How to open a remote image in external program

Question

Say you have a big big image that you can't really look at with emacs' image support, org-mode or image-mode buffer. You want to use program like gwenview or feh where you can zoom in and out easily and drag it around.

Answer 1

(defun view-remote-image (remote-path)
  (interactive "f")
  (let ((temp-file (make-temp-file "remote-image-"))
        (image-viewer-program "feh"))
    (copy-file remote-path temp-file t)
    (start-process "view-remote-image" nil image-viewer-program temp-file)))

Works with other type of file with bit modification. Big Big images (like generated UML diagram) would be a major use cases. open-with doesn't work out of box, as you'll be passing command like feh /ssh:user@host:/path/to/img.png which will fail.

Answer 2

I personally use the open-with package (link) as follows, mostly from dired, for local images:

(use-package openwith
  :init
  (openwith-mode 1)
  
  :config
  (setq openwith-associations
        (list
         (list (openwith-make-extension-regexp
                '("png" "gif" "jpeg"))
               "feh"
               '(file))
         (list (openwith-make-extension-regexp
                '("pdf"))
               "gwenview"
               '(file)))))

where the extensions are just meant as an example. I don't use the programs you listed, and therefore the code above is not tested. It should nevertheless work with any program.

For the case of remote images, I use instead sshfs in the CLI, and treat all images as being local.