If you provide separately created thumbnails, use the following option, which is the default:
[Graphics]
; ExtrGraphThumbnail = Named (default,
; use original name plus ExtrGraphSuffix)
ExtrGraphThumbnail=Named
When ExtrGraphThumbnail=Named, you provide a thumbnail version of the first image in each extract. You must create the thumbnails yourself, using a third-party graphics tool, and store them in the same directory with the output graphics. Each thumbnail must have the same file name as the corresponding output graphic, but with a suffix added to the base name. You specify the suffix as follows:
[Graphics]
; ExtrGraphSuffix = suffix for file name of first graphic in an
; extract, used in the predefined <$$_extrgraph> macro
to identify
; its thumbnail
ExtrGraphSuffix=tn
Name thumbnail after output graphic
Except for the suffix, each thumbnail must have the same name as the corresponding output graphic.
Place thumbnail in project directory
Each thumbnail you create must be placed in the same directory with the corresponding output graphic; this might be different from the directory where your original graphics are located.
For example, suppose your document references the following graphic:
You must provide the following thumbnail for jaguar.jpg:
D:\MyDoc\graphics\jaguartn.jpg
If DITA2Go does not find a properly named thumbnail for the first graphic in an extract, you get either a broken link or just the alt text in the replacement code.
If there is no graphic in the extract, the value of <$$_extrgraph> for that extract is NULL, and the literal name extrgraph appears in the replacement code wherever you specified <$$_extrgraph>.