Ivo, I am not aware of such a function (if it exists I am sure someone will advise both you and me), however, I have found that as long as the original images are suitably resized before use (ie not much larger than the size required in the showbox), then the delay is minimal unless there are a massive amount of images.

I always resize all images to a maximum of 1200px wide before use in any website.

Hello Ivo

As Esahc writes, then the images should be resized to fit the area of the slideshow/showbox.

You could use the free IrfanView to resample and then save optimized for web.

This way an image that is maybe 960.000 kb could be reduced to 34 kb - and with no significant loss in quality.

There is also other gallery viewers. If you have really many images, you could use the wow-slider. This slider has a feature where you can specify on-demand.

This means that images will not be loaded until short time before they are needed.

The wow-slider is not free but there is a testversion where the images will be "watermarked".

But else - do as Esahc tells - resize the images. And if the image only need to be 600px wide, then it will only be 1/4 the size, of the image that is 1200 wide.

If you resize the images and then compress ( as hard as possible ) then there will be a significant change in the loading time.

It is ALWAYS a good idea to make  images not bigger than needed, before using them in X5.

Kind regards

John S.