pdfLaTeX supports using PNG files when using graphicx package. But today I encountered an error that one of my PNG graph “had an unknown graphics extension” compiling with pdfLaTeX.
After searching the internet I found the reason and the solution. Here I paste it as below.
graphicxpackage uses the first dot to find the extension. Package
grffilechanges the algorithm to check for known extensions (option
multidot, enabled by default):
That is, one of my PNG files has more than one dots in its file name. After including the package
grffile, the compiler ran pretty well. :-)