Option to auto-adjust the level of 0 IRE based on the back porch

vhsdecode/field.py

@@ -383,9 +383,19 @@ def hz_to_output(self, input):
             if self.rf.options.export_raw_tbc:
                 return input.astype(np.single)
             else:
+                ire0 = self.rf.DecoderParams["ire0"]
+                if self.rf.options.ire0_adjust and input.size == self.outlinecount * self.outlinelen:
+                    blank_levels = np.empty(self.outlinecount)
+                    for i in range(0, self.outlinecount):
+                        blank_levels[i] = np.median(
+                            input[i * self.outlinelen + self.ire0_backporch[0] : i * self.outlinelen + self.ire0_backporch[1]]
+                        )
+                    blank_levels = np.sort(blank_levels)
+                    ire0 = np.mean(blank_levels[int(self.outlinecount / 3) : int(self.outlinecount * 2 / 3)])
+                    ldd.logger.debug("calculated ire0: %.02f", ire0)
                 return hz_to_output_array(
                     input,
-                    self.rf.DecoderParams["ire0"]
+                    ire0
                     + self.rf.DecoderParams["track_ire0_offset"][
                         self.rf.track_phase ^ (self.field_number % 2)
                     ],
@@ -1079,6 +1089,7 @@ def fix_badlines(self, linelocs_in, linelocs_backup_in=None):
 class FieldPALShared(FieldShared, ldd.FieldPAL):
     def __init__(self, *args, **kwargs):
         super(FieldPALShared, self).__init__(*args, **kwargs)
+        self.ire0_backporch = (96, 160)
 
     def refine_linelocs_pilot(self, linelocs=None):
         """Override this as most regular band tape formats does not use have a pilot burst.
@@ -1101,6 +1112,7 @@ class FieldNTSCShared(FieldShared, ldd.FieldNTSC):
     def __init__(self, *args, **kwargs):
         super(FieldNTSCShared, self).__init__(*args, **kwargs)
         self.fieldPhaseID = 0
+        self.ire0_backporch = (74, 124)
 
     def refine_linelocs_burst(self, linelocs=None):
         """Override this as it's LD specific

vhsdecode/main.py

@@ -108,6 +108,13 @@ def main(args=None, use_gui=False):
         default=0.1,
         help="Multiply top/bottom IRE in json by 1 +/- this value (used to avoid clipping on RGB conversion in chroma decoder).",
     )
+    luma_group.add_argument(
+        "--ire0_adjust",
+        dest="ire0_adjust",
+        action="store_true",
+        default=False,
+        help="Automatic adjust of ire0 based blanking level",
+    )
     luma_group.add_argument(
         "--high_boost",
         metavar="High frequency boost multiplier",
@@ -391,6 +398,7 @@ def main(args=None, use_gui=False):
     rf_options["skip_hsync_refine"] = args.skip_hsync_refine
     rf_options["export_raw_tbc"] = args.export_raw_tbc
     rf_options["tape_speed"] = args.tape_speed
+    rf_options["ire0_adjust"] = args.ire0_adjust
 
     extra_options = get_extra_options(args, not use_gui)
     extra_options["params_file"] = args.params_file

vhsdecode/process.py

@@ -569,6 +569,7 @@ def __init__(
         )
 
         export_raw_tbc = rf_options.get("export_raw_tbc", False)
+        ire0_adjust = rf_options.get("ire0_adjust", False)
         is_color_under = vhs_formats.is_color_under(tape_format)
         write_chroma = (
             is_color_under
@@ -602,6 +603,7 @@ def __init__(
                 "export_raw_tbc",
                 "fm_audio_notch",
                 "chroma_offset",
+                "ire0_adjust",
             ],
         )(
             self.iretohz(100) * 2,
@@ -631,6 +633,7 @@ def __init__(
             export_raw_tbc,
             rf_options.get("fm_audio_notch", 0),
             int(self.DecoderParams.get("chroma_offset", 5) * (self.freq / 40.0)),
+            ire0_adjust,
         )
 
         # As agc can alter these sysParams values, store a copy to then