hresults.tex

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% HTKBook - Steve Young and Julian Odell  24/11/97
%


\newpage
\mysect{HResults}{HResults}

\mysubsect{Function}{HResults-Function}

\index{hresults@\htool{HResults}|(}
\htool{HResults} is the \HTK\ performance analysis tool.
It reads in a set of label files (typically output
from a recognition tool such as \htool{HVite}) and compares them
with the corresponding reference transcription files.  
For the analysis of speech recognition output, the comparison
is based on a Dynamic Programming-based string alignment procedure.
For the analysis of word-spotting output, the comparison
uses the standard US NIST FOM metric.

When used to calculate the sentence accuracy using DP the basic 
output is recognition statistics for the whole file set in the format
\begin{verbatim}
   --------------------------- Overall Results -------------------
   SENT:  %Correct=13.00 [H=13, S=87, N=100]
   WORD:  %Corr=53.36, Acc=44.90 [H=460,D=49,S=353,I=73,N=862]
   ===============================================================
\end{verbatim}
The first line gives the sentence-level accuracy based on the 
total number of label files which are identical to the transcription
files.  The second line is the word accuracy based on the DP matches
between the label files and the transcriptions \footnote{
The choice of ``Sentence'' and ``Word'' here is the usual
case but is otherwise arbitrary.
\htool{HResults} just compares label sequences.  The sequences
could be paragraphs, sentences, phrases or words, and the labels
could be phrases, words, syllables or phones, etc.  Options exist
to change the output designations `SENT' and `WORD' to whatever
is appropriate.}.
In this second line,
$H$ is the number of correct labels, $D$ is the number of deletions,
$S$ is the number of substitutions, $I$ is the number of insertions and
$N$ is the total number of labels in the defining transcription files.
The percentage number of labels correctly recognised is given by
\begin{equation}
   \mbox{\%Correct} = \frac{H}{N} \times 100\%
\end{equation}
and the accuracy is computed by
\begin{equation}
   \mbox{Accuracy} = \frac{H-I}{N} \times 100\%
\end{equation}

In addition to the standard \HTK\ output format, 
\htool{HResults} provides an alternative similar to that used
in the US NIST scoring package, i.e.\
\begin{verbatim}
    |=============================================================|
    |           # Snt |  Corr    Sub    Del    Ins    Err  S. Err |
    |-------------------------------------------------------------|
    | Sum/Avg |   87  |  53.36  40.95   5.68   8.47  55.10  87.00 |
    `-------------------------------------------------------------'

\end{verbatim}


When \htool{HResults} is used to generate a confusion matrix, the
values are as follows:
\begin{description}
\item[\%c] The percentage correct in the row; that is, how many times a phone
     instance was correctly labelled.
\item[\%e] The percentage of incorrectly labeled phones in the row as
     a percentage of the total number of labels in the set.
\end{description}
An example from the HTKDemo routines:
\begin{verbatim}
====================== HTK Results Analysis =======================
  Date: Thu Jan 10 19:00:03 2002
  Ref : labels/bcplabs/mon
  Rec : test/te1.rec
      : test/te2.rec
      : test/te3.rec
------------------------ Overall Results --------------------------
SENT: %Correct=0.00 [H=0, S=3, N=3]
WORD: %Corr=63.91, Acc=59.40 [H=85, D=35, S=13, I=6, N=133]
------------------------ Confusion Matrix -------------------------
       S   C   V   N   L  Del [ %c / %e]
   S   6   1   0   1   0    0 [75.0/1.5]
   C   2  35   3   1   0   18 [85.4/4.5]
   V   0   1  28   0   1   12 [93.3/1.5]
   N   0   1   0   7   0    1 [87.5/0.8]
   L   0   1   1   0   9    4 [81.8/1.5]
Ins    2   2   0   2   0
===================================================================
\end{verbatim}
Reading across the rows, \%c indicates the number of correct instances
divided by the total number of instances in the row.  \%e is the
number of incorrect instances in the row divided by the total number
of instances (N).

Optional extra outputs available from \htool{HResults} are
\begin{itemize}
 \item   recognition statistics on a per file basis
 \item   recognition statistics on a per speaker basis
 \item   recognition statistics from best of N alternatives
 \item   time-aligned transcriptions
 \item   confusion matrices
\end{itemize}
For comparison purposes, it is also possible to assign two
labels to the same equivalence class (see {\tt -e option}).  
Also, the {\em null} label {\tt ???} is defined so that making any
label equivalent to the null label means that it will be
ignored in the matching process.  Note that the order of equivalence
labels is important, to ensure that label {\tt X} is ignored, the
command line option \verb+-e ??? X+ would be used.
Label files containing triphone labels of the form {\tt A-B+C} can be 
optionally stripped down to just the class name {\tt B} via the {\tt -s} 
switch.

The word spotting mode of scoring can be used to calculate hits,
false alarms and the associated figure of merit for each of a
set of keywords.
Optionally it can also calculate ROC information over a range of
false alarm rates.  A typical output is as follows
\begin{verbatim}
------------------------ Figures of Merit -------------------------
      KeyWord:    #Hits     #FAs  #Actual      FOM
            A:        8        1       14    30.54
            B:        4        2       14    15.27
      Overall:       12        3       28    22.91
-------------------------------------------------------------------
\end{verbatim}
which shows the number of hits and false alarms (FA) for two keywords
\texttt{A} and \texttt{B}.  A label in the test file with start time $t_s$
and end time $t_e$ constitutes a hit if there is a corresponding label
in the reference file such that $t_s < t_m < t_e$ where $t_m$ is the
mid-point of the reference label.

Note that for keyword scoring, the test
transcriptions must include a score with each labelled word spot
and all transcriptions must include boundary time information.

The FOM gives the \% of hits
averaged over the range 1 to 10 FA's per hour.  This is calculated
by first ordering all spots for a particular keyword according to
the match score.  Then for each FA rate $f$, the number of hits are counted
starting from the top of the ordered list and stopping when 
$f$ have been encountered.  This corresponds to \textit{a posteriori}
setting of the keyword detection threshold and effectively gives an
upper bound on keyword spotting performance.

\mysubsect{Use}{HResults-Use}

\htool{HResults} is invoked by typing the command line
\begin{verbatim}
   HResults [options] hmmList recFiles ...
\end{verbatim}
This causes \htool{HResults} to be applied to each {\tt recFile} in turn.  The
{\tt hmmList} should contain a list of all model names for which result
information is required.  Note, however, that since the context dependent parts
of a label can be stripped, this list is not necessarily the same as the one
used to perform the actual recognition.  For each {\tt recFile}, a
transcription file with the same name but the extension {\tt .lab} (or some
user specified extension - see the {\tt -X} option) is read in and matched with
it. The {\tt recfiles} may be master label files (MLFs), but note that even if  such an MLF is loaded using the {\tt -I} option, the list of files to be checked still needs to be passed, either as individual command line arguments or via a script with the {\tt -S} option. For this reason, it is simpler to pass the {\tt recFile} MLF as one of the command line filename arguments. For loading reference label file MLF's, the {\tt -I} option must be used. The reference labels and the recognition labels must have different file extensions.
The available options are
\begin{optlist}
  \ttitem{-a s} change the label \texttt{SENT} in the output to 
      \texttt{s}.

  \ttitem{-b s} change the label \texttt{WORD} in the output to 
      \texttt{s}.

  \ttitem{-c} when comparing labels convert to upper case.  Note that
      case is still significant for equivalences (see \texttt{-e} below).

  \ttitem{-d N} search the first \texttt{N} alternatives for each test label
      file to find the most accurate match with the reference labels.
      Output results will be based on the most accurate match to allow 
      NBest error rates to be found.

  \ttitem{-e s t}  the label {\tt t} is made equivalent to the
      label {\tt s}.  More precisely, {\tt t} is assigned to an equivalence
      class of which {\tt s} is the identifying member.

  \ttitem{-f} Normally, \htool{HResults} accumulates statistics for all
      input files and just outputs a summary on completion.
      This option forces match statistics to be output for each
      input test file.
      
  \ttitem{-g fmt} This sets the test label format to {\tt fmt}. 
      If this is not set, the {\tt recFiles} should be in the
      same format as the reference files.

  \ttitem{-h} Output the results in the same format as US NIST scoring 
      software.

  \ttitem{-k s} Collect and output results on a speaker by speaker basis
      (as well as globally).  \texttt{s} defines a pattern which is used 
      to extract the speaker identifier from the test label file name.
      In addition to the pattern matching metacharacters 
      \texttt{*} and \texttt{?}
      (which match zero or more characters and a single character 
      respectively), the character \texttt{\%} matches any character whilst
      including it as part of the speaker identifier.

  \ttitem{-m N} Terminate after collecting statistics from the first
      \texttt{N} files.  

  \ttitem{-n} Set US NIST scoring software compatibility.
      
  \ttitem{-p} This option causes a phoneme confusion matrix to
      be output.

  \ttitem{-s} This option causes all phoneme labels with the form
      {\tt A-B+C} to be converted to {\tt B}.  It is useful for
      analysing the results of phone recognisers using context dependent
      models.

  \ttitem{-t} This option causes a time-aligned transcription of
      each test file to be output provided that it differs from
      the reference transcription file.

  \ttitem{-u f} Changes the time unit for calculating false alarm
      rates (for word spotting scoring) to \texttt{f} hours (default is 1.0).

  \ttitem{-w} Perform word spotting analysis rather than string
      accuracy calculation.  

  \ttitem{-z s} This redefines the null class name to {\tt s}. 
  The default null class name is {\tt ???}, which may be difficult 
  to manage in shell script programming.

\stdoptG
\stdoptI
\stdoptL
\stdoptX

\end{optlist}
\stdopts{HResults}

\mysubsect{Tracing}{HResults-Tracing}

\htool{HResults} supports the following trace options where each
trace flag is given using an octal base
\begin{optlist}
   \ttitem{00001} basic progress reporting.
   \ttitem{00002} show error rate for each test alternative.
   \ttitem{00004} show speaker identifier matches.
   \ttitem{00010} warn about non-keywords found during word spotting.
   \ttitem{00020} show detailed word spotting scores.
   \ttitem{00040} show memory usage.
\end{optlist}
Trace flags are set using the \texttt{-T} option or the  \texttt{TRACE} 
configuration variable.
\index{hresults@\htool{HResults}|)}


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