well, now the interval should work as expected

internal/slideshow/slideshow.go

@@ -18,22 +18,24 @@ import (
 func Start() {
 	loggo.Info("starting the image slideshow...", "interval: "+strconv.FormatFloat(config.Interval.Seconds(), 'f', 0, 64)+" seconds")
 	var sleepTime time.Duration
+	var scaleTime time.Duration
 	scaleImages := config.IsResolutionSet()
 	for {
 		var data []byte
 		image := watcher.GetRandomImage()
 		if scaleImages {
+			scaleTimestamp := time.Now()
 			tmp, error := scale(image)
 			if error != nil {
 				loggo.Error("encountered an error scaling an image", "image: "+image, error.Error())
 				continue
 			}
 			data = tmp
+			scaleTime = time.Since(scaleTimestamp)
 		}
 		if sleepTime > 0 {
 			time.Sleep(sleepTime)
 		}
-		sleepTime = time.Until(time.Now().Add(config.Interval))
 		if scaleImages {
 			error := setBackgroundPiped(data)
 			if error != nil {
@@ -47,6 +49,7 @@ func Start() {
 			}
 			loggo.Info("set new background image", "image: "+image)
 		}
+		sleepTime = config.Interval - scaleTime
 	}
 }