rockbox/manual/plugins/jpegviewer.tex

\subsection{JPEG viewer}
Open a .jpg file in the file browser to view it\opt{recorder,recorderv2fm,ondio,h1xx}
{ contents using Rockbox's greyscale library}. 
\note{When an audio file is playing the size of the image is limited as 
the decoding process needs to share memory with audio tracks. To be able viewing
bigger file you may need to stop playback.}

\fixme{use btnmap here -- make this table break more nicely}
\begin{table}
\begin{center}
    \begin{tabularx}{.8\textwidth}{lX}\toprule
    \btnhead
    \opt{recorder,recorderv2fm,h1xx,h300}{\ButtonUp\ / \ButtonDown\ / }
      \ButtonLeft\ / \ButtonRight
    & Move around in zoomed in image\\
    \opt{recorder,recorderv2fm}{\ButtonPlay}
    \opt{ondio}{\ButtonMenu}
    \opt{h1xx,h300}{\ButtonSelect}
    \opt{ipodcolor,ipodnano}{\ButtonScrollFwd}
    & Zoom in\\
    \opt{recorder,recorderv2fm}{\fixme{MENU}}
    \opt{ondio}{\ButtonMenu+\ButtonDown}
    \opt{h1xx,h300}{\ButtonMode}
    \opt{ipodcolor,ipodnano,ipod4g,ipodmini}{\ButtonScrollBack}
    & Zoom out\\
    \opt{recorder,recorderv2fm}{\ButtonFThree}
    \opt{ondio}{\ButtonMenu+\ButtonRight}
    \opt{h1xx}{\ButtonOn}
    \opt{h300}{\ButtonRec}
    \opt{ipodcolor,ipodnano}{\ButtonSelect+\ButtonRight}
    & Next jpeg in folder\\
    \opt{recorder,recorderv2fm}{\ButtonFTwo}
    \opt{ondio}{\ButtonMenu}
    \opt{h1xx}{\ButtonRec}
    \opt{h300}{\ButtonOn}
    \opt{ipodcolor,ipodnano}{\ButtonSelect+\ButtonLeft}
    & Previous jpeg in folder\\
    \opt{recorder,recorderv2fm,h1xx,h300}{\ButtonOff}
    \opt{ondio}{\ButtonOff}
    \opt{ipodcolor,ipodnano}{\ButtonSelect+\ButtonMenu}
    & Show menu\\\bottomrule
    \end{tabularx}
    \end{center}
\end{table}

The menu has the following entries.
\begin{description}
\item[Quit.] Quits the viewer and returns to the file browser.
\item[Toggle Slideshow Mode.] Enables or disables the slideshow mode.
\item[Change Slideshow Timeout.] You can set the timeout for the slideshow
  between 1 second and 20 seconds.
\item[Show Playback Menu.] From the playback menu you can control the 
playback of the currently loaded playlist and change the volume of you \dap.
\item[Return.] Returns you to the image
\end{description}

\note{JPEGs that use progressive scan encoding are not supported and will 
  produce an error.}