Update rbga_to_black_bg.py

rbga_to_black_bg.py

@@ -2,7 +2,7 @@ import torch
 
 class RGBA_Black_Background:
     """
-    Composites an RGBA image over a white background and outputs RGB.
+    Composites an RGBA image over a black background and outputs RGB.
     Assumes input image in ComfyUI tensor format: float32, 0..1, shape [B,H,W,C].
     """
 
@@ -37,10 +37,10 @@ class RGBA_Black_Background:
             raise ValueError(f"Expected 3 (RGB) or 4 (RGBA) channels, got {c}")
 
         rgb = image[..., :3]
-        a   = image[..., 3:4]  # keep as [B,H,W,1]
+        a   = image[..., 3:4]  # [B,H,W,1]
 
-        # Composite: out = rgb * a + white * (1-a) ; white=1
-        out = rgb * a + (0.0 - a)
+        # Black background composite: bg=0 => out = rgb*a + 0*(1-a) = rgb*a
+        out = rgb * a
 
         return (out.clamp(0.0, 1.0),)
 
@@ -51,4 +51,4 @@ NODE_CLASS_MAPPINGS = {
 
 NODE_DISPLAY_NAME_MAPPINGS = {
     "RGBA_Black_Background": "RGBA to Black Background RGB (Black Background)"
-}
+}