Yep, a file offset is the position from the beginning of the file (in bytes) - remember the first byte of a file is at offset 0.
Example: File has the following data: abcdefghijklmnopqrstuvwxyz offset 3: d offset 5: f offset 9: j When working with tiff's, don't forget to check the byte order field in the header at offsets 0-1. It will be either 4D4D hex (MM ascii) for Motorola ordering, also known as Big Endian; or 4949 hex (II ascii) for Intel ordering, also known as Little Endian. This is important when reading the offsets from the file: MM has the most significant byte first, II has the least significant byte first. This is only important if this value indicates a different format than the chip you are using (Motorola or Intel). If it is different, all short and long ints will need to have their byte ordering reversed. Examples: Offset:Byte 00:02 01:04 02:0A 03:01 04:03 2 byte number (16 bit short int) at offset 0: MM: 0204 hex = 516 dec II: 0402 hex = 1026 dec 2 byte number (16 bit short int) at offset 1: MM: 040A hex = 1034 dec II: 0A04 hex = 2564 dec 4 byte number (32 bit long int) at offset 0: MM: 02040A01 hex = 33819137 dec II: 010A0402 hex = 17433602 dec 4 byte number (32 bit long int) at offset 1: MM: 040A0103 hex = 67764483 dec II: 03010A04 hex = 50399748 dec If you're head's not spinning yet, let me know if you need a semi-efficient algorithm to do this byte order reversal. James -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John Hebert Sent: Thursday, July 22, 2004 9:29 AM To: [email protected] Subject: [brlug-general] What exactly is a "file off-set"? Howdy, I am trying to understand the TIFF file format and I came across a term: "file off-set". I kinda have an idea what this is, but I am not sure. I think it referring to a position in the file where actual image data starts, so that a header section can exist to provide meta-data about the image. (?) Can anyone define what a file off-set is or point me to a good explanation? Thanks, John __________________________________ Do you Yahoo!? Vote for the stars of Yahoo!'s next ad campaign! http://advision.webevents.yahoo.com/yahoo/votelifeengine/ _______________________________________________ General mailing list [email protected] http://brlug.net/mailman/listinfo/general_brlug.net
