28-29
Checksum of header (XOR of bytes 0-27). If Checksum is FFFF
then ignore it.
It is assumed that either the Metafile or the TIFF position and length fields
are zero. That is, only one or the other of these two formats is included in the
EPS file.
The Metafile must follow the guidelines the Windows specification sets forth.
It should not set the
viewport
or
mapping mode,
and it should set the
window
origin
and
extent.
The application including the EPS file should scale the pic-
ture to fit within the
%%BoundingBox:
comment specified in the EPS file.
6
Device-Independent Screen Preview
This screen preview format is designed to allow EPS files to be used as an
interchange format among widely varied systems. The preview section of the
file is a bitmap represented as ASCII hexadecimal to be simple and easily
transportable. This format is called encapsulated PostScript interchange for-
mat, or EPSI.
An EPSI file is truly portable and requires no special code for decompressing
or otherwise understanding the bitmap portion, other than the ability to
understand hexadecimal notation.
The
%%BeginPreview:
width height depth lines
and
%%EndPreview
com-
ments bracket the preview section of an EPSI file. The
width
and
height
fields
provide the number of image samples (pixels) for the preview. The
depth
field provides the number of bits of data used to establish one sample pixel of
the preview—typical values are 1, 2, 4, 8. An image that is 100 pixels wide
will always have 100 in the
width
field, although the number of bytes of hexa-
decimal needed to build that line will vary if
depth
varies. The
lines
field tells
how many lines of hexadecimal are contained in the preview, so an applica-
tion that does not care may easily skip them. All arguments are integers.
The bit order of the preview image data is the same as the bit order used by
the
image
operator. That is, the preview image is considered to exist in its
own coordinate system. The rectangular boundary of the preview image has
its lower-left corner at (0,0) and its upper-right corner at (
width
,
height
). The
byte order is fixed and should be (0,0) through (
width –
1), then (0,1) through
(
width –
1,1), etc.
24
(1 May 92)