Digital 'Push processing'.

Discussion in 'Film and Processing' started by rodeo_joe|1, Jun 17, 2021.

  1. This is a follow up to a discussion started in another thread, and triggered by looking at the published curves of (chemically) push-processed film. From those curves it appears that push-processing reversal film buys you next to nothing in added shadow detail.

    At least, nothing that couldn't be got from alternative digital enhancement techniques.

    So I thought I'd post some pictures to illustrate.

    The following two shots were taken years ago on 50 ISO Fujichrome.

    The underexposed shot (bottom) was a genuine mistake, and got underexposed by about two stops before I reset the camera ISO to take the top picture.

    There's also quite strong lens vignetting that adds to the underexposure in the corners.
    Correct-Under-scans.jpg
    Both slides were copied in RAW format with a digital camera at the same 'scanning' exposure. I.e. the copying exposure was set just short of highlight-clipping for the correctly exposed slide and the same settings used for the underexposed slide. This gives an idea of how dark that slide appears to the eye.

    Next is the digitally 'pushed' version of the underexposed slide.
    Pushed-scan.jpg
    Extra camera-copying exposure was given, in addition to a tweak of the curves in Photoshop and a slight saturation boost. The aim was to try and match the shot exposed correctly in the camera. A pretty successful exercise, IMO.

    Here are 100% crops of the deepest shadow areas of the two slides.
    Shadow-details.jpg
    I don't see much shadow detail loss, apart from an increase in noise in the pushed version.

    In my view, the noise is actually less obtrusive than the increased grain and colour shift that you'd get from conventional push processing.

    Therefore it's my opinion that scanning and using digital enhancent techniques can make chemical 'pushing' a thing of the past. This is the 21st century after all.
     
    ajkocu and NHSN like this.
  2. I think you have it.

    I will just note that I have discovered empirically that old Kodachrome (especially) slides that seemed to have blacked out ("lost") shadow areas, often do respond to digital manipulation.

    This is the basis of the "O-zone Method" of course (LINK), but it's not "digital pushing' exactly.
     
    rodeo_joe|1 likes this.
  3. AKA, expose-to-the-right (ETTR) and fix the shadows in post. A technique that has become commonly used in digital shooting.

    However, with slide film the technique for deep shadow recovery isn't quite so simple. Since it usually requires an increase in scanning exposure, and most consumer film-scanners don't allow direct control of their exposure.

    But there's a sneaky fix for that: Some added exposure can be forced by the addition of an ND filter gel to the scanner's, usually open, calibration area. Depending on the scanner, you might be able to boost the physical exposure by a little over a stop with this kludge.

    Whereas digital camera copying of a slide is much more flexible in terms of exposure. Making a 2 or 3 stop boost no problem at all.

    This then usually reveals the 'parting of the ways' of the RGB density curves of the film in the deepest shadows, requiring their re-alignment by judicious use of the curves or levels tool in an image editor. Which is exactly what was done with my above example.

    So, not quite as straightfoward as lifting the shadows of a digital shot, but probably giving an overall better result than over-developing a film (and permanently crippling its tonal range in the process) just to gain a bit more brightness in the shadows and mid-tones. Because the true speed of the film isn't altered a jot by 'pushing' in that way.
     
  4. For slides you do not lose much shadow details if you underexposed. Only that you need a super bright projector to see the details. For color negative under exposed by 2 stop is really bad.
     

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