GIF file format is complex and has different non-image data that can be stored before and after an image data. The GIF metadata design allows you to read/write any GIF non-image data and prevents from misunderstanding with GIF extensions storing order.
The following metadata are always saved before an image data:
- GIF Logical Screen Descriptor metadata level
- GIF Image Descriptor metadata level
- GIF Global Color Table metadata level
- GIF Local Color Table metadata level
All other GIF Extensions Metadata are saved before an image data.
ImageGear represents simpler GIF metadata by single metadata items, and more complex metadata by subtrees. Thus, there are two main GIF metadata levels in ImageGear:
- GIF Metadata Level
- GIF Extensions Metadata
This section provides information about the following:
GIF Metadata Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| GIF header level |
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| GIF Logical Screen Descriptor level |
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| GIF Image Descriptor level |
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| optional Global and/or Local Color Tables and |
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| optional GIF Extensions levels (extensions before image) |
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GIF Header Metadata GIF Metadata Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "GIFHeader" |
0x10 |
Tree |
0 |
NULL |
0 |
TRUE |
GIF Header Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "Signature" |
0x101 |
Leaf |
STRING |
"GIF" |
3 |
TRUE |
| "Version" |
0x102 |
Leaf |
STRING |
|
3 |
TRUE |
GIF Logical Screen Descriptor Metadata GIF Metadata Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "LogicalScreenDescriptor" |
0x20 |
Tree |
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GIF Logical Screen Descriptor Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "LogicalScreenWidth" |
0x201 |
Leaf |
UINT16 |
|
1 |
FALSE |
| "LogicalScreenHeight" |
0x202 |
Leaf |
UINT16 |
|
1 |
FALSE |
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| "Fields" |
0x205 |
Tree |
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| "GlobalColorTableFlag" |
0x206 |
Leaf |
BOOL |
|
1 |
FALSE |
| "ColorResolution" |
0x207 |
Leaf |
UINT8 |
|
1 |
FALSE |
| "SortFlag" |
0x208 |
Leaf |
BOOL |
|
1 |
FALSE |
| "GlobalColorTableSize" |
0x209 |
Leaf |
UINT8 |
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1 |
FALSE |
| "Fields" |
0x205 |
Tree |
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| "BackgroundColorIndex" |
0x203 |
Leaf |
UINT8 |
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FALSE |
| "PixelAspectRatio" |
0x204 |
Leaf |
UINT8 |
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FALSE |
GIF Global Color Table Metadata
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "GlobalColorTable" |
0x30 |
Leaf |
RAW_DATA |
|
Variable |
TRUE |
GIF Image Descriptor Metadata GIF Metadata Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "ImageDescriptor" |
0x2C |
Tree |
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GIF Image Descriptor Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "ImageLeftPosition" |
0x2C1 |
Leaf |
UINT16 |
|
1 |
FALSE |
| "ImageTopPosition" |
0x2C2 |
Leaf |
UINT16 |
|
1 |
FALSE |
| "ImageWidth" |
0x2C3 |
Leaf |
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1 |
FALSE |
| "ImageHeight" |
0x2C4 |
Leaf |
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1 |
FALSE |
| "Fields" |
0x2C5 |
Tree |
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GIF Image Descriptor Fields Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "LocalColorTableFlag" |
0x2C6 |
Leaf |
BOOL |
|
1 |
FALSE |
| "InterlaceFlag" |
0x2C7 |
Leaf |
BOOL |
|
1 |
FALSE |
| "SortFlag" |
0x2C8 |
Leaf |
BOOL |
|
1 |
FALSE |
| "LocalColorTableSize" |
0x2C9 |
Leaf |
UINT8 |
|
1 |
FALSE |
GIF Local Color Table Metadata
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "LocalColorTable" |
0x40 |
Leaf |
RAW_DATA |
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Variable |
TRUE |
GIF Extensions Metadata GIF Graphic Control Extension Metadata
GIF Metadata Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "GraphicControlExtension" |
0xF9 |
Tree |
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GIF Graphic Control Extension Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "Fields" |
0xF91 |
Tree |
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| "DisposalMethod" |
0xF92 |
Leaf |
UINT8 |
|
1 |
FALSE |
| "UserInputFlag" |
0xF93 |
Leaf |
BOOL |
|
1 |
FALSE |
| "TransparentColorFlag" |
0xF94 |
Leaf |
BOOL |
|
1 |
FALSE |
| "Fields" |
0xF91 |
Tree |
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| "DelayTime" |
0xF95 |
Leaf |
UINT16 |
|
1 |
FALSE |
| "TransparentColorIndex" |
0xF96 |
Leaf |
UINT8 |
|
1 |
FALSE |
GIF Comment Extension Metadata
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "CommentExtension" |
0xFE |
Leaf |
STRING |
|
Variable |
TRUE |
GIF Application Extension Metadata GIF Metadata Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "ApplicationExtension" |
0xFF |
Tree |
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GIF Application Extension Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "ApplicationIdentifier" |
0xFF1 |
Leaf |
STRING |
|
8 |
FALSE |
| "Appl.AuthenticationCode" |
0xFF2 |
Leaf |
UINT8 |
|
4 |
FALSE |
| "ApplicationData" |
0xFF3 |
Leaf |
RAW_DATA |
|
Variable |
FALSE |
GIF Plain Text Extension Metadata GIF Metadata Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "PlainTextExtension" |
0x01 |
Tree |
0 |
NULL |
0 |
TRUE |
GIF Plain Text Extension Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "TextGridLeftPosition" |
0x11 |
Leaf |
UINT16 |
|
1 |
FALSE |
| "TextGridTopPosition" |
0x12 |
Leaf |
UINT16 |
|
1 |
FALSE |
| "TextGridWidth" |
0x13 |
Leaf |
UINT16 |
|
1 |
FALSE |
| "TextGridHeight" |
0x14 |
Leaf |
UINT16 |
|
1 |
FALSE |
| "CharacterCellWidth" |
0x15 |
Leaf |
UINT8 |
|
1 |
FALSE |
| "CharacterCellHeight" |
0x16 |
Leaf |
UINT8 |
|
1 |
FALSE |
| "TextForegroundColorIndex" |
0x17 |
Leaf |
UINT8 |
|
1 |
FALSE |
| "TextBackgroundColorIndex" |
0x18 |
Leaf |
UINT8 |
|
1 |
FALSE |
| "PlainTextData" |
0x19 |
Leaf |
STRING |
|
Variable |
FALSE |
GIF Extensions After Image Metadata GIF Metadata Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| "AfterImageExtensions" |
0xFFF |
Tree |
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GIF Extensions After Image Level
| Name |
Id |
Type |
Value Type |
Value |
Value Length |
Read Only |
| One or more GIF extension levels |
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