diff --git a/core/fpdfapi/render/cpdf_imagerenderer.cpp b/core/fpdfapi/render/cpdf_imagerenderer.cpp
index aa2038a..c5f3f1d 100644
--- a/core/fpdfapi/render/cpdf_imagerenderer.cpp
+++ b/core/fpdfapi/render/cpdf_imagerenderer.cpp
@@ -313,7 +313,6 @@
                              nullptr)) {
     return true;
   }
-  bitmap_device1.GetBitmap()->Clear(0);
 
   CPDF_RenderStatus bitmap_render(m_pRenderStatus->GetContext(),
                                   &bitmap_device1);
@@ -339,7 +338,6 @@
                              FXDIB_Format::k8bppRgb, nullptr)) {
     return true;
   }
-  bitmap_device2.GetBitmap()->Clear(0);
   CalculateDrawImage(&bitmap_device1, &bitmap_device2, m_pDIBBase, new_matrix,
                      rect);
   bitmap_device2.GetBitmap()->ConvertFormat(FXDIB_Format::k8bppMask);
@@ -381,7 +379,6 @@
                              FXDIB_Format::k8bppRgb, nullptr)) {
     return true;
   }
-  ClearBitmap(bitmap_device2, 0);
   CalculateDrawImage(&bitmap_device1, &bitmap_device2, m_pLoader->GetMask(),
                      new_matrix, rect);
 #if defined(_SKIA_SUPPORT_)
diff --git a/core/fpdfapi/render/cpdf_rendershading.cpp b/core/fpdfapi/render/cpdf_rendershading.cpp
index 5228a70..ce7543b 100644
--- a/core/fpdfapi/render/cpdf_rendershading.cpp
+++ b/core/fpdfapi/render/cpdf_rendershading.cpp
@@ -921,7 +921,9 @@
   if (pBitmap->GetBuffer().empty())
     return;
 
-  pBitmap->Clear(background);
+  if (background != 0) {
+    pBitmap->Clear(background);
+  }
   const CFX_Matrix final_matrix = mtMatrix * buffer.GetMatrix();
   const auto& funcs = pPattern->GetFuncs();
   switch (pPattern->GetShadingType()) {
diff --git a/core/fpdfapi/render/cpdf_renderstatus.cpp b/core/fpdfapi/render/cpdf_renderstatus.cpp
index 3eac569..fe58de8 100644
--- a/core/fpdfapi/render/cpdf_renderstatus.cpp
+++ b/core/fpdfapi/render/cpdf_renderstatus.cpp
@@ -725,7 +725,9 @@
   }
   CFX_Matrix FinalMatrix = m_DeviceMatrix;
   FinalMatrix.Translate(-bbox.left, -bbox.top);
-  pBackdrop->Clear(pBackdrop->IsAlphaFormat() ? 0 : 0xffffffff);
+  if (!pBackdrop->IsAlphaFormat()) {
+    pBackdrop->Clear(0xffffffff);
+  }
 
   CFX_DefaultRenderDevice device;
   device.Attach(pBackdrop);
diff --git a/core/fpdfapi/render/cpdf_rendertiling.cpp b/core/fpdfapi/render/cpdf_rendertiling.cpp
index db1f338..fcde2b2 100644
--- a/core/fpdfapi/render/cpdf_rendertiling.cpp
+++ b/core/fpdfapi/render/cpdf_rendertiling.cpp
@@ -39,7 +39,6 @@
   CFX_DefaultRenderDevice bitmap_device;
   bitmap_device.AttachWithBackdropAndGroupKnockout(
       pBitmap, /*pBackdropBitmap=*/nullptr, /*bGroupKnockout=*/true);
-  pBitmap->Clear(0);
   CFX_FloatRect cell_bbox =
       pPattern->pattern_to_form().TransformRect(pPattern->bbox());
   cell_bbox = mtObject2Device.TransformRect(cell_bbox);
@@ -195,7 +194,6 @@
   if (!pScreen->Create(clip_width, clip_height, FXDIB_Format::kArgb))
     return nullptr;
 
-  pScreen->Clear(0);
   pdfium::span<const uint8_t> src_buf = pPatternBitmap->GetBuffer();
   for (int col = min_col; col <= max_col; col++) {
     for (int row = min_row; row <= max_row; row++) {
diff --git a/core/fxge/agg/fx_agg_driver.cpp b/core/fxge/agg/fx_agg_driver.cpp
index 19b46ff..a1949de 100644
--- a/core/fxge/agg/fx_agg_driver.cpp
+++ b/core/fxge/agg/fx_agg_driver.cpp
@@ -1054,7 +1054,6 @@
   auto pThisLayer = pdfium::MakeRetain<CFX_DIBitmap>();
   pThisLayer->Create(path_rect.Width(), path_rect.Height(),
                      FXDIB_Format::k8bppMask);
-  pThisLayer->Clear(0);
   agg::rendering_buffer raw_buf(pThisLayer->GetBuffer().data(),
                                 pThisLayer->GetWidth(), pThisLayer->GetHeight(),
                                 pThisLayer->GetPitch());
diff --git a/core/fxge/cfx_renderdevice.cpp b/core/fxge/cfx_renderdevice.cpp
index 7e178ce..d39a02f 100644
--- a/core/fxge/cfx_renderdevice.cpp
+++ b/core/fxge/cfx_renderdevice.cpp
@@ -767,7 +767,6 @@
     return false;
 
   if (bitmap->IsAlphaFormat()) {
-    bitmap->Clear(0);
     backdrop->Copy(bitmap);
   } else {
     if (!m_pDeviceDriver->GetDIBits(bitmap, rect.left, rect.top))
@@ -1115,7 +1114,6 @@
     auto bitmap = pdfium::MakeRetain<CFX_DIBitmap>();
     if (!bitmap->Create(pixel_width, pixel_height, FXDIB_Format::k1bppMask))
       return false;
-    bitmap->Clear(0);
     for (const TextGlyphPos& glyph : glyphs) {
       if (!glyph.m_pGlyph)
         continue;
@@ -1144,8 +1142,6 @@
     bitmap->Clear(0xFFFFFFFF);
     if (!GetDIBits(bitmap, bmp_rect.left, bmp_rect.top))
       return false;
-  } else {
-    bitmap->Clear(0);
   }
   int dest_width = pixel_width;
   int a = 0;
diff --git a/core/fxge/dib/cfx_dibitmap.cpp b/core/fxge/dib/cfx_dibitmap.cpp
index fff3977..62881a6 100644
--- a/core/fxge/dib/cfx_dibitmap.cpp
+++ b/core/fxge/dib/cfx_dibitmap.cpp
@@ -167,6 +167,8 @@
     case FXDIB_Format::kArgb: {
       if (CFX_DefaultRenderDevice::SkiaIsDefaultRenderer() &&
           FXDIB_Format::kRgb32 == GetFormat()) {
+        // TODO(crbug.com/pdfium/2016): This is not reliable because alpha may
+        // be modified outside of this operation.
         color |= 0xFF000000;
       }
       for (int i = 0; i < m_Width; i++)
diff --git a/core/fxge/dib/cfx_imagetransformer.cpp b/core/fxge/dib/cfx_imagetransformer.cpp
index af4c35d..904a7f5 100644
--- a/core/fxge/dib/cfx_imagetransformer.cpp
+++ b/core/fxge/dib/cfx_imagetransformer.cpp
@@ -246,8 +246,6 @@
   if (!pTransformed->Create(m_result.Width(), m_result.Height(), format))
     return;
 
-  pTransformed->Clear(0);
-
   CFX_Matrix result2stretch(1.0f, 0.0f, 0.0f, 1.0f, m_result.left,
                             m_result.top);
   result2stretch.Concat(m_dest2stretch);
diff --git a/core/fxge/win32/cfx_psrenderer_unittest.cpp b/core/fxge/win32/cfx_psrenderer_unittest.cpp
index 81430df..6186f0f 100644
--- a/core/fxge/win32/cfx_psrenderer_unittest.cpp
+++ b/core/fxge/win32/cfx_psrenderer_unittest.cpp
@@ -204,7 +204,6 @@
     auto bitmap = pdfium::MakeRetain<CFX_DIBitmap>();
     bool result = bitmap->Create(kWidth, kHeight, FXDIB_Format::k1bppRgb);
     ASSERT_TRUE(result);
-    bitmap->Clear(0);
     ASSERT_TRUE(renderer.DrawDIBits(bitmap, /*color=*/0, CFX_Matrix(),
                                     FXDIB_ResampleOptions()));
   }