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\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).