I'm working on a Omeka project (it's going pretty well so far) but we're not happy with the image quality of the thumbnails. The pictures look good when they are full sized but not when they are thumbnails. Is there any way I can improve this?
I'm not that familiar with this level of technical problems, so if I can provide more information that would be helpful please let me know.
What exactly about them doesn't look good? Are they too small, too big, or bad for some other reason?
It's mostly that they aren't very sharp. The pictures have lots of small details in them that don't show up that well in the thumbnails.
Is there anything to do about that?
What kind of images are you working with?
Omeka creates JPEG thumbnails, which are usually fine quality-wise for the size thumbnails are displayed at. Some kinds of images, like screenshots, have lots of small detail and hard edges that don't work as well with JPEG, though.
The easy things to tweak are the thumbnail size constraints, which are editable in the Site Settings page. Obviously, bigger thumbnails will look better, but there will always be some loss in sharpness and detail when resizing images.
They are JPEG (I assume - the uploads are anyway).
The pictures are of board games, decks of cards, toys, things like that which have small pieces. Is there an alternative for the thumbnails that is better for that?
But I will check out the size and see if that helps. Thanks!
Okay, not that surprisingly changing the size didn't really help. Any other ideas?
Can you share an example of one of your originals and a bad thumbnail that's generated from it? (Or, an Omeka item show page showing the problem?)
Seeing the results you're currently getting should help make it clear if there's anything you can do to improve things.
Sure. If I post a link can you access it? (I'll try that anyway)
In the photo, the details are clear, but in the thumbnail not so much.
There are some quality parameters for ImageMagick that could make some difference in how much detail is preserved in a thumbnail. You'd have to hack those kinds of changes into the Omeka core code if you wanted to make them.
Still, the major issue I think you're having here is one of size. You're trying to keep very small details visible, and the size of the image is going to be by far the biggest factor in what users can clearly see.
So, the small thumbnail version of the image you linked to is admittedly unclear, but a thumbnail's really just supposed to be a quick preview.
On the other hand, the "fullsize" derivative of the same image is much better, because it's much bigger (note, the "fullsize" derivative isn't the same as the full, archival image, it's just Omeka's name for the bigger derivative).
Your best bets for better-looking images are to change your theme to use the "fullsize" derivative more often, or to increase the size constraints for the thumbnails. (Remember, updating the size constraints only affects newly-uploaded images, or you can use the Image Resize plugin to resize previously-uploaded images.)