This function gives the native pixel dimensions of an image:

(defun es-image-file-pixel-dimensions (file)
  (let* ((type (image-type file nil nil))
         (spec (list 'image :type type :file file)))
    (image-size spec t)))

When

(> (getf (cdr (doc-view-current-image)) :width)
   (car (es-image-file-pixel-dimensions
         (getf (cdr (doc-view-current-image)) :file))))

there is quality loss.

What I don't want to see is margins having a different width - for the same
reasons you wouldn't put a photograph in a frame in the top left corner.
Ideally I'd also center vertically (should the image be shorter than the
window) and add a window-configuration-change-hook (or there might be
an appropriate display-spec), so it's always centered. Unfortunately no
image-viewer that currently comes with emacs (image-mode ,doc-view-mode
,image-dired-display-image-mode) does this.

Evgeni


On Wed, Mar 6, 2013 at 1:01 PM, Tassilo Horn <tsdh@gnu.org> wrote:

> E Sabof <esabof@gmail.com> writes:
>
> > I've tried it, indeed it works much better. Might it be possible to
> > store the the "native" size, and raise the resolution automatically
> > when the zoom exceeds it?
>
> Well, the resolution should be increased and the doc reconverted when
> the up-scaled image becomes blurry.  But how should emacs know when you
> think it becomes blurry?
>
> > On a side note, might it be also possible to horizontally center the
> > image?  There is a pretty straight-forward way to do it, used in the
> > about-emacs screen.
>
> I guess this could be done somehow.  But do you want to center to make
> the contents a bit larger and not to see the margins?  If so, then
> slicing to the bounding box (`s b') followed by fitting to width (`W')
> may be the better approach.
>
> Bye,
> Tassilo
>