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If I open this jpeg (a single page from a comic) and set the zoom to “actual size”, it is not displaying at the correct size. The resolution of the image is 972x1400, but Sumatra PDF displays it smaller than that. This is on SumatraPDF-3.2. I tried both 32 and 64-bit portable versions, and the installed version 64-bit. They all do the same thing.

Additionally, I noticed that if I open a folder of images of varying sizes (a comic), “actual size” can end up being displayed very, very small.


“Actual size” is based on the data within the jpeg so it is
972 x 1400 at 144 dpi thus is correctly shown as 6.75 " x 9.72" (17.145 x 24.694 cm)
in my case that reports in SumatraPDF as Page Size: 17.15 x 24.69 cm

Normally the default dpi for jpg is considered half of 144 i.e.shown at 72 dpi thus in this case the image may look like it is half size but it is shown as per internal intent.

Likewise with PNG the “norm” is 96 dpi so sometimes they can also be scaled in a different fashion but SumatraPDF will consider the internal “scanned” value (when present) in preference to the common default.

You can use an image editor to alter the dpi to a default of 72 (or 96)

As an alternative you can change advance settings such as the
CustomScreenDPI = 200
or similar to make all images appear larger but the “actual size” will still be reported as above only the screen rendering will be twice as big, thus not recommended unless ALL your inputs need enlarging e.g. for a hi res screen.

As usual you could use two different shortcuts for different settings files
e.g. one to enlarge double resolution images and one to show other documents as per normal.resolution


Thank you for the reply. I assumed it might have had something to do with dpi. I did right-click the images to look at the dpi values, but I don’t know what dpi really means or how it’s used. I just started using Sumatra to try to read manga. The first one I read scaled as expected, but this one didn’t.

So after thinking about it, it appears setting CustomScreenDPI is exactly what I needed. The dpi for all images in a manga volume should be the same, so it only needs to be set at most once before reading each volume. Setting CustomScreenDPI to the same as the jpeg’s dpi gives the “actual size” that I would expect, but I can just pick an arbitrary value to get just the right amount of zoom. (I don’t actually need to view the images in “actual size” because that’s just an arbitrary size.) So with the press of a single button (using AutoHotKey to remap the shortcut) I can zoom in by a specific, desired amount. And another button can be used to zoom back out (fit to page). I just have to set CustomScreenDPI beforehand. I used to use IrfanView to read manga, and this is something that didn’t appear to be possible. (In IrfanView, there’s a “display multiplier %” for fullscreen mode, but changing it causes “fit to page” to no longer fit to page.)

So as far as I can tell, SumatraPDF is possibly the ideal program for reading manga. I’m switching from IrfanView after getting a larger monitor because IrfanView can’t display 2 pages at a time. With AutoHotKey, all the necessary shortcuts can be remapped to single keys on the numpad. (I have + for fullscreen, - for bookmarks, end for “actual size”, ins for “fit to page”.) I also have the left and right arrows on the numpad swapped, so I can advance to the next page using left instead of right, which feels much more natural when reading right to left. Sumatra doesn’t hide the mouse cursor in fullscreen like IrfanView, but for that I’m using a separate mouse hiding program, which can be started and closed thru AutoHotKey with a single button. (edit: This last one doesn’t work quite right at the moment because of windows antimalware, but anyway… I’ll have to do some searching to see if there’s a better alternative to Sumatra or not. The lack of mouse hiding seems to be the only thing missing that’s needed.)


There are two fullscreen modes F or F11 is more useful for browsing
but F5 will remove the pointer after a few seconds as it was intended for more limited classroom presentations.
I do not think SumatraPDF can allow changing dpi master setting “on the fly” like some of the other settings So that would require different start-ups, search the forum for example use of -appdata command which needs seperate start-up folders one for each set of preferences.
However you can pre-set the range of zoom values ( even removing those you don’t want/need) so that the zoom steps are exactly whatever you want e.g 144 196 200 etc.


Oh wow, I didn’t even notice the F5 presentation option. But it doesn’t seem to be able to do “book view” or “facing” at the same time. F5 just displays a single page. The delay before the mouse goes away is also much longer than I would want.

However you can pre-set the range of zoom values ( even removing those you don’t want/need) so that the zoom steps are exactly whatever you want e.g 144 196 200 etc.

This might be usable. I’ll have to tinker with it…


[Later edit]Agreed that F5 is single page only My test file was faulty
corrected by @SumatraPeter in the raised git hub issue F5 should work in both facing and book mode
although F11 does not hide cursor, so that could be raised as “issue” at if it is a residual problem for you


If anyone cares, the program I was trying to use before to hide the mouse cursor, AutoHideMouseCursor, actually works perfectly fine. The version I tried before caused windows antimalware executable to go nuts (very long delay before the program starts), but the x64 version doesn’t cause this for me. AutoHotKey starts and stops it with no problem.


Apologies for My Bad advice about F5 see @SumatraPeter s GOOD advice at