Digital equivalent of Push/Pull exposure ?

Discussion in 'Digital Photography' started by holydiver, Aug 29, 2003.

  1. holydiver

    holydiver Guest

    Hi,
    Is there a digital equivalent of push/pull exposure ?
    Can it be done in camera, or in post processing from converting from
    RAW to tiff ?
    thanks
     
    holydiver, Aug 29, 2003
    #1
    1. Advertisements

  2. holydiver

    Tom Nelson Guest

    The simplest simulation of a "push" is to increase the ISO of the
    camera.

    After exposure, you can simulate a film push very successfully in
    Photoshop. Use Levels or preferably Curves and drag the end point on
    the white side sideways toward the dark side (this will make more sense
    when you see it). You are increasing the contrast of the image,
    increasing visible detail of all tones, and bringing your greyed-down
    whites closer to white.

    You can decrease contrast (similar to a "pull") with Curves by dragging
    the endpoints up and down, or by dragging a midpoint up or down. The
    more horizontal the curve is, the less the contrast. Notice that, if
    you're dragging a midpoint, you are simultaneously increasing contrast
    for some tones and decreasing it for others. This is usually a Good
    Thing.

    You can't rescue blown-out highlights as you can by pull-processing,
    but you can do a lot to save almost-whites. In Photoshop, copy the
    background layer and set the copy's blending mode to Multiply.

    Tom Nelson
    Tom Nelson Photography
     
    Tom Nelson, Aug 29, 2003
    #2
    1. Advertisements

  3. Sure! Almost all cameras have the ability to use several ISO values ,
    usually 100,200, and 400. But some go as low as 50 and as high as 1600.
    As with film, the higher the digital ISO, the greater the "noise"
    (equivalent to grain in film).
    Push/Pull can also be performed on your computer with a any photo
    editing software.
    In digital jargon it's called adjusting levels.
    Bob Williams
     
    Robert E. Williams, Aug 29, 2003
    #3
  4. holydiver

    Bert Hyman Guest

    (Robert E. Williams) wrote in
    But does it really work?

    With real film, pushing is effectively underexposing and then
    overdeveloping to retrieve more info from the latent image.

    With a digital exposure, there's no "hidden" info in the bits that
    can be retrieved with post processing.

    So, what's really going on?
     
    Bert Hyman, Aug 29, 2003
    #4
  5. Yes; that's what turning up the ISO above 100 is doing (push).
     
    David Dyer-Bennet, Aug 29, 2003
    #5
  6. holydiver

    Bert Hyman Guest

    (Alan F Cross) wrote in
    I see... My A60 doesn't do RAW, so I've never been moved to find out
    just what that was all about. Maybe it's time to look it up :).
     
    Bert Hyman, Aug 29, 2003
    #6
  7. holydiver

    Andrew Guest

    With a raw image there is hidden info that's not present in the jpeg
    version. Many cameras output raw iamges with 10, 12 or 14 bits of
    resolution per color, but downsample to 8 bits if you select jpeg
    as the output format. I've had excellent results correcting underexposed
    pictures.

    Andrew
     
    Andrew, Aug 29, 2003
    #7
  8. Bert Hyman wrote in message ...
    [..]
    You are not actually pushing anything. The gain in shadows is form nil
    to very little, whereas better exposed parts of the image gain a good
    deal. In other word, one develops to get a somewhat printable image. A
    significant amount of noise (=visible grain) comes with it.
    Says who? Very small charges are retrievable - with varying results
    from a pictorial point of view.

    As with film, it is always possible to try to change the signal-to-noise
    ratio. A digital camera such as Nikon D100 will tweak its sensitivity
    to 6400 ISO (BTW, Nikon does not say it's 6400 ISO, the call it "High"
    or something similar), and the image has an awful amount of noise. You
    may of course additionally set the EV compensation to -2 - you will
    definitely be able (sometimes) to see what the camera has recorded.
    Exposing any B&W film to such an equivalent ISO rating (6400 * 2) would
    not give you much of an image, regardless of the amount of pushing in
    development.

    In astro photography it is common practice (with digital cameras)) to
    expose up to hundreds of shots of the same stellar or planetary image,
    and then literally add them together with appropriate software.
    Individually, these shots are worthless. Whether this is (physically)
    similar to retrieving a latent image, I don't know, what happens is that
    a set of very small charges are added up, to give a useful image.
    Whatever one may care to call it, the result is very similar to push
    processing.

    Regards,
    Carsten J. Arnholm, Oslo, Norway.
    http://carnholm.home.online.no
     
    Carsten J. Arnholm, Aug 29, 2003
    #8
  9. holydiver

    JPS Guest

    In message <biodp4$n5e$>,
    And it's not just more "in-between values" ... some RAW formats, like
    those used in the Canon DSLRs have an extra range of highlights in the
    RAW file that can be extracted with the proper tools. The RAW files
    from my 10D have about a stop of extra RGB highlights beyond what a JPG
    can convey, and more greyscale levels above that. By greyscale, I mean
    that at the highest channel levels, all three channels are exactly the
    same in the files I've examined.
    --
     
    JPS, Aug 30, 2003
    #9
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.