June 23, 2020
A new way of generating and viewing relightable images has been applied to all Accurate Color images of Ambrosiana C73inf,
which includes the Latin (Arian) Commentary on Luke and Latin Moses (Latin Jubilees and the Testament of Moses).
The new Relight images can be found alongside the old WebRTI images in the
A less polished but more direct portal to the available relight html (and supporting) files is available here:
Earlier images were processed using Hemispherical Harmonics. The new images should offer higher fidelity. Feedback is always appreciated, especially about quality for purposes of scholarly analysis.
The same institution that brought us WebRTI has brought us “Relight,” including a fitter and a viewer:
Visual Computing Lab of CNR-ISTI,
Along with the new options for fitting relightable images, the good folks at Visual Computing Lab also offered some improvements over the WebRTI viewer. The most noticable improvement for casual users is the addition of the option of “visualize normals.” The default mouse/touch behavior is moving the light, rather than panning the image. Web developers have many more useful options for determining the initial view. I prefer to start with a dramatic raking angle. I can also set that angle to match one of the captured positions to facilitate fidelity comparisons.
One of the biggest improvements for the Jubilees Palimpsest Project from the perspective of data management is support for IIIF as a source of tiles. Tiles are important because a screen can never show all the available pixels at once. It saves time transfering data to load only the broad view at first and then greater detail only for the area to which the user zooms. In WebRTI the only option for storing tiles used static pregenerated tiles. For many users without an image server, this was fast and easy. However, the tens of thousands of tiny images for each RTI image was cumbersome for data management on the backend. With IIIF support, 9 JPEG2000 files (3 planes per file) contain all the data from which derivatives can be generated dynamically. However, as of June 20, 2020, the relight-viewer.js code available on GitHub seems to assume IIP Server in IIIF mode, not the actual IIIF Image API. The simple fix is to replace two lines (or segments of lines working from the minified files) and add two parameters to the HTML that calls the script.
The first substitution is to replace:
t.metaDataURL = t.server + "?IIIF=" + t.path + "/" + t.img + "/info.json";
t.metaDataURL = t.iiifServer + t.iiifPath + '/' + t.img + '.jp2/info.json';
The second substitution is to replace:
return t.iiifServer + t.iiifPath + '/' + image + '.jp2/'
If your IIIF server suppresses the .jp2 extension then remove it in both replacements.
Then you will want to define iiifServer and iiifPath when invoking the script.
For example, see the source code in:
Although the option to tune for fidelity is much appreciated,
RTI is fundamentally a simulation mediated by mathematical formulas.
The benefits of interactivity, extrapolation, interpolation, and enhancement are significant.
However, for scholarship, particularly judgments of whether a mark is a shadow, something on the surface, or a digital artifact,
it remains necessary to consult the raking images on which the RTI fitting is based.
The Jubilees Palimpsest makes all these images available in the archive: