CHAPTER 4
334
Graphics
should not reference the PostScript definitions corresponding to PDF procedure
sets (see Section 10.1, “Procedure Sets”), which are subject to change.
4.8 Images
PDF’s painting operators include general facilities for dealing with sampled im-
ages. A
sampled image
(or just
image
for short) is a rectangular array of
sample
values,
each representing a color. The image may approximate the appearance of
some natural scene obtained through an input scanner or a video camera, or it
may be generated synthetically.
FIGURE 4.25
Typical sampled image
An image is defined by a sequence of samples obtained by scanning the image
array in row or column order. Each sample in the array consists of as many color
components as are needed for the color space in which they are specified—for
example, one component for
DeviceGray
, three for
DeviceRGB
, four for
DeviceCMYK
, or whatever number is required by a particular
DeviceN
space.
Each component is a 1-, 2-, 4-, 8-, or (in PDF 1.5) 16-bit integer, permitting the
representation of 2, 4, 16, 256, or (in PDF 1.5) 65536 distinct values for each com-
ponent. (Other component sizes can be accommodated when a
JPXDecode
filter
is used; see Section 3.3.8, “JPXDecode Filter.)