Image File Format

1
Image File Format

• Only focused in TIFF-Tag Image File Format
• Grayscale
• 8 bit
• Purpose-interchange of digital image data
• Goals
• Extensibility-capable to adapt new type of image
• Portable-different environment
• Revisable-edit, change process (not read only)

2

• Tag refers to files basic structure
• Tag provides information
• Width
• Length
• Number of pixel
• Store in Tag Directory
• Tag Directory have not set length/ number just a
  pointer-so can grow and adapt in future

3

• Image consist 2D array of number
• The array store color intensity of each pixel
  location
• TIFF format
• Header
• Image File Directories
• Data

4

• Arrangement of Header, IFD and Data in TIFF file

Header
Image File Directories
Data
5

• File Header
• First 8 byte of file
• Same format in all TIFF file and constant
• Contains first IFD offset
• Image File Directories-IFD
• Provides image information such as image width,
  length, bits per pixel, etc

6

• Data
• Contains real data for specific information such
  as pixel value and etc
• Can show after or before IFD

7
File Header Format

• Byte Order-How data will be read from file
• LSB-Intel(4949)
• MSB-Motorola(4D4D)
• Version-TIFF version number
• IFD Offset-First IFD offset or address
• MSB-must do swap 2 or 4 byte

8
IFD Format
Directory Entry
Image File Directories
9

• In IFD contains DE
• In first 2 byte IFD, provides number of DE, m
• DE has 12 byte each
• So in each IFD, total number of DE is
• m x 12

10

• DE format
• Tag
• Type of information the entries contains
• First 2 bytes
• Data Type
• 2 bytes
• Data type of information and data size

11

• TIFF data type
• 1 byte 8 bit unsigned integer
• 2 ASCII 8 bit bytes that store ASCII codes
  (last byte must be null)
• 3 short 16 bit (2 byte) unsigned integer
• 4 long 32 bit (4 byte) unsigned integer
• 5 rational 2 longfirst is numerator. Second
  denominator

12

• Length
• Length of the information
• 4 bytes
• Depend to Tag
• variable real size
• S Length x Size that define from Type

13

• Value
• 4 bytes
• Data contents
• If S gt 4 bytes value contains is not real
  information just an offset or address or pointer
  for real information
• Else value contains real information