diff --git a/core/fxge/dib/cstretchengine.cpp b/core/fxge/dib/cstretchengine.cpp
index 4a851f8..e9629fc 100644
--- a/core/fxge/dib/cstretchengine.cpp
+++ b/core/fxge/dib/cstretchengine.cpp
@@ -197,6 +197,13 @@
       m_DestWidth(dest_width),
       m_DestHeight(dest_height),
       m_DestClip(clip_rect) {
+  if (m_bHasAlpha) {
+    DCHECK_EQ(m_DestFormat, FXDIB_Format::kArgb);
+    DCHECK_EQ(m_DestBpp, GetBppFromFormat(FXDIB_Format::kArgb));
+    DCHECK_EQ(m_pSource->GetFormat(), FXDIB_Format::kArgb);
+    DCHECK_EQ(m_SrcBpp, GetBppFromFormat(FXDIB_Format::kArgb));
+  }
+
   absl::optional<uint32_t> maybe_size =
       fxge::CalculatePitch32(m_DestBpp, clip_rect.Width());
   if (!maybe_size.has_value())
@@ -242,13 +249,8 @@
                                      : TransformMethod::k1BppToManyBpp;
       break;
     case 8:
-      if (m_DestBpp == 8) {
-        m_TransMethod = m_bHasAlpha ? TransformMethod::k8BppTo8BppWithAlpha
-                                    : TransformMethod::k8BppTo8Bpp;
-      } else {
-        m_TransMethod = m_bHasAlpha ? TransformMethod::k8BppToManyBppWithAlpha
-                                    : TransformMethod::k8BppToManyBpp;
-      }
+      m_TransMethod = m_DestBpp == 8 ? TransformMethod::k8BppTo8Bpp
+                                     : TransformMethod::k8BppToManyBpp;
       break;
     default:
       m_TransMethod = m_bHasAlpha ? TransformMethod::kManyBpptoManyBppWithAlpha
@@ -315,9 +317,6 @@
     pdfium::span<uint8_t> dest_span = m_InterBuf.writable_span().subspan(
         (m_CurRow - m_SrcClip.top) * m_InterPitch, m_InterPitch);
     size_t dest_span_index = 0;
-    // TODO(thestig): Audit suspicious variable usage.
-    const uint8_t* src_scan_mask = nullptr;
-    uint8_t* dest_scan_mask = nullptr;
     // TODO(npm): reduce duplicated code here
     switch (m_TransMethod) {
       case TransformMethod::k1BppTo8Bpp:
@@ -346,22 +345,6 @@
         }
         break;
       }
-      case TransformMethod::k8BppTo8BppWithAlpha: {
-        for (int col = m_DestClip.left; col < m_DestClip.right; ++col) {
-          PixelWeight* pWeights = m_WeightTable.GetPixelWeight(col);
-          uint32_t dest_a = 0;
-          uint32_t dest_r = 0;
-          for (int j = pWeights->m_SrcStart; j <= pWeights->m_SrcEnd; ++j) {
-            uint32_t pixel_weight = pWeights->GetWeightForPosition(j);
-            pixel_weight = pixel_weight * src_scan_mask[j] / 255;
-            dest_r += pixel_weight * src_scan[j];
-            dest_a += pixel_weight;
-          }
-          dest_span[dest_span_index++] = PixelFromFixed(dest_r);
-          *dest_scan_mask++ = PixelFromFixed(255 * dest_a);
-        }
-        break;
-      }
       case TransformMethod::k8BppToManyBpp: {
         for (int col = m_DestClip.left; col < m_DestClip.right; ++col) {
           PixelWeight* pWeights = m_WeightTable.GetPixelWeight(col);
@@ -387,29 +370,6 @@
         }
         break;
       }
-      case TransformMethod::k8BppToManyBppWithAlpha: {
-        for (int col = m_DestClip.left; col < m_DestClip.right; ++col) {
-          PixelWeight* pWeights = m_WeightTable.GetPixelWeight(col);
-          uint32_t dest_a = 0;
-          uint32_t dest_r = 0;
-          uint32_t dest_g = 0;
-          uint32_t dest_b = 0;
-          for (int j = pWeights->m_SrcStart; j <= pWeights->m_SrcEnd; ++j) {
-            uint32_t pixel_weight = pWeights->GetWeightForPosition(j);
-            pixel_weight = pixel_weight * src_scan_mask[j] / 255;
-            unsigned long argb = m_pSrcPalette[src_scan[j]];
-            dest_b += pixel_weight * static_cast<uint8_t>(argb >> 24);
-            dest_g += pixel_weight * static_cast<uint8_t>(argb >> 16);
-            dest_r += pixel_weight * static_cast<uint8_t>(argb >> 8);
-            dest_a += pixel_weight;
-          }
-          dest_span[dest_span_index++] = PixelFromFixed(dest_b);
-          dest_span[dest_span_index++] = PixelFromFixed(dest_g);
-          dest_span[dest_span_index++] = PixelFromFixed(dest_r);
-          *dest_scan_mask++ = PixelFromFixed(255 * dest_a);
-        }
-        break;
-      }
       case TransformMethod::kManyBpptoManyBpp: {
         for (int col = m_DestClip.left; col < m_DestClip.right; ++col) {
           PixelWeight* pWeights = m_WeightTable.GetPixelWeight(col);
@@ -431,6 +391,7 @@
         break;
       }
       case TransformMethod::kManyBpptoManyBppWithAlpha: {
+        DCHECK(m_bHasAlpha);
         for (int col = m_DestClip.left; col < m_DestClip.right; ++col) {
           PixelWeight* pWeights = m_WeightTable.GetPixelWeight(col);
           uint32_t dest_a = 0;
@@ -438,13 +399,9 @@
           uint32_t dest_g = 0;
           uint32_t dest_b = 0;
           for (int j = pWeights->m_SrcStart; j <= pWeights->m_SrcEnd; ++j) {
-            uint32_t pixel_weight = pWeights->GetWeightForPosition(j);
             const uint8_t* src_pixel = src_scan + j * Bpp;
-            if (m_DestFormat == FXDIB_Format::kArgb) {
-              pixel_weight = pixel_weight * src_pixel[3] / 255;
-            } else {
-              pixel_weight = pixel_weight * src_scan_mask[j] / 255;
-            }
+            uint32_t pixel_weight =
+                pWeights->GetWeightForPosition(j) * src_pixel[3] / 255;
             dest_b += pixel_weight * (*src_pixel++);
             dest_g += pixel_weight * (*src_pixel++);
             dest_r += pixel_weight * (*src_pixel);
@@ -453,10 +410,7 @@
           dest_span[dest_span_index++] = PixelFromFixed(dest_b);
           dest_span[dest_span_index++] = PixelFromFixed(dest_g);
           dest_span[dest_span_index++] = PixelFromFixed(dest_r);
-          if (m_DestFormat == FXDIB_Format::kArgb)
-            dest_span[dest_span_index] = PixelFromFixed(255 * dest_a);
-          if (dest_scan_mask)
-            *dest_scan_mask++ = PixelFromFixed(255 * dest_a);
+          dest_span[dest_span_index] = PixelFromFixed(255 * dest_a);
           dest_span_index += Bpp - 3;
         }
         break;
@@ -481,8 +435,6 @@
   const int DestBpp = m_DestBpp / 8;
   for (int row = m_DestClip.top; row < m_DestClip.bottom; ++row) {
     unsigned char* dest_scan = m_DestScanline.data();
-    // TODO(thestig): Audit suspicious variable usage.
-    unsigned char* dest_scan_mask = nullptr;
     PixelWeight* pWeights = table.GetPixelWeight(row);
     switch (m_TransMethod) {
       case TransformMethod::k1BppTo8Bpp:
@@ -502,28 +454,6 @@
         }
         break;
       }
-      case TransformMethod::k8BppTo8BppWithAlpha: {
-        for (int col = m_DestClip.left; col < m_DestClip.right; ++col) {
-          pdfium::span<const uint8_t> src_span =
-              m_InterBuf.span().subspan((col - m_DestClip.left) * DestBpp);
-          // TODO(thestig): Audit suspicious variable usage.
-          unsigned char* src_scan_mask =
-              reinterpret_cast<unsigned char*>(col - m_DestClip.left);
-          uint32_t dest_a = 0;
-          uint32_t dest_k = 0;
-          for (int j = pWeights->m_SrcStart; j <= pWeights->m_SrcEnd; ++j) {
-            uint32_t pixel_weight = pWeights->GetWeightForPosition(j);
-            dest_k +=
-                pixel_weight * src_span[(j - m_SrcClip.top) * m_InterPitch];
-            dest_a += pixel_weight *
-                      src_scan_mask[(j - m_SrcClip.top) * m_ExtraMaskPitch];
-          }
-          *dest_scan = PixelFromFixed(dest_k);
-          dest_scan += DestBpp;
-          *dest_scan_mask++ = PixelFromFixed(dest_a);
-        }
-        break;
-      }
       case TransformMethod::k8BppToManyBpp:
       case TransformMethod::kManyBpptoManyBpp: {
         for (int col = m_DestClip.left; col < m_DestClip.right; ++col) {
@@ -547,37 +477,24 @@
         }
         break;
       }
-      case TransformMethod::k8BppToManyBppWithAlpha:
       case TransformMethod::kManyBpptoManyBppWithAlpha: {
+        DCHECK(m_bHasAlpha);
         for (int col = m_DestClip.left; col < m_DestClip.right; ++col) {
           pdfium::span<const uint8_t> src_span =
               m_InterBuf.span().subspan((col - m_DestClip.left) * DestBpp);
-          // TODO(thestig): Audit suspicious variable usage.
-          unsigned char* src_scan_mask = nullptr;
-          if (m_DestFormat != FXDIB_Format::kArgb) {
-            src_scan_mask =
-                reinterpret_cast<unsigned char*>(col - m_DestClip.left);
-          }
           uint32_t dest_a = 0;
           uint32_t dest_r = 0;
           uint32_t dest_g = 0;
           uint32_t dest_b = 0;
-          const size_t pixel_bytes =
-              m_DestFormat == FXDIB_Format::kArgb ? 4 : 3;
+          constexpr size_t kPixelBytes = 4;
           for (int j = pWeights->m_SrcStart; j <= pWeights->m_SrcEnd; ++j) {
             uint32_t pixel_weight = pWeights->GetWeightForPosition(j);
             pdfium::span<const uint8_t> src_pixel = src_span.subspan(
-                (j - m_SrcClip.top) * m_InterPitch, pixel_bytes);
-            int mask_v = 255;
-            if (src_scan_mask)
-              mask_v = src_scan_mask[(j - m_SrcClip.top) * m_ExtraMaskPitch];
+                (j - m_SrcClip.top) * m_InterPitch, kPixelBytes);
             dest_b += pixel_weight * src_pixel[0];
             dest_g += pixel_weight * src_pixel[1];
             dest_r += pixel_weight * src_pixel[2];
-            if (m_DestFormat == FXDIB_Format::kArgb)
-              dest_a += pixel_weight * src_pixel[3];
-            else
-              dest_a += pixel_weight * mask_v;
+            dest_a += pixel_weight * src_pixel[3];
           }
           if (dest_a) {
             int r = static_cast<uint32_t>(dest_r) * 255 / dest_a;
@@ -587,13 +504,8 @@
             dest_scan[1] = pdfium::clamp(g, 0, 255);
             dest_scan[2] = pdfium::clamp(r, 0, 255);
           }
-          if (m_DestFormat == FXDIB_Format::kArgb)
-            dest_scan[3] = PixelFromFixed(dest_a);
-          else
-            *dest_scan_mask = PixelFromFixed(dest_a);
+          dest_scan[3] = PixelFromFixed(dest_a);
           dest_scan += DestBpp;
-          if (dest_scan_mask)
-            dest_scan_mask++;
         }
         break;
       }
diff --git a/core/fxge/dib/cstretchengine.h b/core/fxge/dib/cstretchengine.h
index 6dabcb1..2ee1477 100644
--- a/core/fxge/dib/cstretchengine.h
+++ b/core/fxge/dib/cstretchengine.h
@@ -132,9 +132,7 @@
     k1BppTo8Bpp,
     k1BppToManyBpp,
     k8BppTo8Bpp,
-    k8BppTo8BppWithAlpha,
     k8BppToManyBpp,
-    k8BppToManyBppWithAlpha,
     kManyBpptoManyBpp,
     kManyBpptoManyBppWithAlpha
   };