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HDCam DI


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#1 abadseed2

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Posted 15 August 2005 - 03:32 PM

I have just shot my short film on Super16 and I am looking into different post routes that are available. What seems to me to be the highest quality route that I can afford is to do a low contrast technical grade to HDcam, edit the film and then do a carefull grade and finish on a HDcam master with a possibility of later doing a 35mm print.

My questions are about the technical grade.

I've read somewhere that it is possible to do a transfer in log space, thus preserving more of the negative's dynamic range. Is this true and what are the consequence to the rest of the post process?

How good is a low contrast linear transfer? Will I be able to retrieve an acceptable amount of detail and colour information? Is this a better options then doing a best light transfer or an attended grade (given that I would be able to afford a limited time in the telecine)

And lastly do you think it is better to finish on 25fps or a 24fps master, given that I would like to eventually do a 35mm print, but that the video version will be more important in the beggining.

Many thanks for any thoughts.

Aleks
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#2 David Mullen ASC

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Posted 15 August 2005 - 05:14 PM

A "log" transfer is sort of similar to a flat "low con" transfer. You'd want to work with a DI place familiar with this, because you'd want your downconversions for editing, or an HD copy for editing, that goes through a LUT (Look-Up Table) to apply the right contrast for viewing on a monitor rather than spend months cutting this milky image.

You'd eventually make a color-corrected version with the log look for the film-out (which gets a LUT applied designed for film), and then make a separate HD master that had a LUT applied for all video versions (and digital projection.)

HDCAM is a rather compressed HD tape format with 3:1:1 color subsampling; you'd be better off transferring and mastering in HDCAM-SR (4:4:4) and if not, HD-D5 (4:2:2). Using HDCAM as the basis for a D.I. (which "City of God" did) adds a slight video-ish look to the image. As the tape formats improve, this problem gets better generally.

I assume you are only mentioning 25 fps because you are in a PAL/SECAM 50hz country... doesn't really matter for a film-out (24 fps versus 25 fps). It mainly is a sound issue more than a picture issue.
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#3 abadseed2

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Posted 16 August 2005 - 06:31 AM

Thanks David. I know that its better to transfer to SR or D5, but I have access to a XPri with a HDcam deck for free and I cant afford to work with SR and D5.
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#4 Adam Frisch FSF

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Posted 17 August 2005 - 07:42 AM

I'd take a look at Bonolabs telecine-to-hard drives that they do in HD. There's a link on the side here, somewhere. That way you get uncompressed HD, don't need any expensive tape based systems AND save money.
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#5 parallax

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Posted 18 August 2005 - 01:00 AM

A "log" transfer is sort of similar to a flat "low con" transfer.  You'd want to work with a DI place familiar with this, because you'd want your downconversions for editing, or an HD copy for editing, that goes through a LUT (Look-Up Table) to apply the right contrast for viewing on a monitor rather than spend months cutting this milky image.

You'd eventually make a color-corrected version with the log look for the film-out (which gets a LUT applied designed for film), and then make a separate HD master that had a LUT applied for all video versions (and digital projection.)

HDCAM is a rather compressed HD tape format with 3:1:1 color subsampling; you'd be better off transferring and mastering in HDCAM-SR (4:4:4) and if not, HD-D5 (4:2:2). Using HDCAM as the basis for a D.I. (which "City of God" did) adds a slight video-ish look to the image. As the tape formats improve, this problem gets better generally.

I assume you are only mentioning 25 fps because you are in a PAL/SECAM 50hz country...  doesn't really matter for a film-out (24 fps versus 25 fps). It mainly is a sound issue more than a picture issue.

<{POST_SNAPBACK}>


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#6 parallax

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Posted 18 August 2005 - 01:11 AM

[quote name='David Mullen' date='Aug 15 2005, 03:14 PM']
A "log" transfer is sort of similar to a flat "low con" transfer. [QUOTE]

What is the difference between the log transfer and the flat transfer?
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#7 Phil Rhodes

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Posted 18 August 2005 - 07:39 AM

Hi,

Woah, hang on, we're mixing technical terminology with broad descriptions here.

Briefly, and only slightly incorrectly:

A "log image" generally refers to a computer file representing a film scan where the brightness information is stored as the natural logarithm of the observed intensity. This concentrates quantisation levels in regions of luminance where they're most useful, at the upper end of the scale representing highlights.

Or, to put it another way, a log image has its tone curve intentionally bent to ensure that highlights are smoothly represented.

If you view a log image without correction on a linear display device (almost all display devices are more or less linear after they've had some sort of correction applied, be that Adobe Gamma Loader or Truelight or whatever) it will tend to look flat and low-contrast, but that's because you aren't actually displaying it correctly. Get XNview (free for most platforms) and view the Kodak test DPX file (available from their site) on your computer monitor. XNview doesn't know about logarithmic data, and it therefore looks very flat and low-con. Find software that knows how to linearise it (I don't know of any that doesn't cost a lot of money; After Effects will do it I believe, not that I've ever had a need to) and you will get something much more approximately correct.

This is quite apart from what you might call a "flat transfer", which I take to mean a cautious grade designed to record as much of the negative information as possible for later manipulation, and which I'd prefer to call a "technical grade". It's possible to create a flat transfer and then record it as either log or linear data; we're talking here about the fundamental difference between the way the data in the file is laid out, and the characteristics of the image it represents.

For what it's worth, the apparent luma-resolution increase provided by a log image is so acute, it's a rule of thumb that a 10-bit log image is of more or less equal worth as a 16-bit linear one with over a third less storage and processing overhead.

Phil
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#8 John Pytlak RIP

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Posted 18 August 2005 - 10:07 AM

Kodak published and patented lots of good work on this as part of Cineon.

The Kodak Cinesite has some technical papers:

http://www.cinesite.com/?1632&0&
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