Black space between vertical pictures

I have been using yacreader on my iPhone and iPad for a while now, and I have to say that as an application both on the smartphone/tablet side and on the PC as a reader and server, I am getting along really well.
There is just one thing that I find annoying and I was wondering if there was a solution for that.
When reading Korean manhwa or Chinese manhua vertically, I noticed that between each image, this black line forms (as shown in the image below) :



From PC if I look at the images they have no black borders and if I merge them (for example with PhothoScape X) they look perfect.
At this point the only doubt is some “spacing” that YAC Reaeder on iOS (I have no way of knowing if it does the same thing on Android) puts between the images.

Is there any solution about this ?

Hmmm, this sounds like a rounding error, I think I've worked on this in the past but maybe I missed something. I'll try to fix it in the next release.