Adding support for changing background color

Summary: Adds support to hard_rgb_blend and hard blending shaders in shader.py (HardPhongShader, HardGouraudShader, and HardFlatShader) for changing the background color on which objects are rendered

Reviewed By: nikhilaravi

Differential Revision: D21746062

fbshipit-source-id: 08001200f4339d6a69c52405c6b8f4cac9f3f56e

pytorch3d/renderer/blending.py

@@ -19,7 +19,7 @@ class BlendParams(NamedTuple):
     background_color: Sequence = (1.0, 1.0, 1.0)
 
 
-def hard_rgb_blend(colors, fragments) -> torch.Tensor:
+def hard_rgb_blend(colors, fragments, blend_params) -> torch.Tensor:
     """
     Naive blending of top K faces to return an RGBA image
       - **RGB** - choose color of the closest point i.e. K=0
@@ -32,14 +32,31 @@ def hard_rgb_blend(colors, fragments) -> torch.Tensor:
               of the faces (in the packed representation) which
               overlap each pixel in the image. This is used to
               determine the output shape.
+        blend_params: BlendParams instance that contains a background_color
+        field specifying the color for the background
     Returns:
         RGBA pixel_colors: (N, H, W, 4)
     """
     N, H, W, K = fragments.pix_to_face.shape
     device = fragments.pix_to_face.device
-    pixel_colors = torch.ones((N, H, W, 4), dtype=colors.dtype, device=device)
-    pixel_colors[..., :3] = colors[..., 0, :]
-    return pixel_colors
+
+    # Mask for the background.
+    is_background = fragments.pix_to_face[..., 0] < 0  # (N, H, W)
+
+    background_color = colors.new_tensor(blend_params.background_color)  # (3)
+
+    # Find out how much background_color needs to be expanded to be used for masked_scatter.
+    num_background_pixels = is_background.sum()
+
+    # Set background color.
+    pixel_colors = colors[..., 0, :].masked_scatter(
+        is_background[..., None],
+        background_color[None, :].expand(num_background_pixels, -1),
+    )  # (N, H, W, 3)
+
+    # Concat with the alpha channel.
+    alpha = torch.ones((N, H, W, 1), dtype=colors.dtype, device=device)
+    return torch.cat([pixel_colors, alpha], dim=-1)  # (N, H, W, 4)
 
 
 def sigmoid_alpha_blend(colors, fragments, blend_params) -> torch.Tensor:

pytorch3d/renderer/mesh/shader.py

@@ -39,13 +39,16 @@ class HardPhongShader(nn.Module):
         shader = HardPhongShader(device=torch.device("cuda:0"))
     """
 
-    def __init__(self, device="cpu", cameras=None, lights=None, materials=None):
+    def __init__(
+        self, device="cpu", cameras=None, lights=None, materials=None, blend_params=None
+    ):
         super().__init__()
         self.lights = lights if lights is not None else PointLights(device=device)
         self.materials = (
             materials if materials is not None else Materials(device=device)
         )
         self.cameras = cameras
+        self.blend_params = blend_params if blend_params is not None else BlendParams()
 
     def forward(self, fragments, meshes, **kwargs) -> torch.Tensor:
         cameras = kwargs.get("cameras", self.cameras)
@@ -57,6 +60,7 @@ class HardPhongShader(nn.Module):
         texels = interpolate_vertex_colors(fragments, meshes)
         lights = kwargs.get("lights", self.lights)
         materials = kwargs.get("materials", self.materials)
+        blend_params = kwargs.get("blend_params", self.blend_params)
         colors = phong_shading(
             meshes=meshes,
             fragments=fragments,
@@ -65,7 +69,7 @@ class HardPhongShader(nn.Module):
             cameras=cameras,
             materials=materials,
         )
-        images = hard_rgb_blend(colors, fragments)
+        images = hard_rgb_blend(colors, fragments, blend_params)
         return images
 
 
@@ -130,13 +134,16 @@ class HardGouraudShader(nn.Module):
         shader = HardGouraudShader(device=torch.device("cuda:0"))
     """
 
-    def __init__(self, device="cpu", cameras=None, lights=None, materials=None):
+    def __init__(
+        self, device="cpu", cameras=None, lights=None, materials=None, blend_params=None
+    ):
         super().__init__()
         self.lights = lights if lights is not None else PointLights(device=device)
         self.materials = (
             materials if materials is not None else Materials(device=device)
         )
         self.cameras = cameras
+        self.blend_params = blend_params if blend_params is not None else BlendParams()
 
     def forward(self, fragments, meshes, **kwargs) -> torch.Tensor:
         cameras = kwargs.get("cameras", self.cameras)
@@ -146,6 +153,7 @@ class HardGouraudShader(nn.Module):
             raise ValueError(msg)
         lights = kwargs.get("lights", self.lights)
         materials = kwargs.get("materials", self.materials)
+        blend_params = kwargs.get("blend_params", self.blend_params)
         pixel_colors = gouraud_shading(
             meshes=meshes,
             fragments=fragments,
@@ -153,7 +161,7 @@ class HardGouraudShader(nn.Module):
             cameras=cameras,
             materials=materials,
         )
-        images = hard_rgb_blend(pixel_colors, fragments)
+        images = hard_rgb_blend(pixel_colors, fragments, blend_params)
         return images
 
 
@@ -266,13 +274,16 @@ class HardFlatShader(nn.Module):
         shader = HardFlatShader(device=torch.device("cuda:0"))
     """
 
-    def __init__(self, device="cpu", cameras=None, lights=None, materials=None):
+    def __init__(
+        self, device="cpu", cameras=None, lights=None, materials=None, blend_params=None
+    ):
         super().__init__()
         self.lights = lights if lights is not None else PointLights(device=device)
         self.materials = (
             materials if materials is not None else Materials(device=device)
         )
         self.cameras = cameras
+        self.blend_params = blend_params if blend_params is not None else BlendParams()
 
     def forward(self, fragments, meshes, **kwargs) -> torch.Tensor:
         cameras = kwargs.get("cameras", self.cameras)
@@ -283,6 +294,7 @@ class HardFlatShader(nn.Module):
         texels = interpolate_vertex_colors(fragments, meshes)
         lights = kwargs.get("lights", self.lights)
         materials = kwargs.get("materials", self.materials)
+        blend_params = kwargs.get("blend_params", self.blend_params)
         colors = flat_shading(
             meshes=meshes,
             fragments=fragments,
@@ -291,7 +303,7 @@ class HardFlatShader(nn.Module):
             cameras=cameras,
             materials=materials,
         )
-        images = hard_rgb_blend(colors, fragments)
+        images = hard_rgb_blend(colors, fragments, blend_params)
         return images
 
 

tests/test_blending.py

@@ -4,6 +4,7 @@ import unittest
 
 import numpy as np
 import torch
+from common_testing import TestCaseMixin
 from pytorch3d.renderer.blending import (
     BlendParams,
     hard_rgb_blend,
@@ -128,7 +129,7 @@ def softmax_blend_naive(colors, fragments, blend_params):
     return pixel_colors
 
 
-class TestBlending(unittest.TestCase):
+class TestBlending(TestCaseMixin, unittest.TestCase):
     def setUp(self) -> None:
         torch.manual_seed(42)
 
@@ -156,7 +157,7 @@ class TestBlending(unittest.TestCase):
 
     def test_hard_rgb_blend(self):
         N, H, W, K = 5, 10, 10, 20
-        pix_to_face = torch.ones((N, H, W, K))
+        pix_to_face = torch.randint(low=-1, high=100, size=(N, H, W, K))
         bary_coords = torch.ones((N, H, W, K, 3))
         fragments = Fragments(
             pix_to_face=pix_to_face,
@@ -164,14 +165,21 @@ class TestBlending(unittest.TestCase):
             zbuf=pix_to_face,  # dummy
             dists=pix_to_face,  # dummy
         )
-        colors = bary_coords.clone()
-        top_k = torch.randn((K, 3))
-        colors[..., :, :] = top_k
-        images = hard_rgb_blend(colors, fragments)
-        expected_vals = torch.ones((N, H, W, 4))
-        pix_cols = torch.ones_like(expected_vals[..., :3]) * top_k[0, :]
-        expected_vals[..., :3] = pix_cols
-        self.assertTrue(torch.allclose(images, expected_vals))
+        colors = torch.randn((N, H, W, K, 3))
+        blend_params = BlendParams(1e-4, 1e-4, (0.5, 0.5, 1))
+        images = hard_rgb_blend(colors, fragments, blend_params)
+
+        # Examine if the foreground colors are correct.
+        is_foreground = pix_to_face[..., 0] >= 0
+        self.assertClose(images[is_foreground][:, :3], colors[is_foreground][..., 0, :])
+
+        # Examine if the background colors are correct.
+        for i in range(3):  # i.e. RGB
+            channel_color = blend_params.background_color[i]
+            self.assertTrue(images[~is_foreground][..., i].eq(channel_color).all())
+
+        # Examine the alpha channel is correct
+        self.assertTrue(images[..., 3].eq(1).all())
 
     def test_sigmoid_alpha_blend_manual_gradients(self):
         # Create dummy outputs of rasterization

tests/test_render_meshes.py

@@ -77,6 +77,7 @@ class TestRenderMeshes(TestCaseMixin, unittest.TestCase):
             image_size=512, blur_radius=0.0, faces_per_pixel=1
         )
         rasterizer = MeshRasterizer(cameras=cameras, raster_settings=raster_settings)
+        blend_params = BlendParams(1e-4, 1e-4, (0, 0, 0))
 
         # Test several shaders
         shaders = {
@@ -85,7 +86,12 @@ class TestRenderMeshes(TestCaseMixin, unittest.TestCase):
             "flat": HardFlatShader,
         }
         for (name, shader_init) in shaders.items():
-            shader = shader_init(lights=lights, cameras=cameras, materials=materials)
+            shader = shader_init(
+                lights=lights,
+                cameras=cameras,
+                materials=materials,
+                blend_params=blend_params,
+            )
             renderer = MeshRenderer(rasterizer=rasterizer, shader=shader)
             images = renderer(sphere_mesh)
             filename = "simple_sphere_light_%s%s.png" % (name, postfix)
@@ -105,7 +111,10 @@ class TestRenderMeshes(TestCaseMixin, unittest.TestCase):
         ########################################################
         lights.location[..., 2] = -2.0
         phong_shader = HardPhongShader(
-            lights=lights, cameras=cameras, materials=materials
+            lights=lights,
+            cameras=cameras,
+            materials=materials,
+            blend_params=blend_params,
         )
         phong_renderer = MeshRenderer(rasterizer=rasterizer, shader=phong_shader)
         images = phong_renderer(sphere_mesh, lights=lights)
@@ -162,6 +171,7 @@ class TestRenderMeshes(TestCaseMixin, unittest.TestCase):
         materials = Materials(device=device)
         lights = PointLights(device=device)
         lights.location = torch.tensor([0.0, 0.0, +2.0], device=device)[None]
+        blend_params = BlendParams(1e-4, 1e-4, (0, 0, 0))
 
         # Init renderer
         rasterizer = MeshRasterizer(cameras=cameras, raster_settings=raster_settings)
@@ -171,7 +181,12 @@ class TestRenderMeshes(TestCaseMixin, unittest.TestCase):
             "flat": HardFlatShader,
         }
         for (name, shader_init) in shaders.items():
-            shader = shader_init(lights=lights, cameras=cameras, materials=materials)
+            shader = shader_init(
+                lights=lights,
+                cameras=cameras,
+                materials=materials,
+                blend_params=blend_params,
+            )
             renderer = MeshRenderer(rasterizer=rasterizer, shader=shader)
             images = renderer(sphere_meshes)
             image_ref = load_rgb_image(