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Author Topic: Are digital intermediates uncompressed? Lyle Romer Phenomenal Film Handler Posts: 1400 From: Davie, FL, USA Registered: May 2002 posted 05-23-2006 08:56 AM                     The subject says it all. If so, 4K Digital Intermediates must be HUGE files.  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 05-23-2006 10:19 AM                     Are you distinguishing between lossy compression and lossless compression? For sure they are stored with some amount of lossless compression, but I can't imagine we would care... --jhawk  |  IP: Logged Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 05-24-2006 11:49 PM                     Apparently they are not compressed as compression would just slow down processing, disk space is cheaper than processor time. Scanning and film recording take considerable time, so only a few minutes of film should need to be online at any time - there are a lot of very large disk arrays involved though. After film recording the data is saved on tape until the project is complete, after that it can be archived (if someone wants to pay for the tapes) or discarded. Once a project is complete, there isn't much use for the data; film is a much more reliable storage medium than any magnetic one yet devised. You already have the camera negative and the final output film, the digital data is just representing them.  |  IP: Logged Aaron Haney Master Film Handler Posts: 265 From: Cupertino, CA, USA Registered: Jan 2001 posted 05-25-2006 01:19 AM                     EFilm says a 4K digital intermediate is 50 megabytes per frame. (EFilm was recently responsible for the 4K DI for "The Da Vinci Code", see here.) They are probably stored in some uncompressed high dynamic range format like Cineon or OpenEXR, although I wouldn't be surprised if a company like EFilm had their own format. Like Dave said, it is doubtful there is even any lossless compression involved, except perhaps for offline archives, as the time to compress / decompress every time you touch the data on disk would likely just slow down the workflow. Certainly there would be no lossy compression going on, as that would severely impact quality.  |  IP: Logged Tao Yue Expert Film Handler Posts: 209 From: Princeton, NJ Registered: Apr 2001 posted 05-27-2006 01:51 PM                        OpenEXR supports various compression methods (all lossless), see page 10 of: http://www.openexr.com/TechnicalIntroduction.pdf Hard to say whether it's faster to store it uncompressed on disk. Memory bandwidth is greater than bus bandwidth is greater than hard drive transfer rate. If a fast compression method (RLE) is used with a fast multi-core processor, it may come out a wash. You'd have to try it to see -- there are other limitations that don't necesssarily show up when you compare raw bandwidth of the various components.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 05-27-2006 02:57 PM                        quote: Aaron Haney EFilm says a 4K digital intermediate is 50 megabytes per frame. So what again does 4K refer to? 4K is a value....of what?  |  IP: Logged Mike Schindler Phenomenal Film Handler Posts: 1039 From: Oak Park, IL, USA Registered: Jun 2002 posted 05-27-2006 03:06 PM                     quote: Frank Angel So what again does 4K refer to? 4K is a value....of what? Lines of vertical resolution  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 05-27-2006 03:34 PM                        Then it should be so indicated....imagine if we did that with everything: 24 1K 30M 16 instead of 24fps 1KHz 30M ohms 16FtL So how about for digital projection: 4Klvr  |  IP: Logged Bobby Henderson "Ask me about Trajan." Posts: 10973 From: Lawton, OK, USA Registered: Apr 2001 posted 05-27-2006 03:45 PM                     A "4K" image can actually be in any number of different frame sizes. The only consistent value making it "4K" is the horizontal axis of the frame, measuring 4096 pixels. A 1.33:1 frame would measure 4096 X 3072 pixels. 8-bit color (per color channel): 36MB, 16-bit color (per color channel): 72MB. A 1.85:1 frame would measure 4096 X 2214 pixels. 8-bit color: 25.9MB, 16-bit color: 51.9MB A 2.39:1 frame would measure 4096 X 1714 pixels. 8-bit color: 20.1MB, 16-bit color: 40.2MB Note: these files sizes are for RGB color mode. Most lossless image file formats (everything from Photoshop and TIFF images to specialized formats like Scitex and Cineon) can use compression systems like LZW to cut file sizes roughly in half without permanently throwing away any data. You can get better levels of compression if the image is graphical in nature and has large areas of flat, identical color. The newest implementations of LZW use some of the same tricks utilized by the GIF format.  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 05-29-2006 08:34 AM                     For clarity, Mike and Bobby said two different things. I believe Mike is incorrect when he answers Frank, "4K is a value....of what?"; "Lines of vertical resolution " It is 4K pixels per line. Frank, it's a sad reality that people use the term "4K" a lot, so it's come into our speech without more clear units. But please don't make up a new abbreviation -- that will just engender lots of confusion (especially if it's wrong ). Bobby went on to say, "The newest implementations of LZW use some of the same tricks utilized by the GIF format." Err, LZW is the compression format used by GIF. This doesn't make a lot of sense, seeing as GIF's compression hasn't changed since 1989 (or 1987, depending on how you look at it). --jhawk  |  IP: Logged Mike Schindler Phenomenal Film Handler Posts: 1039 From: Oak Park, IL, USA Registered: Jun 2002 posted 05-29-2006 09:25 PM                     jhawk, If it's 4K pixels per line, then would it not also be 4K lines of vertical resolution? If anything, it seems like lines of vertical resolution is more informative, because it describes in what direction there are 4K pixels per line.  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 05-29-2006 09:39 PM                     4K pixels in each horizontal line. This is why the number stays constant across aspect ratios -- because the height of the image changes, but the width (4k) stays the same. --jhawk  |  IP: Logged Mike Schindler Phenomenal Film Handler Posts: 1039 From: Oak Park, IL, USA Registered: Jun 2002 posted 05-30-2006 09:42 AM                     Exactly. 4K Pixels Per Horizontal Line= 4K Lines of Vertical Resolution  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 05-30-2006 09:54 AM                     It is clear to me that "lines of vertical resolution" is not unambiguous. Evidently when you say it, you mean "there are 4k lines, each of them vertical." But my interpretation of the phrase is "there are 4k lines, and those lines define the vertical resolution, i.e. as you travel in the vertical direction you cross 4k of them." In my view, "vertical resolution" is a measure of how much precision there is in the vertical space, i.e. how many pixels high it is. Perhaps you see it differently, but I recommend adopting phrasing that is unambiguous. --jhawk  |  IP: Logged Bobby Henderson "Ask me about Trajan." Posts: 10973 From: Lawton, OK, USA Registered: Apr 2001 posted 05-30-2006 03:23 PM                     I wish those folks would do like professional graphics people do when describing a raster-based image: give the full image dimensions in pixel numbers on both X and Y axis. 4096 X 2214 X RGB 8/24 or RGB16/48 means a lot more to me than some stupidly vague term like "4K". Honestly, "4K" is merely a term for laypeople to use. It communicates very little in professional terms.  |  IP: Logged

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