I've recently switched from Tiger to Gromit as I wanted separate html pages for my images. Anyway, I tend to have large numbers of photos in a folder, and so thumbnail downloading on the index pages can take a bit of time to complete. Would it be possible to implement "lazy loading" of thumbnails on index pages?
Technically possible, I suppose, but I have no plans to implement it. It's a personal thing - I hate lazy loading, because it always makes a page feel sluggish to me. And one of the better API's for doing it doesn't work in Safari, which has too large a share of the visitor traffic to ignore. You end up having to build in a backstop method to handle the noncompliant browser.
It also sometimes kills SEO, by the way, because the search bots don't see all of the page content.
I've got some pages with over 400 thumbnails on them (about 3MB of images), and a web host that's almost 2000 miles away, but those pages load before I have time to scroll down. It clocks in at about 1MB of content per second. I have the gut feeling that lazy loading is a solution to a problem that is gradually going away (like using srcset to feed different sized images to different sized devices, to save bandwidth).
One additional tidbit for those watching from the Peanut Gallery...
This doesn't apply to Gromit, but in my newer skins, in which I'm using JustifiedGallery to present the thumbnails, using a lazy loader is completely impossible. The script that lays out the thumbnail table needs to have all of them to construct the layout.
The issue with long download times for my larger index pages has been eliminated. What was the fix? For some reason, I had JAlbum's "Save thumbnails with high JPEG compression quality" ticked. I've now unticked it, and index page downloads are now so much faster.
Yes, that will produce somewhat better-looking thumbnails, but at the price of larger file sizes. The real killer is choosing HiDPI thumbnails, which is a big help for visitors with Retina displays, but the files end up being twice the dimensions, and often more than twice the file size.
Alas, there's no free lunch. Sharper images require bigger files.