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- Path: sparky!uunet!ogicse!uwm.edu!linac!uchinews!uchinews!a-giles
- From: a-giles@uchicago.edu (Aaron Giles)
- Newsgroups: comp.sys.mac.programmer
- Subject: Re: QuickTime and Fast Dithering
- Message-ID: <A-GILES.92Nov5092453@opal1.uchicago.edu>
- Date: 5 Nov 92 15:24:53 GMT
- Article-I.D.: opal1.A-GILES.92Nov5092453
- References: <40577@sdcc12.ucsd.edu>
- Sender: news@uchinews.uchicago.edu (News System)
- Reply-To: a-giles@uchicago.edu
- Followup-To: comp.sys.mac.programmer
- Organization: University of Chicago High Energy Physics
- Lines: 36
- In-Reply-To: sakelley@euclid.ucsd.edu's message of 5 Nov 92 01:26:34 GMT
-
-
- Scott> Here's the problem I'm having: by default, QuickTime is
- Scott> displaying everything using it's "fast dither" algorithm. This
- Scott> is fine for video clips, but for still images (JPEG), we'd
- Scott> like to do a little better. According to the QT 1.0
- Scott> developer's guide, page 3-20:
-
- Scott> "Apple decompressors use fast dithering when copying from
- Scott> image band buffers to 8-bit destinations. If the accuracy for
- Scott> decompression is above normal, then the decompressors use true
- Scott> error diffusion rather than fast dithering."
-
- Scott> Does this imply that QT will ALWAYS use fast dithering to an
- Scott> 8-bit destination, or is it possible to bump up the "accuracy"
- Scott> setting for playback to get better results? If so, how can I
- Scott> set this accuracy setting?
-
- (Note that I don't have the docs with me, so the exact names I specify
- may be wrong, but this should give you the general idea.)
-
- You can bump up this accuracy by passing codecHighQuality for the
- accuracy parameter in the FDecompressImage() call. If you're drawing
- PICT files, you'll need to set up a StdPix bottleneck and call
- GetCompressedPixMapInfo() on the PixMap you're passed to get all the
- parameters you need for the FDecompressImage() call. Then just call
- FDecompressImage(), manually setting the accuracy to codecHighQuality
- or something greater (codecMaxQuality should work as well).
-
- Note that you can also *suppress* dithering of compressed PICT files
- in this way, by forcing the dither flag on or off. This is the only
- way to suppress dithering in QT1.0. QT1.5 supports an extension of
- the ditherFlag in DrawTrimmedPicture(), which essentially does just
- what I've explained, only internally.
-
- Aaron
- a-giles@uchicago.edu
-