2006.08.04 14:05 "[Tiff] newbiequestion: [?] backup complete ifd > private ifd", by Karin Hoehne

thanx for your helpfull suggestions.

well, here's another newbie-cry-for-help. (hope, that's not too stupid.)

(this is refering to this: http://www.asmail.be/msg0055393448.html... just in case)

after reconsidering the natur of the described assignment and doing some further tiff-structure-research/libtiff-homework, i more or less came to following conclusions:

[1]

knowing about values of the tags won't help - what i really need is something like a numerical value-comparison.

note:

the goal is >not< anything like a real tag analyses, but something like a backup-system without the need of knowing anything about the tag-values (or possible private-tag-values). in other words: i just need something like a byte-copy/comparison.

------------------------------------------------------------------------- [2]

let's assume i have a tiff-file like this:

| header | ifd[0] | data |

... and in the very end, what i want to have is:

------------------------------------------------------------------------- [3]

i want to backup the ifd[0] >one< time and just leave it in what ever position in the file. since ifd[0] does not have any pointers to the backuped ifd[1], there shouldn't be any problems with the file, because ifd[1] is just a chunk of data. am i right with that assumption?

with every loading-function (in the to-be-programmed app) i want compare >every< (numerical) value of ifd[0] and the backup ifd[1]. if >anything< is different (e.g. a single bit), i want to copy the values of ifd[1] to ifd[0].

i have to admit: it was mentioned and i know, thet i >can< somehow copy the ifd, but i still couldn't figue aut >how<. (sorry... newbie)

------------------------------------------------------------------------- [4]

what i want to know about ifd[0] (and copy to ifd[1]) is something like this (copied elsewhere):

00000008 : 00 10 number of tags : 16

0000000A : 00 FF  00 03  00 00 00 01  00 01 00 00    whatever_tag[1]
00000016 : 01 00  00 04  00 00 00 01  00 00 02 40    whatever_tag[2]
00000022 : 01 01  00 04  00 00 00 01  00 00 01 80    whatever_tag[3]
0000002E : 01 02  00 03  00 00 00 01  00 01 00 00    whatever_tag[4]
0000003A : 01 03  00 03  00 00 00 01  00 01 00 00    whatever_tag[5]
...
000000BE : 01 28  00 03  00 00 00 01  00 02 00 00    whatever_tag[16]

000000CA : 00 00 00 00 pointer to next IFD (or 0)

it would be nice, if i could manage to get and compare >something< like a plain string of the bytes in the ifd:

001000FF00030000000100010000...... 00000000

(something like the tiffinfo -d option, only for the directory.)

------------------------------------------------------------------------- hope, anyone could help. i'm a little lost. :) thx again in advance /karin