■ Image thumbnail preview troubleshooter

When you browse folders full of photos and other images (JPG, PNG, GIF etc) it makes sense to switch to thumbnail mode. Right click "nowhere" to access the pane's background menu and you will find many options under Pane style submenu. You can choose normal or mini (smaller) thumbnails, and even combine thumbnails with file details. For bigger previews turn on the quick previewer panel (e.g. press <Ctrl+Q> keys). Through program options you can choose thumbnail pixel size; there are more thumbnail related tweaks in Advanced options (e.g. you can define the ratio between normal and mini thumbs and more).

picture thumbnails and larger preview pane

Remedies for thumbnail afflictions

Normally thumbnail image previews should "just work". xplorer² extracts previews using the windows thumbnail cache, so you can expect your previews to show up instantly, especially in folders you have browsed before. But should Maxwell's demon pay your computer a visit to increase the disarray, what can you do?

There are no one size fits all solutions for complex systems, but let us follow this not-so Bayesian network troubleshooter to root out some common image preview problems.

Check windows explorer. If a picture doesn't show in xplorer², see if the same picture shows up in windows explorer or not. Both programs use the same image cache, so this test will tell you if the problem is general or just in xplorer²
Thumbnail cache full? If you have lots of pictures, you may have used up all the space provided for thumbnails. In the past windows used local THUMBS.DB files in each folder, but nowadays there is a single database for all thumbnails. Try resetting it with disk cleanup tool and see how it goes.
Problem with just one format? If you can see previews for JPG but not for DNG, you are likely missing the plugin that creates the thumbnails for the problematic format. See if sagethumbs will cover your missing format.
Thumbnails ok but no preview? If xplorer²'s big preview pane doesn't work but thumbnails do, and you are using the Draft mode (tab), right click on the preview pane and double check that Text only menu item is not ticked.
At a stretch you may have limited the previewer to certain formats using m_msQVDraftExtList advanced registry tweak
Image preview in zipfolders. If your images are in zip, 7z and other archives, xplorer² will not show thumbnails if they are over a certain size. You can increase this limit from options (see General property page, "Byte file size limits for extracting... item in ZIP").
If you have problems with large pictures only, set the Thumbnail extraction limit from the same options property page to 0 (this should be default)

If you discover that your problem is usually with windows thumbnail cache, there is an advanced xplorer² option to stop using it altogether (see REGISTRY.TXT for GAOPT_VISTADDICONES or GAO2_NOVISTATHUMBS for version 4+). The drawback is that you lose fast thumbnails; sometimes you must choose the lesser of two evils.