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[[File:HEIF and ISO base media file.png|centre|thumb|HEIF and ISO Base Media File|642x642px]]
Files conforming to ISOBMFF consist of a sequence of data structures called boxes, each containing a four-character code (4CC) indicating the type of the box, the size of the box in terms of bytes, and the payload of the box. Boxes may be nested, i.e. a box may contain other boxes. ISOBMFF and HEIF specify constraints on the allowed box order and hierarchy.
=== Image Items ===
The roles of image items as specified in HEIF are listed and described below. Note that a single image can be associated with more than one role.
{| class="MsoNormalTable"
|
'''Role'''
|
'''Description'''
|-
|
coded image
|
A coded representation of an
image.
|-
|
derived image
|
An image that is represented in a file by an indicated
operation to indicated input images and can be obtained by performing the
operation to the input images. See also section '''Error!
Reference source not found.'''.
|-
|
cover image
(a.k.a. primary item)
|
A representative image of the
image items and image sequence tracks of the file. The cover image should be
displayed when no other information is available on the preference to display
the image items of the file. The file can have only one cover image.
|-
|
thumbnail image
|
A smaller-resolution
representation of a master image. A master image can have multiple thumbnail
images (e.g. different resolutions).
|-
|
auxiliary image
|
An image that complements a master
image. For example, an alpha plane or a depth map. Can assist in displaying
the master image but is not typically displayed as such.
|-
|
master image
|
An image that is not a thumbnail
image or an auxiliary image. It typically represents a full-resolution displayable image.
|-
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hidden image
|
An image that should never be
displayed. Can be present in the file for example as an input image for a
derived image.
|-
|
pre-derived coded image
|
A coded image that has been
derived from other images. For example, a high dynamic range image derived
from an exposure-bracketed set of images. The input images used for
derivation are linked to the final pre-derived coded image by referencing. No
derivation operation is defined.
|}
== References ==
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