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Atom Types in QuickTime Image Files

There are two mandatory atom types: 'idsc', which contains an image description, and 'idat', which contains the image data. This is illustrated in Figure A-1. A QuickTime image file can also contain other atoms. For example, it can contain single-fork preview atoms.

In QuickTime 4, there is a new optional atom type 'iicc', which can store a ColorSync profile.

Figure A-1 shows an example QuickTime image file containing a JPEG-compressed image.


Figure A-1  An 'idsc' atom followed by an 'idat' atom

An 'idsc' atom followed by an 'idat' atom

Table A-1  A QuickTime image file containing JPEG-compressed data

0000005E

Atom size, 94 bytes

69647363

Atom type, 'idsc'

00000056

Image description size, 86 bytes

6A706567

Compressor identifier, 'jpeg'

00000000

Reserved, set to 0

0000

Reserved, set to 0

0000

Reserved, set to 0

00000000

Major and minor version of this data, 0 if not applicable

6170706C

Vendor who compressed this data, 'appl'

00000000

Temporal quality, 0 (no temporal compression)

00000200

Spatial quality, codecNormalQuality

0140

Image width, 320

00F0

Image height, 240

00480000

Horizontal resolution, 72 dpi

00480000

Vertical resolution, 72 dpi

00003C57

Data size, 15447 bytes (use 0 if unknown)

0001

Frame count, 1

0C 50 68 6F 74 6F 20 2D20

4A 50 45 47 00 00 00

00 00 00 00 00 00 00 00

00 00 00 00 00 00 00 00

Compressor name, "Photo - JPEG" (32-byte Pascal string)

0018

Image bit depth, 24

FFFF

Color lookup table ID, -1 (none)

00003C5F

Atom size, 15455 bytes

69646174

Atom type, 'idat'

FF D8 FF E0 00 10 4A 46

49 46 00 01 01 01 00 48

...

JPEG compressed data

Important:  The exact order and size of atoms is not guaranteed to match the example in Figure A-1. Applications reading QuickTime image files should always use the atom size to traverse the file and ignore atoms of unrecognized types.

Note: Like QuickTime movie files, QuickTime image files are big-endian. However, image data is typically stored in the same byte order as specified by the particular compression format.



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Last updated: 2007-09-04

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