\chapter{Implementation notes}\label{implement}
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The CImage library is derived from the wxImage code collated and
developed by Alejandro Aguilar-Sierra.

The original code had wxImage derived from the same base class
as used by other implementation classes such as ImaGIF. To read a file,
a temporary ImaGIF (or other) object was created, and then the data was
copied into the wxImage object, and the temporary object deleted.

I have rearranged things a bit so that CImage is derived from CObject,
and contains a pointer to an implementation object derived CImageImpl.
File I/O and other functionality is routed from CImage to the CImageImpl-derived
object. When the CImage is saved as a different format, the implementation
object is changed (requiring copying of some members).

I have also eliminated dependencies on wxWindows, made use of CString
instead of character pointers, corrected some memory leaks, replaced the
DIB-writing code since the wxImage implementation appeared not to work,
converted the demo app to MFC, and written the on-line help (which could
do with expansion).

