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- Path: sparky!uunet!gumby!wupost!waikato.ac.nz!ldo
- From: ldo@waikato.ac.nz (Lawrence D'Oliveiro, Waikato University)
- Newsgroups: comp.sys.mac.programmer
- Subject: Re: QuickTime and Fast Dithering
- Message-ID: <1992Nov6.151855.12011@waikato.ac.nz>
- Date: 6 Nov 92 15:18:54 +1300
- References: <40577@sdcc12.ucsd.edu>
- Followup-To: comp.sys.mac.programmer
- Organization: University of Waikato, Hamilton, New Zealand
- Lines: 87
-
- In article <40577@sdcc12.ucsd.edu>, sakelley@euclid.ucsd.edu (Scott Kelley) writes:
-
- > I'm doing a project in MacroMind Director that also uses QuickTime.
- > Since Director's built in support for QuickTime isn't sufficient for our
- > needs, I've beed writing XObjects (Director's version of XCMD's) to play
- > back movies and still images. We want to store stills and video clips at
- > 24-bit color and then have them "dither down nicely" for display on
- > 8-bit systems.
- >
- > Here's the problem I'm having: by default, QuickTime is displaying
- > everything using it's "fast dither" algorithm. This is fine for video
- > clips, but for still images (JPEG), we'd like to do a little better.
- > According to the QT 1.0 developer's guide, page 3-20:
- >
- > "Apple decompressors use fast dithering when copying from image band
- > buffers to 8-bit destinations. If the accuracy for decompression is
- > above normal, then the decompressors use true error diffusion rather
- > than fast dithering."
- >
- > Does this imply that QT will ALWAYS use fast dithering to an 8-bit
- > destination, or is it possible to bump up the "accuracy" setting for
- > playback to get better results? If so, how can I set this accuracy
- > setting? This setting is NOT the "temporal/spatial quality" setting;
- > I've tried setting those high and low and I always get the fast dither.
- > I have found a couple of functions in the movie toolbox (like
- > SetMediaQuality) and in the image compression manager
- > (SetDSequenceAccuracy) that seemed to imply (I hope) that I could
- > specify that I wanted high quality just before I started playback, and
- > that I would get what I want. But I haven't been able to sort out the
- > details well enough to actually try it yet.
-
- Hi, Scott!
-
- Now, you need to keep a number of different concepts straight here:
-
- * The spatial/temporal quality settings govern the amount of *compression*
- you get; as you rightly observed, they don't control whether the decompressors
- use fast dithering on playback or not.
- * The media quality setting (as set by SetMediaQuality) is nothing more than
- an informational hint to the Movie Toolbox; it allows you to have alternative
- versions of tracks that contain the same information at different quality
- levels (e g a video track optimized for 4-bit displays versus another one
- optimized for 8-bit displays), and have the Movie Toolbox automatically pick
- the right one based on your system configuration.
- * You're getting very warm with your comment about SetDSequenceAccuracy.
- When you decompress an image, you can specify an "accuracy" setting, which
- specifies how much effort the decompressor should put into the job. You
- can specify a range of numeric values, but all that really happens in
- practice is that, if you specify a value of "normal", then you will get
- fast dithering (if appropriate), whereas if you specify a value greater than
- this, the image will be drawn using standard QuickDraw drawing modes,
- including normal QuickDraw dithering if appropriate.
-
- Unfortunately, the playback decompression sequence is buried in the depths of
- the workings of the video media handler, and I know of no calls to let you get
- access to it.
-
- > I should also probably point out that right now I'm working with JPEG
- > images stored as single-frame movies. This is because Director's native
- > support for QuickTime only recognizes MooV files, so to get it to load a
- > JPEG image, I have to store it as a movie. I could store the JPEG images
- > as compressed PICT images and then use Director's "link to file" option
- > for PICT's, but that doesn't work for us because it stores absolute
- > pathname links. Eventually we will move to using all our own XObjects to
- > talk to QuickTime, and, if necessary, I can write a separate XObject
- > for stills.
-
- I'd say you're really better off abandoning the single-frame movie approach,
- and storing your stills as (JPEG-compressed) PICTs. And if Director is too
- inflexible with its links to files, then to hell with it--write that stills
- XObject!
-
- One of my current projects is a simple interactive tour, with lots of still
- images stored as JPEG-compressed PICT files. I'm doing it in HyperCard, with
- a whole lot of custom XCMDs and XFCNs. I'm actually storing aliases to the
- individual picture files, which gives you a bit more flexibility in how you
- arrange things.
-
- I think Director is a marvellous tool for creating animations, but I personally
- prefer to put together final presentations in HyperCard. It's sort of like
- plasticine: some may see it as a kids' toy, but I can mould it into any shape
- I want!
-
- Lawrence D'Oliveiro fone: +64-7-856-2889
- Computer Services Dept fax: +64-7-838-4066
- University of Waikato electric mail: ldo@waikato.ac.nz
- Hamilton, New Zealand 37^ 47' 26" S, 175^ 19' 7" E, GMT+13:00
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