Update app.py

app.py

@@ -2,45 +2,49 @@ import gradio as gr
 from PIL import Image
 import numpy as np
 
-def brightness_to_white_alpha(img, bg_img=None, invert_opacity=False):
-    if img is None:
+def combine_opacity_layers(top_img, bg_img, invert_opacity=False):
+    if top_img is None or bg_img is None:
         return None
 
-    # Step 1: Convert input to RGB and compute brightness
-    img_rgb = img.convert("RGB")
-    img_np = np.array(img_rgb).astype(np.float32)
-    brightness = np.dot(img_np[..., :3], [0.299, 0.587, 0.114])
+    # Convert both to RGB and resize
+    top = top_img.convert("RGB")
+    bg = bg_img.convert("RGBA").resize(top.size)
+    top_np = np.array(top).astype(np.float32)
 
+    # Compute brightness from top image
+    brightness = np.dot(top_np[..., :3], [0.299, 0.587, 0.114])
     if invert_opacity:
         brightness = 255 - brightness
+    alpha_top = (brightness / 255.0).clip(0, 1)  # shape (H, W)
 
-    alpha = brightness.clip(0, 255).astype(np.uint8)
+    # Get alpha from background image
+    bg_np = np.array(bg).astype(np.float32) / 255.0
+    alpha_bg = bg_np[..., 3]  # shape (H, W)
 
-    # Step 2: Create solid white RGBA image
-    height, width = alpha.shape
-    white_rgb = np.full((height, width, 3), 255, dtype=np.uint8)
-    white_rgba = np.dstack((white_rgb, alpha))  # shape (H, W, 4)
-    white_img = Image.fromarray(white_rgba, mode="RGBA")
+    # Multiply alpha channels
+    combined_alpha = (alpha_top * alpha_bg).clip(0, 1)
 
-    # Step 3: Overlay white image on background (if provided)
-    if bg_img:
-        bg = bg_img.convert("RGBA").resize(white_img.size)
-        composite = Image.alpha_composite(bg, white_img)
-        return composite
-
-    return white_img
+    # Create output RGBA: white RGB + combined alpha
+    height, width = combined_alpha.shape
+    white_rgb = np.ones((height, width, 3), dtype=np.float32)  # all white
+    out_rgba = np.dstack((white_rgb, combined_alpha)) * 255
+    out_img = Image.fromarray(out_rgba.astype(np.uint8), mode="RGBA")
+    return out_img
 
 # Gradio UI
 iface = gr.Interface(
-    fn=brightness_to_white_alpha,
+    fn=combine_opacity_layers,
     inputs=[
-        gr.Image(type="pil", label="Input Image"),
-        gr.Image(type="pil", label="Optional Background Image"),
-        gr.Checkbox(label="Invert Brightness → Alpha", value=False)
+        gr.Image(type="pil", label="Top Brightness-Based Image"),
+        gr.Image(type="pil", label="Base Opacity Image (with alpha)"),
+        gr.Checkbox(label="Invert Top Brightness", value=False)
     ],
-    outputs=gr.Image(type="pil", label="Final Output"),
-    title="💡 White Brightness Layer + Optional Background",
-    description="Generates a pure white image with brightness as transparency. Optionally overlays it on a background."
+    outputs=gr.Image(type="pil", label="Combined Opacity Image"),
+    title="🔁 Combine Two Opacity Images (Multiply Alphas)",
+    description=(
+        "Takes two images and multiplies their opacity (alpha). Output is solid white "
+        "with combined alpha values. Useful for stacking brightness masks."
+    )
 )
 
 if __name__ == "__main__":