[tex-live] texlive under ubuntu cannot find proper .bb file for png image file

[Jin Huang]

Dear all,

I just switched from WinXP+MikTeX to ubuntu+TexLive. I have a latex 
document which can be correctly compiled into dvi previously.  However, 
it doesn't work now.

I have minimized the document to highlight problem as follows:

================= begin of a.tex ===============
\documentclass{article}
\usepackage{graphicx}
\DeclareGraphicsExtensions{.png}
\begin{document}
\begin{figure}
  \includegraphics{img.png}
\end{figure}

\end{document}
================= end of a.tex ===============

The img.png is a image file put in the same directory with a.tex, and 
img.bb is generated from ImageMagick with the following content:

%%BoundingBox: 0 0 210 592

It seems that when latex reads \includegraphics{img.png}, it doesn't go 
to find the corresponding bb file, or cannot find it.

I have also tried to remove the suffix of img.png in the tex document. 
It doesn't work still.

The document can be compiled use pdflatex correctly. Adding the option 
[pdftex] to the package graphicx also works.  But I want to dvi format 
output.

Any ideas?

Best regards,

Jin