around -2/3 stop UNDER the metered exposure.

    Hope that helps anyway Feel free to comment or add to this.
    Click image for larger version. 

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    Cheers, Dave

    www.davidstowe.com.au WORKSHOPS

    Aus Life List IOC= 684 - Grey Honeyeater
    "So God created every winged bird according to its kind. And God saw that it was good." Genesis 1:21


  2. The following 3 users say thank you to David Stowe for their reply:

    Adam Blyth (30-09-2011), Mark Young (12-10-2011), Ray Walker (29-09-2011)

  3. #2
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    That's very informative Dave. I can follow that..thanks...
    The voices in my head may not be real, but they come up with some great ideas..

    Cheers Rev.

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    Thanks Dave, very informative.
    Aus list 632 (Powerful Owl, Callala Bay, NSW, 01-05-2014, finally thanks Matt!)
    Year list 159 (Powerful Owl, Callala Bay, NSW, 01-05-2014)

  5. #4
    Tony Hansford Guest

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    So if I was shooting a seagull on a typical Qld sandy beach, then the histogram would be pushed up the right end? And that would be a good exposure? And I shouldn't try to force it back to the left side or to the middle?

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    Thats right Tony but it will most likely be up to you to push the histogram to the right. Below is a shot like you mentioned with a bright white gull on a fairly bright sandy beach. You can see that the histogram is mostly bunched up on the right due to the bright tones but I actually added +1 stop of exposure compensation (CW metered) to get it there. If it was up to the cameras meter it would have tried to underexpose it and you would be seeing a histogram that was mostly centralised in the graph.


    Click image for larger version. 

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  7. The following 2 users say thank you to Paul Randall for their reply:

    Andrew Bonnitcha (22-10-2011)

  8. #6
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    Quote Originally Posted by Tony Hansford View Post
    So if I was shooting a seagull on a typical Qld sandy beach, then the histogram would be pushed up the right end? And that would be a good exposure? And I shouldn't try to force it back to the left side or to the middle?
    Yes Spot on Tony
    A great example from Paul too.
    Cheers, Dave

    www.davidstowe.com.au WORKSHOPS

    Aus Life List IOC= 684 - Grey Honeyeater
    "So God created every winged bird according to its kind. And God saw that it was good." Genesis 1:21


  9. The following user says thank you to David Stowe for their reply:


  10. #7
    Tony Hansford Guest

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    I appreciate the help you guys offer me. I know this is not just for my benefit but I appreciate it.

  11. #8
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    Quote Originally Posted by Tony Hansford View Post
    I appreciate the help you guys offer me. I know this is not just for my benefit but I appreciate it.
    Thanks Tony! Your post means alot to us too. Our aim for this forum is for it to be a friendly and helpful community where we look out for each other. Perhaps doesn't always work out exactly right but it's what i love about Feathers & Photos.
    Cheers, Dave

    www.davidstowe.com.au WORKSHOPS

    Aus Life List IOC= 684 - Grey Honeyeater
    "So God created every winged bird according to its kind. And God saw that it was good." Genesis 1:21


  12. #9
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    i am also VERY appreciative of the efforts you guys are going to, to explain the dark arts of digital photography! I am reading all these threads 'how to' intensly, .. CHEERS GUYS!

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