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Merging RGB monochrome captures?


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#1 Robert Szanto

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Posted 08 December 2010 - 05:23 PM

I've read that all the professional film scanners take up to 27 monochrome exposures of each frame in order to capture as much usable information as possible (three bracketed exposures per filtered color).

Would it be possible to recreate this process on my own with a monochrome industrial camera scanning the film directly off of a projector's gate (assuming the projector has a motor capable of frame by frame motion)?

Is there a way to batch merge all these images together (first an HDR merge and then an RGB channel merge)?
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#2 Phil Rhodes

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Posted 09 December 2010 - 06:52 PM

Yes; it's been done before. Google for info, I can't remember exactly where.

You can do the merging in a Photoshop batch file and end up with 16 bit TIFFs or something. It could probably also be done with a free tool like ImageMagick, which I suspect would be faster, but I'm not sure about the HDR operation.
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#3 Karel Bata

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Posted 10 December 2010 - 08:19 PM

Robert, am I reading your post correctly? Are you intending to extract HDR footage from traditionally shot film negative?

If so, you are wasting your time. I experimented with doing going this route a few years back and was getting progressively closer with good looking tests, but gave up when I saw the spec for the Alexa and knew that digital cameras would pretty soon be able to capture HDR footage in-camera. RED are currently talking about how their next generation will have some kind of HDR capabilty built in.

Doing it with film is attractive, but there are many problems. Are you planning to put neg stock in your projector..? How will you get the different exposures? You need to capture the images as RAW - any compression will show up later. And you're using a monochrome camera? How will you get back to color? Sounds like very long-winded process that will take many hours to yield a few seconds of results.

A lot of people are experimenting with HDR right now. Here's an interesting example using two REDs on a mirror rig, and then luma-keying the result later

And then of course there's all the post... :blink: Have you ever wondered why so many folk do an excellent HDR time-lapse, but then don't bother doing another..?

If you're on a Mac, check out Luminance. You'll have to set up a preset then batch process. Photomatix is excellent.

Be warned - Huge amounts of data, masses of overnight rendering. :D
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#4 Stuart Brereton

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Posted 10 December 2010 - 10:44 PM

Are you intending to extract HDR footage from traditionally shot film negative?



Film negative is already High Dynamic Range footage. ;)
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#5 Karel Bata

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Posted 11 December 2010 - 08:55 AM

Is that a gauntlet I see before me..?

Yes, of course film is HDR. However, without DI you don't get access to the full range available on the negative. Or rather you only get to print up or down and then you lose something at the other end (unless you go DI with all the expensive scanners and what-not, but I assume that here we're discussing the possibility of a cheaper route) I'll post an example (I hope Robert doesn't mind):

Posted Image Posted Image


The first is a regular scan off a neg. The second used three scans spaced at 2 stops which were tone mapped later.

I'll be the first to say that the tone-mapping here is clumsy and we've all seen better, but this was one of my first attempts and I don't have anything really good on this PC right here. But I think it demonstrates the principle.
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#6 Robert Szanto

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Posted 12 December 2010 - 03:24 PM

That's a perfect example of what I was referring to.

I completely forgot that the newest digital cameras are/will be HDR ready. This would definitely help bring down the time and file size it would take to do it with individual stills. The best solution would probably be to rent the camera for a day (probably not possible now, but once things settle down it might become an option), and then capture a 2k HDR frame by frame video of the film (probably using reversal stock since capturing off of a negative brings in all sorts of problems).

Thanks for the info!

Edited by Robert Szanto, 12 December 2010 - 03:27 PM.

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