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Unit 4: Image
The problem with this—and there had to be one—is that IE6 does not support alpha channels. notes
Once a new version of IE comes out with this vital support, you should see the effect springing
up on trendy designers’ sites across the Web.
And what of animation? PNG can be made into multi-image files through the MNG extension of
the format, but browser support is patchy for this format. Stick with GIFs for your animations.
The GIF was the first image format to be used on the World Wide Web.
4.8 Macintosh image format
The Macintosh PICT (Macintosh Picture) format is associated with applications on the Macintosh
and is one of the best supported formats on that platform. The PICT files are meant to encapsulate
the functionality of QuickDraw, the native graphics drawing protocol on the Macintosh, and
consist mainly of QuickDraw calls arranged in no particular order. There have been two major
releases of QuickDraw, v1.0 and v2.0 (Colour QuickDraw). There have also been numerous minor
QuickDraw revisions, each associated with a corresponding Macintosh PICT version.
QuickDraw v1.0 supports monochrome bitmaps up to 32K in size. Image resolution is fixed at
the original Macintosh display resolution, or 72 dpi.
QuickDraw v2.0, sometimes known as Colour QuickDraw, supports 8-bit bitmaps as well as
monochrome. There is no compression available for 8-bit Version 2.0 PICT files.
All information in Macintosh PICT files is stored in the data fork of the Macintosh file pair.
Although the resource fork may be present, it is left empty. Image data is stored in binary format
and consists of a series of operators and associated data.
High-level routines in the Macintosh ToolKit are available to read and write PICT files and are
often used when writing applications that translate PICT files to other image file formats.
4.8.1 file organization
All Macintosh PICT files start with a 512-byte header, which contains information that the
Macintosh use to keep track of the file. This is followed by three fields describing the image size
(picSize), the image frame (picFrame), and a version number. In v2.0 files, another header follows.
In both versions, the preceding information is followed by the image data. In all versions, the end
of the file is signalled by an end-of-file operator.
4.8.2 file Details
QuickDraw, and consequently the Macintosh PICT format, is far too complex for us to do justice to
it here, so we will merely note some details about the start of the file. A good deal of information
and codes are included on the CD-ROM. Note that most secondary references only give examples
of bitmap encoding and ignore the vector nature of the format.
The information following the platform-specific 512-byte header is in the following format:
SHORT File size in bytes
SHORT Frame x-value of top left of image (at 72 dpi)
SHORT Frame y-value of top left of image (at 72 dpi)
SHORT Frame x-value of lower right of image (at 72 dpi)
SHORT Frame y-value of lower right of image (at 72 dpi)
in v1.0 files, this is followed by:
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