79 lines
2.9 KiB
ReStructuredText
79 lines
2.9 KiB
ReStructuredText
Terminology
|
|
===========
|
|
|
|
.. image:: images/strike.gif
|
|
:width: 128
|
|
:alt: strike
|
|
|
|
The following definitions are used throughout this documentation.
|
|
They are consistent with the terminology used in the TIFF 6.0 specification.
|
|
|
|
Sample:
|
|
The unit of information stored in an image; often called a
|
|
channel elsewhere. Sample values are numbers, usually unsigned
|
|
integers, but possibly in some other format if the SampleFormat
|
|
tag is specified in a TIFF
|
|
|
|
Pixel:
|
|
A collection of one or more samples that go together.
|
|
|
|
Row:
|
|
An Nx1 rectangular collection of pixels.
|
|
|
|
Tile:
|
|
An NxM rectangular organization of data (or pixels).
|
|
|
|
Strip:
|
|
A tile whose width is the full image width.
|
|
|
|
Compression:
|
|
A scheme by which pixel or sample data are stored in
|
|
an encoded form, specifically with the intent of reducing the
|
|
storage cost.
|
|
|
|
Codec:
|
|
Software that implements the decoding and encoding algorithms
|
|
of a compression scheme.
|
|
|
|
.. _ImageFileDirectory:
|
|
|
|
Image File Directory (IFD):
|
|
An Image File Directory - in short also *directory* -
|
|
contains information about the image,
|
|
as well as pointers (offsets) to the actual image data
|
|
within the on-disk file.
|
|
An IFD points either to the next IFD or shows with a ''0''
|
|
that it is the last IFD in the IFD-chain.
|
|
|
|
Multi Images per TIFF file:
|
|
There may be more than one IFD in a TIFF file.
|
|
Each IFD defines a *subfile*.
|
|
One potential use of *subfiles* is to describe related images,
|
|
such as the pages of a facsimile transmission.
|
|
Such files are also named "*multi-page* TIFF" or "*multi-image* TIFF".
|
|
Refer also to :doc:`/multi_page`.
|
|
|
|
.. _SubFile:
|
|
|
|
Subfile:
|
|
*Subfile* is a term in the TIFF 6.0 specification for
|
|
an image and its associated *Image File Directory (IFD)*
|
|
in a TIFF file containing one or more images.
|
|
|
|
In order to better understand how TIFF works (and consequently this
|
|
software) it is important to recognize the distinction between the
|
|
physical organization of image data as it is stored in a TIFF and how
|
|
the data is interpreted and manipulated as pixels in an image. TIFF
|
|
supports a wide variety of storage and data compression schemes that
|
|
can be used to optimize retrieval time and/or minimize storage space.
|
|
These on-disk formats are independent of the image characteristics; it
|
|
is the responsibility of the TIFF reader to process the on-disk storage
|
|
into an in-memory format suitable for an application. Furthermore, it
|
|
is the responsibility of the application to properly interpret the
|
|
visual characteristics of the image data. TIFF defines a framework for
|
|
specifying the on-disk storage format and image characteristics with
|
|
few restrictions. This permits significant complexity that can be
|
|
daunting. Good applications that handle TIFF work by handling as wide
|
|
a range of storage formats as possible, while constraining the
|
|
acceptable image characteristics to those that make sense for the
|
|
application.
|