I resized the images, and then changed the proportions in the gallerydata.xml file to match.

I am facing the same challenge. My original images are something like width/height 4k/7k or vice versa 7k/4k pixels.

I am generating gallery.xml with a script that scales the width and height to max 800 pix for longer side.

When still referring to original image size of 4k/7k I don't get the whole image into auto viewer.

Do I by default need to have also images scaled to max 800px in order auto viewer work ?

Below snippets of my screens/scripts/gallery.xml.
<?xml version="1.0" encoding="UTF-8" ?><gallery frameColor="0xFFFFFF" frameWidth="0" imagePadding="160" displayTime="3" enableRightClickOpen="false">
<image>
  <url>images/1.jpg</url>
  <caption></caption>
  <width>800</width>
  <height>534</height>
</image>

<image>
  <url>images/2.jpg</url>
  <caption></caption>
  <width>800</width>
  <height>534</height>
</image>

<image>
  <url>images/3.jpg</url>
  <caption></caption>
  <width>800</width>
  <height>534</height>
</image>

<image>
  <url>images/4.jpg</url>
  <caption></caption>
  <width>534</width>
  <height>800</height>
</image>

---- below the original size of the images shown in the parenthesis [width][height] and stdout how I create gallery.xml with the script.

Creating XML file for Autoviewer.
---------------------------------
Sorting images by date.
Sorting images in reverse order.

[6436][4295] - - Created Image Entry for:1.jpg whose width is 800 and whose height is 534.
[7360][4912] - - Created Image Entry for:2.jpg whose width is 800 and whose height is 534.
[7360][4912] - - Created Image Entry for:3.jpg whose width is 800 and whose height is 534.
[4912][7360] - - Created Image Entry for:4.jpg whose width is 534 and whose height is 800.