> I think that's sufficiently fast. (Keep in mind that a 4k screen is about 8.5mp.) How fast do you want your slideshow to be?
A modern iPhone can capture at up to 48MP. If the performance scales linearly with pixel count, that would put tapping on a thumbnail to the full size being ready at over half a second. That's going to feel laggy. Now you can throw storage at the problem and pre-compute a downscaled intermediate, sure, but that doesn't fix it when you send the photo to someone else or whatever.
And competitive phones are doing 200mp captures (which is stupid in its own right but phone manufacturers and doing stupid things, name a more iconic duo)
At least JPEG contains downscaled thumbnails embedded into it as part of the EXIF stream. There's no need for the receiving device to rescale it again.
Pretty sure these newer formats do the same.
That thumbnail is for grid-size, it's generally 50kb or less in size which ends up being around 300x240 or up to 500x500 on newer codecs.
It'll be visibly low-res and blurry until the full size decodes for full screen. Hence why I said "when tapping on a thumbnail"
Oh, I missed the “tapping on” part.