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D70 - Histogram - what am I looking at? - Photography

OK, so I've rtfm'd, and have an idea of the basics, but any tips on the histogram? I gather horizontal axis is brightness and vertical is nr of pixels. (Not actually described in the manual). I suppose you want the 'centroid' to be reasonably centred, and fairly well spread but with not too much area in the left or right tails. Any good primers? I also gather that the n highlight display lets me see what parts of the pic are clipped, and I have a few options: - knock exposure down manually and "burn"/"dodge" in an off-line prog - ...

  1. #1

    Default D70 - Histogram - what am I looking at?


    OK, so I've rtfm'd, and have an idea of the basics, but any tips on
    the histogram? I gather horizontal axis is brightness and vertical
    is nr of pixels. (Not actually described in the manual). I suppose
    you want the 'centroid' to be reasonably centred, and fairly well
    spread but with not too much area in the left or right tails.
    Any good primers?

    I also gather that the n highlight display lets me see what
    parts of the pic are clipped, and I have a few options:

    - knock exposure down manually and "burn"/"dodge" in an off-line prog
    - reduce contrast in image optimisation (JPG)
    - switch to NEF, where I'll have more bits to recover detail by
    doing manual adjustments later off-line

    Is that basically right? What am I missing?

    --
    Ken Tough
    Ken Guest

  2. #2

    Default Re: D70 - Histogram - what am I looking at?

    "Ken Tough" <co.uk> wrote in message
    news:co.uk... 
    -------------------
    There is a good description of the histogram here:
    http://luminous-landscape.com/

    Use the pull down menu found on the "Understanding Series" button.

    The only thing noteworthy (other than the tutorial), I found, is that
    each camera may assign a preference to one of the RGB channels in the
    histogram display.
    You can verify this by looking at the histograms for each channel separately
    in PS.
    It is possible to have a "normal" looking histogram with saturation present
    in one of the channels.

    Regards,
    Don F



    Don Guest

  3. #3

    Default Re: D70 - Histogram - what am I looking at?

    Ken Tough wrote:
     

    If your scene is mainly white, you would want the histogram to show up mostly to
    the right. If your scene is mainly dark, your histogram would be mostly to the
    left. It's a histogram, not an exposure meter. If you see, for example that it
    is likely that there is more information 'rightwards' of the historgram then
    likely you over exposed... If there is a lot of blank space between the histo
    and the right side, and you know there are white elements in the scene ... you
    underexposed.

     

    RAW (perhaps NEF) to conserve maximum information for post edit. If you see
    that areas of scene clipped high, then you must reduce the exposure to conserve
    detail. If the clipped areas are minor, or deliberately there (lights, some
    reflections), then leave them.

    Experiment.


    --
    -- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
    -- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
    -- [SI] gallery & rulz: http://www.pbase.com/shootin
    -- e-meil: there's no such thing as a FreeLunch.
    Alan Guest

  4. #4

    Default Re: D70 - Histogram - what am I looking at?

    "I found, is that each camera may assign a preference to one of the RGB
    channels in the histogram display."

    Would looking at a histogram help you determine if you have your white
    levels set correctly?

    Aldo Guest

  5. #5

    Default Re: D70 - Histogram - what am I looking at?

    Aldo Pignotti wrote:
     

    I don't think so. The histogram shows how much 'lightness' there is in the
    image and are mostly an aid to placing the exposure properly.

    White levels go to the color temp of the light source.



    --
    -- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
    -- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
    -- [SI] gallery & rulz: http://www.pbase.com/shootin
    -- e-meil: there's no such thing as a FreeLunch.
    Alan Guest

  6. #6

    Default Re: D70 - Histogram - what am I looking at?

    My understanding is that the only real reason to examine the histogram
    is to see if shaddows are clipped (moving off the top left). I shoot
    with the highlights screen & darken if there is any flashing burnt
    highlights. Further adjustments can then be done in photoshop. If the
    shadows are clipped a second shot to overlay/merge might be needed in
    extreme cases.

    If shooting jpeg that makes sense to see if a contrast adjustment was
    needed to spread it out or tighten it up.
    paul Guest

  7. #7

    Default Re: D70 - Histogram - what am I looking at?

    On Tue, 25 Jan 2005 12:27:09 +0200, Ken Tough <co.uk> wrote:
     

    The histogram shows you the range of pixel numbers verses brightness, but it may
    be useless data!

    For example, a night shot is going to be mostly dark, and a snow scene mostly
    white, so the histogram will look skewed, but so what?

    What you really want to see in the histogram is whether or not there are 'clear'
    areas at one or both ends. If there are, it is an indication that you can change
    the exposure to take advantage of this range. However, you may find that an
    increased range is not necessarily a good picture! Lots of times I've adjusted a
    portrait to get full range only to find its made the face too contrasting.
    Sometimes limited range is good!

    For an other example, if you take a snow scene and see that there are no pixels
    at the dark end, you can drop the exposure down and maybe get more detail in the
    snow. However, if you see in the next histogram that there is a 'bulge' that
    looks clipped off at that end, then you know you went too far, and you have
    pixels lost in the black.

    It's a bit of hard work using the histogram to take picture exposure info,
    because it changes for each picture. But if you really want to maximize your
    range, you can shoot a series of bracketed pics and watch the histogram to get
    an idea of where you are.

    My main use of the histogram is to see if I have any unused space in the
    exposure that I can use. Sometimes an automatic expose reading will be a bit
    wrong, and you will see it right away by a lack of pixels at one end. It's now
    easy to dial in some compensation to use the missing range.

    I also find it easier to adj on a 19" monitor rather then in a 1" camera screen!
     

    Bob Guest

  8. #8

    Default Re: D70 - Histogram - what am I looking at?

    The PS Camera Raw Plug-in (CRP) has an RGB histogram and so does
    BreezeBrowser which is sort of interesting, that that I necessarily know
    what to do with that either... but the cool thing about the CRP is that
    you can adjust exposure compensation, brighness, contrast & shadows and
    of course WB & watch what that does to the histogram as you tinker.

    Hold down alt while sliding exposure or shadows & it shows the areas
    being clipped (not apparent on the histogram). The brightness & contrast
    dials supposedly don't have this risk of clipping but I noticed
    increasing contrast sometimes drops the hump on the histogram so it
    looks pretty wimpy. Maybe that's OK too, it just means the highs & lows
    are more balanced & less middle tones. It is a funny contradiction
    though that a bold high contrast image has a flat looking histogram.

    The histogram can also be watched while adjusting all these to see if
    parts extend off the top and to expand the image to fill unused left &
    right areas though that's not always desireable.

    Such complicated interesting stuff!
    paul Guest

  9. #9

    Default Re: D70 - Histogram - what am I looking at?

    Don F <com> wrote:
     
    ....

    Thanks for this, and for all the other helpful replies.

    --
    Ken Tough
    Ken Guest

  10. #10

    Default Re: D70 - Histogram - what am I looking at?

    paul <net> wrote:
     

    True, it seems counter-intuitive at first glance. Thinking about
    that, though, will give me a nice feel as to how 'contrasty' the
    image is. It doesn't seem nice to lose contrast range just to
    keep a few highlights in though. I suppose that's where your own
    custom non-linear contrast map could come in useful (one I left off
    my list of potential fixes). Who knows, I might get around to that
    one day, but as yet I'm not even printing much.

    --
    Ken Tough
    Ken Guest

  11. #11

    Default Re: D70 - Histogram - what am I looking at?

    Ken Tough wrote:
     

    Are you talking about loading a custom curve into the camera? That might
    be helpful if you didn't want to shoot RAW. AFAIK it's only possible to
    load one curve though it would be nice to have a low contrast curve for
    bright sky situations, etc.

    I've come to the conclusion that I really need to bracket for those
    bright sky shots & merge the two. I had really bad results shooting the
    other day trying to underexpose to save highlights my shots were
    terribly underexposed, even with RAW I could not recover them
    acceptably. For the amount of work involved to do all that it might well
    be wise to load a custom curve instead.
    paul Guest

  12. #12

    Default Re: D70 - Histogram - what am I looking at?

    paul <net> wrote:
     [/ref]
     

    Yeah, exactly. That's what I was thinking of.
     

    The page DonF recommended (http://luminous-landscape.com/) has
    mention of the merging for high-contrast situations. I would
    love to see the impact of such a curve, since I have been a
    bit disappointed at trying to take dramatic sky shots along
    with landscape.

    --
    Ken Tough
    Ken Guest

  13. #13

    Default Re: D70 - Histogram - what am I looking at?

    Ken Tough wrote:
     [/ref]
    >

    >
    >
    > Yeah, exactly. That's what I was thinking of.
    >

    >
    >
    > The page DonF recommended (http://luminous-landscape.com/) has
    > mention of the merging for high-contrast situations. I would
    > love to see the impact of such a curve, since I have been a
    > bit disappointed at trying to take dramatic sky shots along
    > with landscape.
    >[/ref]
    Check out Photomatx.

    Jan
    Jan Guest

  14. #14

    Default Re: D70 - Histogram - what am I looking at?

    Jan wrote: 
    >>
    >>
    >> 
    >>
    >>
    >>
    >> Yeah, exactly. That's what I was thinking of.
    >>
    >> 
    >>
    >>
    >>
    >> The page DonF recommended (http://luminous-landscape.com/) has
    >> mention of the merging for high-contrast situations. I would
    >> love to see the impact of such a curve, since I have been a
    >> bit disappointed at trying to take dramatic sky shots along
    >> with landscape.
    >>[/ref]
    > Check out Photomatx.[/ref]


    Hmmm... http://www.hdrsoft.com/

    " Saving time in post-processing
    Photomatix Pro is designed for productivity -- automatic blending,
    unlimited stacking, easy comparison of results and batch processing save
    hours of masking and layers work in image editing softwares."
    paul Guest

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