[Plugin: Slideshow Gallery Pro] Wrong size giving black columns on the sides

I am using some pictures with exact size of 600×250 pixels. In the plugin configuration I also set:
– gallery width = 600 pixels
– gallery heigth = 250 pixels
The idea is to get no resizing of pictures necessary (and less calculations). Despite of this I get black columns on left and rigth side of the picture.

The reason is perhaps that the picture being shown is only 594×244 pixels. For some unknown reason it seems like there is an offset of -6 pixels for both width and heigth?

If I tick “Resize Images (width)” to yes, then I get rid of the black columns.

If I compensate for the offset by adding 6 in the settings:
– gallery width = 606 pixels
– gallery heigth = 256 pixels
I will also get rid of the black columns.

I have also set the slideshow border to “0px solid #FFFFFF”.

Shouldn’t the plugin settings output exact size of the picture?

https://www.ads-software.com/extend/plugins/slideshow-gallery-pro/