The base level of the VIPS I/O system provides IMAGE
descriptors.
An image represented by a descriptor may be an image file on disc, an area
of memory that has been allocated for the image, an output file, a delayed
computation, and so on. Programs need (usually) only know that they have
a descriptor, they do not see many of the details. Figure 3.1
shows the definition of the IMAGE
descriptor.
The first set of fields simply come from the image file header:
see §2.1 for a full description of all the fields. The next set
are maintained for you by the VIPS I/O system. Hist
is a pointer to
a string listing all of the operations which have been performed on this
image, see §3.3. filename
is the name of the file
that this image came from. If you have attached an eval callback to this
image, time
points to a set of timing statistics which can be used
by user-interfaces built on VIPS to provide feedback about the progress
of evaluation -- see §3.4. Finally, if you set kill
to non-zero, VIPS will block any pipelines which use this descriptor as an
intermediate. See §3.8.5.
The remaining fields are private and are used by VIPS for housekeeping.