png header calibration format and index location

[John Pierson]

Hi
this leads on from another thread but the question has changed alot so:

Does anyone know the format that vissual assistant stored the pixel cordinates within a .png map file

the information stored must be both the location and real word corrdiantes of each of the highlighted pixel locations that you sellet [in my case 4]

also they might be stored in a certian possition, but all i seem to get by reading the header information is the word: Version, as the header, and the word: National, in the text information, this is on a good range of header ranges of 'indexes' i have tried from -10 to 20, and all of them seem to have the same value on them.

attatched are the VI made to read or write the .png information, and an example image with the header information i neeed in there.

chears for any help at all!!

John P.

[GerdW]

Hi John,

it's been a long time since I dealt with PNG files directly...

But your PNG contains header entries like "NIIMAQ" and "TXtVersion". The rest of the header (before IDAT [ImageDATa] at offset 0x02f5) looks like being either encrypted or packed. So you better ask NI directly!


Message Edited by GerdW on 02-15-2008 02:16 PM

[John Pierson]

Hi GerdW
where did you find those entries? they might be what i'm looking for, where they in a specific index or can the VI i suplied not find them?
chears for reply!
John P.

[GerdW]

Hi John,

I don't have LV at hand so I just looked at the PNG (with a hex editor).
"NIIMAQ" is found at 0x003f, "TXtVersion" at 0x02b4. The official PNG image data header "IDAT" is found at 0x02f5. (All offsets from file start.)

But the rest doesn't make (a lot of) sense so you better ask a local NI tech advisor!

[rsw]

Hi John,

Thanks for posting a new thread regarding this question, it helps to group different questions. I'm afraid the actual information your after is propritary and therefore I can't give you any more details, If you do want to get all the info for how the header files are organized then I'm afraid you'll need to do some digging with a Hex editor for the parts you require.

Some information on chunks inside PNG files:

http://en.wikipedia.org/wiki/Portable_Network_Graphics#File_header

All the best,

Message Edited by rsw on 02-18-2008 04:26 AM