Monday 21 August 2006

Film and DPI

How many dpi is 35mm movie film?

A film maker friend asked for stills scanned from his 35mm original movie film frames. For publicity. And the agency wanted 300 dpi. My million-dollar Spirit scanner does 4k. So it scans a 35mm frame in a size 2048x1556 or 4096x3112. So how many dpi is that?

I set about thinking. First off, dpi is dots per inch. It is a measure for printed material. As in printed on paper. Inkjet printers do 600 or more dpi. So whether you hold the printout an inch from your nose ot at arm's length there's still 600 dots in one inch. But film? How many dpi?

When working in Photoshop one often encounters a figure of 72 dpi for TV. That is arrived at by assuming a 14" TV set. Such a set shows a picture about 13" diagonal. Which by using Pythagoras gives you about 10.6 by 8 in. For a PAL 720x576 picture that's about 72 dpi. So TV is 72 dpi for a 14" TV set. For a 20" set it is 48 dpi and a 29" TV shows just 33 dpi.

So basically for non-print images dpi is not fixed, but varies by the size of the medium. So how about film? Better than 72 dpi? Can we get some 300 dpi please?

Here's my take and I may not be entirely correct. Here goes anyway...

35mm film scanners for movie production scan at 2048x1556 pixels (at 2k) or 4096x3112 pixels (at 4k). At 2k (2048x1556) a standard 35mm frame of 18x24 mm is about 2200 dpi on the film. At 4096x3112 you've got about 4400 dpi. Impressive, but noone watches film on film. They watch it projected on a screen in a theatre.

In a theatre the same 35mm frame gets blown up to a giant screen of, say, 20 feet across. Now since the number of pixels remain unchanged you have a picture 2048 pixels by 1556 pixels. At 20 feet across, that's just over 8 dpi. Even a scan of 4096x3112 (4k) yields only 17 dpi. Appalling!

But hey, you watch that screen from 50 feet away. So you're not going to see it as 8 dpi. Its like they print magazines at 300 dpi, but the same ads in a magazine are printed on hoardings not at 300 dpi, but much less, like 10 dpi or something.

So dpi is a measure for fixed size printed matter. Which can be viewed at varying distances even very close. But film and TV are not fixed and can be viewed in various sizes and distances. But never too close. So dpi doesn't apply to film at all.

Monday 14 August 2006

16mm vs HD for DI

Hardly a week passes when a prospective producer/director/DP calls and gets into a discussion on HD as a medium for film shooting. Resolutions, latitudes, sharpness, examples, dos and donts follow and the discussion always ends with the usual - "Sure its like film but..."

I spend a lot of time looking at digital film images. I work with a post setup in Mumbai which is the only one of its kind that has a 'near-2k' (soon to be full 4k) digital cinema projector. And this projector Is not your standard 'Powerpoint' projector, but a high resolution, Cinema-quality projector.
The point is, if you aren't looking at theatrical release bound images in a theatrical environment, you're always going to be surprised when it goes out to film eventually.

While debating the merits and demerits of shooting HD for theatrical release, many fall for the hard-sell of compressed 1280x720 HD formats. And some dabble with the latest compressed 1080 interlaced HDV.

But I have still to meet someone who even considers 1080p HD uncompressed - the only format that truly approaches film. But even 1080p uncompressed comes nowhere close to the sheer joy of a true 35 mm picture shot with a prime lens. Well graded and put out to 35mm. Nothing at all.

Sadly enough, budgets needed to film and finish in 35mm film are getting harder to find. And with 'let's do DI' mantra, nearly any of the benefits of shooting 35 are harder to sell. So HD seems extremely attractive alternative to 35mm flim.

Wait a minute. How about 16mm? It's film after all. The camera is small and quiet and doesn't need the complicated setup of HD cameras. Most DOPs are comfortable with the basic methodology of shooting 16 so they can concentrate on crafting great-looking shots instead of wading through menus and sub-menus looking for a setting to change something. Or fiddle with tiny controls and do colour tweaks that are easier to achieve in post. And while shooting HD, without a good calibrated monitor on set you just can't judge how your blacks are going to really look (and this is NOT racial).

And if you're doing DI scanning 16mm at 2k is as good as scanning 35mm at 4k. Yes sure, think about it. If your scanner - Spirit4k or Arriscan - scans the entire 16mm image area at 2k, its going to resolve as much detail as a 4k scan would see in a 35mm image area.

16mm stock is also cheaper by a third. 400 foot magazines run 11 mins so you're good to go for long scenes and multiple takes. Especially in songs.

Earlier this year, Arri introduced a new 16mm camera. The Arriflex 416. I've seen the 416 at an exhibition. Seems like everything a cinematographer would want in a movie camera. It does super16 so a naturally 16:9 frame aspect. Arri has done a great job of describing the camera as well as pointing out benefits in a digital world so I won't repeat it. Just head over to...

http://www.arri.com/entry/416.htm

So the pros of shooting 16mm over not shooting film at all would be...
1. Small light cable-free camera.
2. Easy to use, imager (stock) well understood.
3. Clean sharp optical viewfinder.
4. High resolution nearly indestructive original (film, lasts a century)
5. Future progress in conversion can yield better results. HD will never increase latitude/resolution regardless of future processing.
6. Stock (film) less volatile than tape, Cannot be erased.
7. Gorgeous high resolution exhibition master (film print, in film projector, in theatre), as opposed to small screen TV viewing or unpredictable video projection.

And the pros of doing HD would be...
1. Video tape, instant gratification. No processing.
2. Economical stock, so "keep rolling", and "let's do another take" possible incessantly.
3. Interview based or extempore performances can be accomodated.
4. With good on set monitor, exact post-shoot look can be visualized.
5. On-set adjustments possible with near-post like creative possibilities.
6. Sound and picture on same stock means less hassles in post.
7. Multi-camera shooting feasible so shoot time can be optimized.
8. Medium is digital anyway so integrating with graphic elements better.

Bottom line... think for yourself, your project and its needs. 35mm and HD don't even compare. But 16mm and HD make film thinkable as an option. And even if you still select HD you don't need to feel bad as long as you don't go near compressed tape formats. In that case please do 16mm.