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multiple passes at different exposures


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#1 thomas-english

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Posted 19 March 2006 - 05:34 PM

I am shooting some fashion vignettes next week on super8 and 200t . Going to TK at widescreens "Flashscan".

Have any of you had any success doing multiple passes brighter and dimmer than optimum and recombinding the image in after effects. For more detail from the highlights and dark bits?

Any hints of how much brighter and darker?

Any tricks on after effects?

thanks
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#2 David Cox

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Posted 19 March 2006 - 06:37 PM

It depends what you are trying to achieve. Remember that the limitation is the latitude of the video format you are transferring to, so if you?re after extending the detail across the whole image, all you will end up doing is reducing the contrast to fit more exposure detail into the video latitude. This could be done with a single pass.

Where you can get an advantage is if there are defined areas in your frame where different telecine ?exposure? settings can be combined. For example, a scene inside a room that has a window to the outside world in the background can be taken from one pass, while the scene outside the window can be taken from a darker pass so that you get detail inside and outside the room. In this case, you would matte one pass onto the other. Likewise for getting cloud detail back in skies.

If you were transferring in a full telecine suite, multiple grading windows now cover many requirements for multi-passes within the grading session. These are effectively soft edge shapes that place different grades on different parts of the image. I think the FlashScan device you are using is a simpler device that won?t have these features.

There is a problem you are very likely to face ? multiple passes can weave (wobble) differently. The smaller the film format, the greater the weave and the weave is most noticeable when you have two passes moving against each other. Most new telecine systems have electronic frame stabilisation in them, but it is very possible that when you get your multiple super-8 passes back and try to comp them, they will start moving against each other. This will mean they need stabilising, and After Effects stabilising does soften with image more than its more expensive counterparts.

So I suggest getting two test passes and see if they weave differently. If they don?t ? great! If they do, and stabilising doesn?t work well, you?ll either have to settle for a single pass or look for another alternative. Such alternatives might include finding a full telecine suite that is able to handle super 8, or transferring your film ?low contrast? to keep all the detail and re-grade in your After Effects or finding a service that can scan your super 8 to files with a greater latitude (greater bit depth) than video ? i.e. DPX or Cineon files. These will give you more information from the film in a single pass, that you can then matte together into the video latitude.

Not as simple as it should be, is it?!

david cox
Baraka Post Production Ltd
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#3 thomas-english

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Posted 20 March 2006 - 03:46 AM

Thanks David, your advice is most kind.

Your correct , the flashscan is clearly a very basic unit and will not have these features. Whilst experimenting on my first tests should I have my second pass as a brighter pass (shadow detail) or a darker pass (highlight detail) which would I see the most benifits from?

I am overexposing by 1/3rd of a stop. Possibly considering compressing the blacks on final grade if they are very noisy.
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#4 David Cox

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Posted 20 March 2006 - 04:42 AM

It does depend exactly what?s in your shot, and how "noisy" the Flashscan transfer is. I would probably suggest setting for the highlights, as these would otherwise be clipped off the video transfer and this is where you would loose detail. You might be able to restore some detail in the dark areas from this pass in later colour correcting, thus avoiding having to do two transfers if this process doesn?t bring up too much noise / grain.

Do some tests though. You might find that transferring two passes just gives you lots of headache for not much gain.
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