Add --exposures option to tesstrain.sh

This flag can be used to specify multiple different exposure levels
for a training. There was some code already in tesstrain_utils.sh
to deal with multiple exposure levels, so it looks like this
functionality was always intended.

The default usage does not change, with exposure level 0 being the
only one used if --exposures is not used.

training/tesstrain.sh

@@ -24,6 +24,7 @@
 #    --output_dir OUTPUTDIR     # Location of output traineddata file.
 #    --overwrite                # Safe to overwrite files in output_dir.
 #    --run_shape_clustering     # Run shape clustering (use for Indic langs).
+#    --exposures EXPOSURES      # A list of exposure levels to use (e.g. "-1 0 1").
 #
 # OPTIONAL flags for input data. If unspecified we will look for them in
 # the langdata_dir directory.

training/tesstrain_utils.sh

@@ -26,6 +26,7 @@ OVERWRITE=0
 RUN_SHAPE_CLUSTERING=0
 EXTRACT_FONT_PROPERTIES=1
 WORKSPACE_DIR="/tmp/tesstrain"
+EXPOSURES=0
 
 # Logging helper functions.
 tlog() {
@@ -98,6 +99,16 @@ parse_flags() {
                 FONTS=( ${ARGV[$j]} )
                 IFS=$ofs
                 i=$j ;;
+            --exposures)
+                exp=""
+                while test $j -lt ${#ARGV[@]}; do
+                    test -z ${ARGV[$j]} && break
+                    test `echo ${ARGV[$j]} | cut -c -2` = "--" && break
+                    exp="$exp ${ARGV[$j]}"
+                    j=$((j+1))
+                done
+                parse_value "EXPOSURES" "$exp"
+                i=$((j-1)) ;;
             --fonts_dir)
                 parse_value "FONTS_DIR" ${ARGV[$j]}
                 i=$j ;;
@@ -226,8 +237,8 @@ phase_I_generate_image() {
         err_exit "Could not find training text file ${TRAINING_TEXT}"
     fi
     CHAR_SPACING="0.0"
-    EXPOSURE="0"
 
+    for EXPOSURE in $EXPOSURES; do
         if (( ${EXTRACT_FONT_PROPERTIES} )) && [[ -r ${BIGRAM_FREQS_FILE} ]]; then
             # Parse .bigram_freqs file and compose a .train_ngrams file with text
             # for tesseract to recognize during training. Take only the ngrams whose
@@ -256,6 +267,7 @@ phase_I_generate_image() {
             local outbase=${TRAINING_DIR}/${LANG_CODE}.${fontname}.exp${EXPOSURE}
             check_file_readable ${outbase}.box ${outbase}.tif
         done
+    done
 }
 
 # Phase UP : Generate (U)nicharset and (P)roperties file.
@@ -359,10 +371,9 @@ phase_E_extract_features() {
         par_factor=1
     fi
     tlog "\n=== Phase E: Extracting features ==="
-    TRAIN_EXPOSURES='0'
 
     local img_files=""
-    for exposure in ${TRAIN_EXPOSURES}; do
+    for exposure in ${EXPOSURES}; do
         img_files=${img_files}' '$(ls ${TRAINING_DIR}/*.exp${exposure}.tif)
     done