Tools - Settings - View - Thumbnails
The menu item "Tools → Settings → View → Thumbnails" configures the view type "thumbnails".
The distance (in pixels) between two images can be specified here.
The value in the input field "X" defines the horizontal spacing between two images.
The value in the input field "Y" defines the vertical spacing between two images.
If "Transparent" is not checked, the background color of images can be chosen after clicking the button.
The background color is shown above and below images in landscape orientation.
The background color is shown on the right and left of images in portrait orientation.
Background color - Transparent
If this setting is checked, the background of images is transparent.
If "No border" is not checked, the border color of images can be chosen after clicking the button.
If this setting is checked, the images are shown without borders.
If this setting is checked, the image is rotated based on its EXIF information saved by some cameras in the JPG file.
If this setting is checked, only files and no folders are shown in the view type thumbnails.
Make thumbnails for folders too
Show overlay icons
If this setting is checked, overlay icons are shown (if present) above the normal icons. Example of an overlay icon: Source code management (e.g. TortoiseSVN).
Make thumbnails for the text files
This setting specifies that thumbnails will show the start of text files whose file extension is entered in the input field.
If it is defined in the input field that thumbnails for text files are shown, the text font size can be specified here.