libgraphicsmagick++1-dev binary package in Ubuntu Focal amd64

 GraphicsMagick provides libraries in several programming languages to read,
 write and manipulate image files across a large number of formats, from the
 widely used jpeg, tiff, bmp or xpm to special-purpose formats such as fits or
 image formats found on some photo CDs. There are functions for finegrained
 image processing tasks, as well as conversion routines between the various
 image formats.
 .
 The GraphicsMagick library is a fork of ImageMagick and therefore offers
 an interface that is similar in features, but intended to be more stable
 across releases. While compatibility does not go so far that the
 GraphicsMagick library serves as a drop-in replacement for ImageMagick,
 conversion can usually be done with little effort.
 .
 This package contains the C++ development headers and library files needed to
 compile programs using the GraphicsMagick++ library.

Source package