Speculation on the Cause of
the XL1 Banding/Posterization Problem:
a discussion thread by
Clif Anderson and Charlie Hand

The Watchdog notes: You may call up a Table of Contents for the DV to 35mm Guide using links at the top and bottom of the page for each article. It will appear in a separate window. All three parts of this document are available to download and print as a single Adobe Acrobat .PDF file or as a single MicroSoft Word 97 .DOC file. Many thanks to Chris Hauser of Tape House Digital Film in New York City for this contribution.

DV: Generic name for any of the 6.35mm digital videotape formats (DV, Mini-DV, DVCAM & DVCPRO). So long as a tape can play down in the THDF PAL DV deck, the trade names are immaterial. We can play the mini size with an adapter (just like VHS-C in a VHS deck) or the full size DV tapes. "DV" can be used to describe any of these formats since they all spawned from the same technology. Filmmakers submitting tape from cameras other than an XL1 or from a VTR should test for compatibility. Some cameras are not compatible in some decks. We’ll make a list as we go along.

Progressive Scan: There is some confusion over progressive scan video and the Canon Frame Movie Mode option on their 3 chip DV cameras. THDF has in the past wrongly assumed that Canon used Frame to describe a progressively scanned image. The engineers who designed the XL1 could not offer pixel shift (a feature that shifts the green CCD ½ a pixel from the red and green chip in order to increase sharpness, go to www.canondv.com for more info) and a true progressive scan in the same camera. They chose the sharpness advantage and found a workaround for a non-interlaced mode. Since the feature is not a true progressive scan, they had to call it something else. The way Frame Movie Mode duplicates the quality of a progressive scan chip is by taking field 2 of each video frame and interpolating a whole frame. They do this by comparing the two fields, making field two the dominate information and creating the missing lines (field one) in real time. The results are outstanding. We have yet to see any quantizing (that stairsteping, sawtooth, jagged edge uglies you get on diagonal edges) or motion artifacts on any of the Canon Frame Movie Mode footage we have shot to film. We have seen this on PAL interlaced video even after we’ve de-interlacing the footage.

In order to make 35mm from DV, filmmakers must shoot in either a Frame Movie Mode or a progressive scan at either PAL 25fps or High Definition 24fps. The onus is not on THDF to find out if cameras can shoot Frame Movie Mode or a progressive scan. Some cameras shoot in a still camera progressive mode. While it is true that this feature captures an image progressively, it is specifically for shooting one frame and holding it on tape for a few seconds. This is great for Digital C-Prints but wholly inappropriate for movies. A few cameras can shoot all three ways; interlaced, progressive/frame and still. If a filmmaker is not sure, they should submit a tape for evaluation. Make sure to have some horizontal motion in the footage so we can identify any interlacing. A point of interest (according to Panasonic) related to 625 PAL DV is that the "4:2:0 raster scheme has merits for progressively scanned images". This can only work in our favor in the DV to film transfer.

FireWire: Developed by Apple, a high-speed serial digital data bus, also known as IEEE 1394. For filmmaker’s purposes, FireWire allows DV cameras and editing computers a loss-less in/out. Except for testing, THDF has no practical use for FireWire in the transfer of DV to film. Filmmakers should only be submitting their conformed tape. Accepting only your tape eliminates the potential for problems in the camera to computer to tape link. It is the filmmaker’s responsibility to present a properly prepared tape for transfer.

Audio Stretch: A 25fps PAL tape transferred to 24fps film lasts 1 frame longer per second on film, 60 frames per minute and 3600 frames per hour. Said another way, 60 seconds of PAL lasts 62 ½ seconds on film. PAL on film runs 4.1666…% longer (25/24 = 1.041666…) Slowing the audio down to match the film is referred to by THDF as an audio stretch. We are encouraging filmmakers to stretch only the camera audio. With a full mix the process of slowing down audio to match the new length can be a very time consuming process. Each individual audio element has to be checked meticulously and tweaked in order to have it sound correct. If a 25fps final mix is brought in to be stretched, the mixer has to go through each element individually and re-build the final. It is best to perform a final mix with the camera audio stretched and the other elements at normal speed.

Canon XL1 (PAL version): A prosumer Mini-DV camera. The PAL version is about $1000 more than an NTSC. For purchases, there is a company in NYC that we are working with who imports them. I heard that Canon USA made an announcement at NAB 2000 that they will be selling and supporting PAL. The XL1 meets all our technical requirements namely PAL and Frame movie mode setting. The other features that should make filmmakers very happy are the interchangeable lens mount, XLR balanced microphone compatibility, full manual exposure and a FireWire in/out. The optional equipment available (not included in the base XL1 package) are a high resolution b/w viewfinder, full manual zoom lens (no servos), an auto/manual wide angle zoom, an adapter for Canon still camera lenses and an adapter for XLR microphones. The NTSC Canon GL1 meets our minimum requirements except that is a 30fps camera and it doesn’t accept professional audio (don’t worry, someone will make a widget for that real soon.) It costs less than an XL1. The PAL version of the GL1 is called the XM1. Updates to follow.

MAC G3/G4: Provided you order your computer correctly, the blue and white G3’s or the new G4’s out of the box are ready to go. A second hard drive is highly recommended. You don’t want to fragment the drive with the operating system. Also one hard drive can not read in two places at one time (DV and application program). An 18GB hard drive holds about 90 minutes of DV. Either an ATA/66 @ 7200 rpm or almost any of the SCSI drives are fast enough to read and write DV. Check with the software manufacturer before purchasing a FireWire hard drive. The transfer rate is borderline and you may drop frames. You should also have at least 128mb of ram. The video card and the two FireWire ports are fine as shipped from the factory. A small color video monitor is a great option. Filmmakers should have one for shooting anyway since focus and exposure are best judged with a monitor. You can view your editing with full screen full resolution playback when the camera is attached to the computer via the FireWire cable and the monitor patched to the camera’s RCA jacks.

Edit DV & Final Cut Pro: Editing software from Digital Origin & Apple that supports FireWire DV in/out with full support of the G3/G4 and XL1 platforms. The Edit DV Unplugged version is a stripped down low price option that should be fine for most editing. Digital Origin is one of the few software companies you can actually get on the phone (800#) for free technical assistance. Digital Origin used to go by Radius and had terrible customer service, but that is not the case now. We are not sure about Apple’s phone support. Both platforms have WWW users groups and there are even some books out there.

FireWire Cable: A six-foot cable can cost $50. No wonder it’s usually not included! You’ll need a 4 to 6 pin FireWire cable (normal peripherals need 6 to 6 pin). Cameras use their own power supply, so the 6 pin goes to the computer (2 for power, 4 for data) and the 4 pin in the camera (data only).

For more information contact Chris Hauser
TapeHouse Digital Film in New York City
tel. (212) 319-5084 cfh@tapehouse.com

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Thrown together by Chris Hurd