[help-texinfo] Errors related to images when using makeinfo

[Nicolas]

Hello,

I try to convert a texinfo file to the DocBook format. We need to create
a DocBook file in order to use a contextual help browser such as yelp.

I use the following command:
makeinfo --docbook cinelerra.texi

And errors such as this one appear:
cinelerra.texi:1314: avertissement: commande @image avec un fichier «
images/magnify.txt » illisible: Aucun fichier ou répertoire de ce type.

It's written in French. Here's the English translation:
cinelerra.texi:1314: warning: command @image with file «
images/magnify.txt » cannot be read: no such file or directory of that
type

Here's the line #1314 in cinelerra.texi:
background rendering directory.  The @image{images/magnify,5mm,5mm,.png}
browse button for

At first, my goal was to only generate pdf and html manuals. So I used
texi2html and texi2pdf. The way those utilities work surprised me. I had
to generate pdf files out of the png images to generate the pdf file,
since texi2pdf expect images to be in the pdf format.

Now, it seems makeinfo expect .txt images to be found! 

I read on the following page:
http://www.gnu.org/software/texinfo/manual/texinfo/html_node/Image-Syntax.html

"If you do not supply the optional extension (fifth) argument, makeinfo
first tries filename.png; if that does not exist, it tries filename.jpg.
If that does not exist either, it complains. (We cannot support GIF
format directly due to software patents.)"

I tried without any fifth extension, and that did not changed anything.
Why doesn't makeinfo find the .png images?

What could I do to solve that problem?

Thank you.
Nicolas.