Reading large dimension PNGs Error: Qt cannot read PNG file

[Ak]

I hope you are all well.

I am having an issue reading some larger dimension  PNG files (30720 x 30720).

I can read the same files in console, but in Qt I get the message:

 

     'Qt cannot read PNG file'

Is this a resources limitation related to the added overhead of running jqt? 

Is there a way to increase the allottable resource amount?

Or is there some other setting I need to adjust that allows me to access the larger PNGs in jqt?

Thank you

Ak

 

[Daniikk1012]

It appears Qt itself by default limits memory available to the image loader.

In order to load it, you would somehow need to increase that limit, or use another png loading method (If you're using png addon, maybe it has a way to choose a different loader?).

In C++ you would call QImageReader::setAllocationLimit(): https://forum.qt.io/topic/143069/loading-large-images/8

In J you might try to call this method using "cd", as it's a static method, but since it's C++ it's probably mangled, and that mangling is dependent on what compiler was used to compile Qt.

Or create a wrapper DLL in C++ that defines an extern "C" function that calls this method, which will avoid mangling, and then call that from J.

Not a J expert though, maybe there is an easier way I'm missing.

вторник, 21 октября 2025 г. в 06:28:31 UTC+5, Ak:

[trx2358...@yahoo.com]

Do you have a link to a public PNG file which displays this error?

Sent from Yahoo Mail for iPhone

[Devon McCormick]

You could create one - if your machine has enough memory - with a statement like this:

   (30720 30720 3?@$256) write_image 'Large.png'

On Tue, Oct 21, 2025 at 6:21 AM trx2358-discord via forum <fo...@jsoftware.com> wrote:

Do you have a link to a public PNG file which displays this error?

Sent from Yahoo Mail for iPhone

To unsubscribe from this group and stop receiving emails from it, send an email to forum+un...@jsoftware.com.

--

Devon McCormick

Flâneur

[Ak]

You can generate a file with the same protocol I use with these instructions.

My apology I don't know your name. Thx for looking at it. 

Ak

NB. This is the protocol I used to cause the error.
NB.  The line causes the error in jqt.
NB.                0 read_sample data_path
NB. This executes in a J-Console Session.
NB.
NB. dimensions-> 30720 30720
NB. image_data -> Image
NB. data_path -> path to storage folder.
NB. set_sample -> Pixel format ARGB format 
NB. write_path/read_path -> storage folder
NB. read_sample -> Read out image_data from selected file from data_path
NB.
NB.                       Write template
NB. This generates a png file of ~700 MB in the path you designate.
NB. Writes a png to the folder called data_folder on the path.
NB.           [string_filename]  write_sample  [image_data]
NB.         
NB.           'big_png_00' write_sample image_data
NB.
NB.                       Read template
NB.           [folder_item_number] read_sample  [data_path]
NB.
NB.           0 read_sample  data_path
NB.          


load 'png'
image_data =: 254{.,(|.128 *"0 2 (#:i.16)),(255 *"0 2 ((16?16){"2 (#:i.16))),(255 *"0 2 (#:i.16)),(128 *"0 2 ((16?16){"2 (#:i.16)))
'u31 u32' =: <.2^31 32
unpak =: u32&|
pak =: unpak&.(+&u31)
set_sample =: [: pak ([: , 256 256 256 256 (#.) _4 ]\ ])"1
data_path =: hostpathsep 'c:/data_folder/'
read_sample =: [: , [: readpng_jpng_  ([: ; [ {  [: {."1 [: dirtree ]) :: (0%00)

     write_sample =: 4 : 0
n=. ('.png',~])&.>(write_path,])&.><x
p=. , set_sample y
n writepng_jpng_ ~(30720 30720 $ p)
)


NB.                   Write
     'big_png_00'   write_sample  image_data

NB.                   Read           This line results in -> QT cannot read PNG file.
   $  0 read_sample data_path
       0 read_sample data_path

[bill lam]

Try disable Qt image routines by

USEQTPNG_z_=: 0

load 'png'

.....

[Ak]

Thank you Bill.

This works.

Ak