Most often, MEI is used for the preparation of a digital musical text based on an existing music document, or with the intention of rendering the encoded notation into a document or audio rendition. MEI can, however, be used to provide a different kind of digital reproduction of a source document, which relies on the description and provision of digital imagery. Both approaches may be combined, so that the encoding of the musical content and digital facsimiles may add different facets to the same MEI document.
12.1 Elements of the Facsimile Module
This module makes available the following elements for encoding facsimiles:
- facsimileContains a representation of some written source in the form of a set of images rather than as transcribed or encoded text.
- surfaceDefines a writing surface in terms of a rectangular coordinate space, optionally grouping one or more graphic representations of that space, and rectangular zones of interest within it.
- zoneDefines an area of interest within a surface or graphic file.
It is possible to have more than one facsimile element in this location. This is especially useful when multiple sources are encoded in the same file using the mechanisms described in chapter 11 Editorial Markup of these Guidelines. In this case, the decls (declarations) attribute of facsimile may be used to refer to a source defined in the document's header, as seen in the following example:
Within a facsimile element, each page of the source is represented by a surface element. Each surface may be assigned an identifying string utilizing the label attribute. In addition, it may encapsulate more detailed metadata about itself in a figDesc element. The coordinate space of the surface may be recorded in abstract terms in the ulx, uly, lrx, and lry attributes. For navigation purposes, surface has a startid attribute that accommodates pointing to the first object appearing on this particular writing surface.
Within surface elements, one may nest one or more graphic elements, each providing a reference to an image file that represents the writing surface. Multiple graphic elements are permitted in order to accommodate alternative versions (different resolutions or formats, for instance) of the surface image. In spite of changes in resolution or format, all images must contain the same content, i.e., the entire writing surface.
The preceding markup will provide the basis for most page-turning applications. Often, however, it is desirable to focus attention on particular areas of the graphical representation of the surface. The zone element fulfills this purpose:
The coordinates of each zone define a space relative to the coordinate space of its parent surface . Note that this is not necessarily the same coordinate space defined by the width and height attributes of the graphic that represents the surface. The zone coordinates in the preceding example do not represent regions within the graphic, but rather regions of the writing surface.
Because the coordinate space of a zone is defined relative to that of a surface, it is possible to provide multiple graphic elements and multiple zone elements within a single surface. In the following example, two different images representing the entire surface are provided alongside specification of two zones of interest within the surface:
A zone element may contain figDesc or graphic elements that provide detailed descriptive information about the zone and additional images, e.g., at a different/higher resolution, of the rectangle defined by the zone. The data objects contained within the zone may also be specified through the use of the data attribute, which contains ID references to one more elements in the content tree of the MEI file, such as a note, measure, etc.
Conversely, an element in the content may refer to the facsimile subtree using its facs attribute, which is made available by the att.facsimile attribute class. The last example could therefore be encoded with pointers in the other direction:
The pb element defined in the shared module makes special use of the facs attribute, in that it does not point to a zone, but a surface element instead. A pb marks the beginning of a page, so it can be concluded that all elements in the content tree which are encoded between any two pb elements encode musical symbols written on the page ( surface) referenced by the first of these two pb element's facs attribute.