About:

Library to extract various information from the header of JPEG (Joint Photographic Experts Group) image files.

Download:

Version 1.1

Properties:

FileName

Access:
Get

Description:
Returns the name of the image file the class stores the information for.
(This will be the last filename you called the ReadFile() method with.)

FileSize

Access:
Get

Description:
Returns the size of the image file the class stores the information for

Width

Access:
Get

Description:
Returns the width of the main image

Height

Access:
Get

Description:
Returns the height of the main image

BitDepth

Access:
Get

Description:
Returns the bit-depth of the main image

Precision

Access:
Get

Description:
DCT precision of the main image.
Usually either 8-bit or 12-bit

Encoding

Access:
Get

Description:
Encoding method of the main image, or "Unknown encoding method" if unknown

Terminated

Access:
Get

Description:
Specifies whether the JPEG file was properly terminated.
This is very useful since un-terminated images will often cause unsuspecting image loading routines to choke, unfortunately VB's LoadPicture() is amongst these..

Extension

Access:
Get

Description:
Extension structure and version used in this file i.e. JFIF or Exif

XDensity

Access:
Get

Description:
Horizontal resolution of the main image

YDensity

Access:
Get

Description:
Vertical resolution of the main image

Density

Access:
Get

Description:
JFIF image density (Resolution units)
Possible values are; "Pixels", "Pixels / inch" or "Pixels / cm"

Methods:

ReadFile()

Description:
This is the core of the class, it parses and validates the file it's passed, then exposes the information it finds through the various properties of the class.

Parameters:

Name	Description
inFile	The full path of the file to parse

Return:
True if the file was correctly parsed and validated as an JPEG image file, False if not

DensityString()

Description:
Converts a JFIF density to a readable string description

Parameters:

Name	Description
inMode	Input density mode

Return:
String containing the density name, or "Unknown" if not known.

ClearInfo()

Description:
Internal method to clear all the data currently stored in the class.

FlipWord()

Description:
Converts a big-endian Word to a little endian Word.

Parameters:

Name	Description
inWord	Word value in big-endian format to convert

Return:
Little endian conversion.

SWordToDWord()

Description:
Converts a signed Word to an unsigned Word

Parameters:

Name	Description
inWord	Signed Word value to convert

Return:
Unsigned word value stored in a DWord to prevent overflow problems.

User defined types:

typChunkID

Description:
Generic JPEG chunk header

Members:

Name	Description
cSig	Chunk signature (Should be 0xFF)
cType	Chunk type ID
cSize	Chunk size

typSOFInfo

Description:
JPEG Start Of Frame tag information structure

Members:

Name	Description
sofPrecision	Sample precision
sofHeight	Frame height
sofWidth	Frame width
sofComponents	Number of channels

typAPP0Info

Description:
JPEG APPlication 0 (JFIF) information structure

Members:

Name	Description
appIdentity	Signature string for APP0 segment, should be "JFIF" but could theoretically be set to other values since the APPn segments are application defined.
appNULL	Null terminator for signature string
appMajor	Major JFIF version
appMinor	Minor JFIF version
appDensity	Resolution units (See the Density property)
appXDens	Horizontal resolution measured in density units
appYDens	Vertical resolution measured in density units
appTNWidth	Thumbnail width, or 0 if not present
appTNHeight	Thumbnail height of 0 if not present

typFrameInfo

Description:
Internal structure used to store information for each frame

Members:

Name	Description
Width	Frame width
Height	Frame height
BitDepth	Frame bit-depth
Precision	Frame channel size (See the Precision property)
Encoding	Frame encoding method string

API:

CopyMemory