Make head switching consistent across frames

JargeZ · Aug 19, 2023 · 8949c74 · 8949c74
1 parent cdcd25c
commit 8949c74
Showing 1 changed file with 5 additions and 5 deletions.
diff --git a/app/ntsc.py b/app/ntsc.py
@@ -223,7 +223,6 @@ def __init__(self, precise: bool, random: NumpyRandom):
 
         self._vhs_head_switching = False  # turn this on only on frames height 486 pixels or more
         self._head_switching_speed = 0  # 0..100 this is /1000 increment for _vhs_head_switching_point 0 is static
-        self._vhs_head_switching_point = 1.0 - (4.5 + 0.01) / 262.5  # 4 scanlines NTSC up from vsync
         self._vhs_head_switching_phase = (1.0 - 0.01) / 262.5  # 4 scanlines NTSC up from vsync
         self._vhs_head_switching_phase_noise = 1.0 / 500 / 262.5  # 1/500th of a scanline
 
@@ -332,7 +331,7 @@ def video_chroma_phase_noise(self, yiq: numpy.ndarray, field: int, video_chroma_
             U[y, :] = u
             V[y, :] = v
 
-    def vhs_head_switching(self, yiq: numpy.ndarray, field: int = 0):
+    def vhs_head_switching(self, yiq: numpy.ndarray, field: int, frameno: int):
         _, height, width = yiq.shape
         fY, fI, fQ = yiq
         twidth = width + width // 10
@@ -343,9 +342,10 @@ def vhs_head_switching(self, yiq: numpy.ndarray, field: int = 0):
             noise = x / 1000000000.0 - 1.0
             noise *= self._vhs_head_switching_phase_noise
 
+        vhs_head_switching_point = (self._head_switching_speed / 1000) * frameno
+
         t = twidth * (262.5 if self._output_ntsc else 312.5)
-        p = int(fmod(self._vhs_head_switching_point + noise, 1.0) * t)
-        self._vhs_head_switching_point += self._head_switching_speed/1000
+        p = int(fmod(vhs_head_switching_point + noise, 1.0) * t)
         y = int(p // twidth * 2) + field
         p = int(fmod(self._vhs_head_switching_phase + noise, 1.0) * t)
         x = p % twidth
@@ -588,7 +588,7 @@ def composite_layer(self, dst: numpy.ndarray, src: numpy.ndarray, field: int, fi
             self.video_noise(yiq, field, self._video_noise)
 
         if self._vhs_head_switching:
-            self.vhs_head_switching(yiq, field)
+            self.vhs_head_switching(yiq, field, frameno)
 
         if not self._nocolor_subcarrier:
             self.chroma_from_luma(yiq, field, fieldno, self._subcarrier_amplitude_back)