On Mon, 18 Jun 2012 "Birnbaum, David J" djbpitt@pitt.edu wrote:
Dear Digital Medievalist,
For a couple of new Internet editions of medieval manuscripts I've procured high-resolution tiff images, which I'm publishing with a "magnifying glass" overlay. This is in a "responsive" context, so the components of the page, including the images, resize to fit the window dimensions. There's a sample at:
Have you considered embedding images in the DjVu format?
I guess it would not be possible to automatically resize the image, but there would be some other advantages.
The current images were prepared quickly for a demo, and are not of consistent size or resolution. I would now like to go back to get this part of the site up to production quality, and I would be grateful for advice about how to manage the images, an area where I don't have much (= any) knowledge of best practice. I'd like small image files that load quickly,
Even big DjVu images should load quickly, that's what the format has been designed for.
and I think I don't mind slightly lossy compression if that would reduce the file size substantially--but if that's a mistake, I'd be grateful for a warning. I think there are two questions:
DjVu allows both lossy and lossless compression.
- What's an appropriate file format and resolution (size, dpi,
color depth, etc.) for the base image, the one that is displayed in full to the right of the transcription, and that resizes as the user resizes the window? Currently the image files are in jpg format and vary in size from about 2M down to 250k. I can regenerate them all at a common size, resolution, color depth, etc. from the original tiffs, but I don't know whether there is any sense of best practice concerning what that size should be. If I go the lossy route, what's a reasonable value?
- What's an appropriate degree of magnification for the
magnifying-glass inset view? Currently the magnifying glass inset always shows the image at 200% of the actual file size (not the size of the page as displayed without magnification in the browser window!). You can see the difference by comparing, say, folio 30v (about 2MB) to 284r (about 270k), where the magnification is much greater in the former than the latter. I can set the level of magnification anywhere I'd like, but is there any agreement about best practice here?
Using DjVu allows the user to select the size and magnification of the magnifying glass.
By way of orientation in the question: the purpose of the full image is to allow the user to see the image conveniently alongside the transcription,
Djvu allows to store the transciption as "hidden text". You can view it with the original scan as background, but the fragment pointed with mouse may be made visible also in the status line.
verifying any moments where our editorial judgment might appear surprising or questionable. The point of the magnified inset is to let the user examine details that may not be visible at lesser magnification, such as erasures, corrections, etc. My casual impression is that 30v looks pretty good and loads reasonably quickly (although quicker would be better), but I don't place great confidence in my own casual impressions.
The DjVu viewer allows user to choose the magnification of the image.
Of course using DjVu has only some drawbacks, like the need to install the DjVu viewer and browser plugin.
Best regards
Janusz