The PIL show() method looks for the default viewer. How do I change this to a different viewer (of my choice)?

[Peter Otten]

Paul St George wrote:

> Thank you.
> You are very right. The show() method is intended for debugging purposes
> and is useful for that, but what method should I be using and is PIL the
> best imaging library for my purposes? I do not want to manipulate
> images, I only want to show images (full screen) on an external display.
> I want to use Python to control the timing of the images.
> 
> And, out of curiosity, as I will probably use a different method - how
> do I find out what commands can be used as parameters for show()? I read
> the docs at
> <https://pillow.readthedocs.io/en/5.1.x/reference/Image.html
> #PIL.Image.Image.show>,
> but I am none the wiser.

If you look into the source code

https://github.com/python-pillow/Pillow/blob/master/src/PIL/Image.py#L1967

after a few indirections

show --> _show --> _showxv --> ImageShow.show

you will end up in the file

https://github.com/python-pillow/Pillow/blob/master/src/PIL/ImageShow.py

which is short enough to read completely ;)

At first glance it looks like the command argument is silently discarded, so 
here's plan B:

It turns out that you can register() Viewer instances, and the pre-
registered viewers for unixoids -- and thus probably the Pi are 
DisplayViewer and XVViewer.

Using these as a template I came up with the following simple viewer that 
shows an image with firefox:

#!/usr/bin/env python3
import os
import sys

from PIL import Image, ImageShow


class Firefox(ImageShow.UnixViewer):

    # store the image in a format understood by the browser
    format = "jpeg"

    def get_command_ex(self, file, **options):
        return ("firefox",) * 2

    def show_file(self, file, **options):
        quote = ImageShow.quote

        command, executable = self.get_command_ex(file, **options)

        # firefox returns immediately, so let's sleep a few seconds
        # to give it time to actually open the image file
        command = "(%s %s; sleep 10; rm -f %s)&" % (
            command, quote("file://" + file), quote(file)
        )
        os.system(command)
        return 1


# the -1 means our viewer will be inserted before the others
# and thus become the default
ImageShow.register(Firefox(), -1)


if __name__ == "__main__":
    try:
        file = sys.argv[1]
    except IndexError:
        print("Please provide an image file", file=sys.stderr)
    else:
        image = Image.open(file)
        image.show()


Here's another, even simpler one:

class Gwenview(ImageShow.UnixViewer):
    def get_command_ex(self, file, **options):
        return ("gwenview",) * 2