Re: [Gimp-user] Can't open extremely large .PNG

["Liam R. E. Quin" <liam holoweb net>]

On Wed, 2016-10-12 at 10:08 +0200, Deixis wrote:
> Does anyone know any tricks on how to resize extremely large images?
> I can't
> even open this computer generated .PNG.

I'm going to guess you are using a Linux system in this answer. Life is
too short for me to try telepathy.


If you run the file command on the image file in a terminal,
file foo.png
or
identify foo.png
do you get a size in pixels?

I routinely open 10,000 x 20,000 pixel images in gimp.

A good rule of thumb is the amount of memory you need will be
width * height * 4 (assuming an 8-bit colour image)
in bytes, e.g. for a 100,000 x 37,000 pixel image it's
100000 * 37000 * 4
which gives 14800000000 bytes
dividing by 1024 * 1024 (megabytes) gets
14114 megabytes
and dividing that by 1024 gives
13.7 gigabytes.

So to open this (fictional) image you'd want probably 16G of RAM or
more in your 64-bit computer. On a 32-bit computer you'd want at least
20GBytes of swap.

The size of the image file on disk just reflects how well or badly the
PNG compression has worked, but if it's worked well, the image could
easily need over 100G of memory, which you could do by adding a large
amount of swap space and being very patient.

Without more information about the image and your setup it's hard to
guess and give more advice on which tools would be best.

Liam