Portrait photo scrolling maxes out CPU

[AussieSteve]

Does anyone know why I can flick the mouse scroll wheel and have XnView MP whizz through images in a directory really fast if the JPEG images are shot in landscape made, yet when it hits a group of JPEG images shot in portrait mode it grinds to a slow crawl and the CPU usage shoots up to 100% as it struggles to scroll through them? According to the LED temperature display on my ASUS Z690 motherboard, when rapidly scrolling through landscape images, the CPU temperature hovers around 54-57°C yet when doing the same with portrait orientated images,it shoots up to 84-89°C. The zoom factor on preview doesn't seem to make much difference. My storage devices are all NVMe PCIe v4.0 SSD's, i9 12900K CPU, 64GB DDR5 RAM. If I shoot the image in portrait but have the camera export them as landscape so the photos is sideway, images shot portrait behave the same as landscape, but they appear sideways which is inconvenient and annoying. Any thoughts are appreciated. Thanks.

[MasonGilbert]

Bump.

[masterjp]

Which resolution do your pictures have (longest side)? Bigger than 3000 pixels?
Do you have exif informations in your jpeg files?
Do you use a file filter to exlude unnessary files (e.g. non picture files)?

I did not see any problems on my computer with slower hardware than yours.
But it is possible, that portrait photos need more time to view them in browser window.
Digital cameras (e.g. canon) always save their photos in landscape mode!
If you have a photo which is taken in portrait mode,
the camera only save a exif orientation tag with an angle to define the portrait view.

If XnViewMP load the portrait jpeg file, it will rotate your portrait picture from landscape view to portrait mode.
This could take time, if your picture has a big size. But middle or high class computers
should do this in a very short time and without big CPU usage!
XnViewMP use in most cases a few cpu cores.
More cpu cores are used in batch conversion mode, if you set a higher cpu core usage.

[AussieSteve]

JPEG images are 6000x4000 pixels landscape, 4000x6000 portrait.
Yes there is EXIF data in each image, the same quantity of EXIF for both portrait and landscape.
My Canon EOS R6 Mark II has the option to rotate photos shot in portrait when exported from the camera to PC so that in Windows File Explorer they are orientated the same as they were shot. If I open the portrait shots in any program they display in portrait layout.
When I flick the mousewheel on landscape pics it whizzes through then so fast it's hard to keep up they are changing so rapidly until it hits a portrait shot then out goes the boat anchor and CPU maxes out as it crawls through successive portrait shots. The difference in scrolling speed would be around 20 times faster for landscape shots. As a comparison, if I shot at 20 frames/sec, in landscape flicking the mouse wheel in preview mode looks like a video as the images zip past so fast, whereas with portrait shots it becomes a slideshow 1 next pic every 2 seconds. It make sno difference how much I zoom in or out in preview, the speed difference is still staggering.

[xnview]

could you send us some sample files?

[Giklab]

This actually happens in Faststone too, so it may not be specific to XnView.