Convert PNG to 300pdi

[Stone-D]

Hi,

I want
to export a graph's image to a 300pdi-png (printing). Here's what I do:

 

First I export the graph to a png with the standard LV-VI. I re-open the file, locate the IHDR-Header, shift the index by 17 (which is the end of the IHDR) and place the pHYs-Header (from a 300pdi-PNG created by Photoshop)in between the IHDR and the IDAT,  as required. (See Snipet; hope you don't mind the german captions ^^)

 

So far
so good, but the file gets corrupt after my modifications....guess I've done some mistakes here.

Greets,

Stoney

Message Edited by Stone-D on 03-24-2010 06:20 AM

[Andrey_Dmitriev]

At the first, try to set "prepend array or string size? (T)" of the Write to Binary File primitive to false (its true by default), because this added 4 additional bytes at the beginning of the file and png header gets corrupted.

Andrey.

[muks]

Should it not be dpi instead of pdi

[Andrey_Dmitriev]

---

muks wrote:
Should it not be dpi instead of pdi

---

Hmmm... "Per Dot Inch" also not so bad. But "ipd" - this will be definitoively totally wrong!

[muks]

Just wanted to confirm that it means the same irrespective what the name is.

[Stone-D]

---

Andrey Dmitriev wrote:

---

muks wrote:
Should it not be dpi instead of pdi

---

Hmmm... "Per Dot Inch" also not so bad. But "ipd" - this will be definitoively totally wrong!

---

ups, my bad....

---

Andrey Dmitriev wrote:

At the first, try to set "prepend array or string size? (T)" of the Write to Binary File primitive to false (its true by default), because this added 4 additional bytes at the beginning of the file and png header gets corrupted.



Andrey. 

---

Thanks, but the file is still corrupt... 

[Andrey_Dmitriev]

---

Stone-D wrote:

Thanks, but the file is still corrupt... 

---

Not sure if other parts of the header should be changed or not (may be some offsets values should be corrected).

You have three possibilities in general:

1. Check byte to byte that your new file still compliant with  RFC2083.

2. Use ImageMagick (something like "convert -units PixelsPerInch -density 300 inFile.png outFile.png")

3. Use  libpng (as dll - this can be hard if you haven't experience with using external code in LabVIEW)

Andrey.

[Stone-D · Accepted solution]

omg, just found my error.............The string constant which contains the dpi-header wasn't set to hex...