diff --git a/core/fpdfapi/page/cpdf_colorspace.cpp b/core/fpdfapi/page/cpdf_colorspace.cpp
index d458d5e..fafeaf4 100644
--- a/core/fpdfapi/page/cpdf_colorspace.cpp
+++ b/core/fpdfapi/page/cpdf_colorspace.cpp
@@ -653,6 +653,10 @@
                                          int image_width,
                                          int image_height,
                                          bool bTransMask) const {
+  // Only applies to CMYK colorspaces. None of the colorspaces that use this
+  // generic base implementation are CMYK.
+  CHECK(!bTransMask);
+
   uint8_t* dest_buf = dest_span.data();
   const uint8_t* src_buf = src_span.data();
   std::vector<float> src(m_nComponents);
@@ -738,6 +742,8 @@
                                       int image_width,
                                       int image_height,
                                       bool bTransMask) const {
+  CHECK(!bTransMask);  // Only applies to CMYK colorspaces.
+
   uint8_t* pDestBuf = dest_span.data();
   const uint8_t* pSrcBuf = src_span.data();
   for (int i = 0; i < pixels; i++) {
@@ -817,28 +823,11 @@
                                      int image_width,
                                      int image_height,
                                      bool bTransMask) const {
+  CHECK(!bTransMask);  // Only applies to CMYK colorspaces.
+
   uint8_t* pDestBuf = dest_span.data();
   const uint8_t* pSrcBuf = src_span.data();
-  if (!bTransMask) {
-    fxcodec::ReverseRGB(pDestBuf, pSrcBuf, pixels);
-    return;
-  }
-
-  float Cal[3];
-  float R;
-  float G;
-  float B;
-  for (int i = 0; i < pixels; i++) {
-    Cal[0] = static_cast<float>(pSrcBuf[2]) / 255;
-    Cal[1] = static_cast<float>(pSrcBuf[1]) / 255;
-    Cal[2] = static_cast<float>(pSrcBuf[0]) / 255;
-    GetRGB(Cal, &R, &G, &B);
-    pDestBuf[0] = FXSYS_roundf(B * 255);
-    pDestBuf[1] = FXSYS_roundf(G * 255);
-    pDestBuf[2] = FXSYS_roundf(R * 255);
-    pSrcBuf += 3;
-    pDestBuf += 3;
-  }
+  fxcodec::ReverseRGB(pDestBuf, pSrcBuf, pixels);
 }
 
 CPDF_LabCS::CPDF_LabCS() : CPDF_ColorSpace(Family::kLab) {}
@@ -925,6 +914,8 @@
                                     int image_width,
                                     int image_height,
                                     bool bTransMask) const {
+  CHECK(!bTransMask);  // Only applies to CMYK colorspaces.
+
   uint8_t* pDestBuf = dest_span.data();
   const uint8_t* pSrcBuf = src_span.data();
   for (int i = 0; i < pixels; i++) {
@@ -1022,6 +1013,8 @@
                                          int image_width,
                                          int image_height,
                                          bool bTransMask) const {
+  CHECK(!bTransMask);  // Only applies to CMYK colorspaces.
+
   if (profile_->IsSRGB()) {
     fxcodec::ReverseRGB(dest_span.data(), src_span.data(), pixels);
     return;
diff --git a/core/fpdfapi/page/cpdf_colorspace_unittest.cpp b/core/fpdfapi/page/cpdf_colorspace_unittest.cpp
index d0196fe..759490d 100644
--- a/core/fpdfapi/page/cpdf_colorspace_unittest.cpp
+++ b/core/fpdfapi/page/cpdf_colorspace_unittest.cpp
@@ -19,20 +19,14 @@
 
   uint8_t dst[12];
   memset(dst, 0xbd, sizeof(dst));
-  pCal->TranslateImageLine(dst, kSrc, 4, 4, 1, true);
-  for (size_t i = 0; i < 12; ++i)
-    EXPECT_EQ(dst[i], kExpect[i]) << " at " << i;
-
-  memset(dst, 0xbd, sizeof(dst));
-  pCal->TranslateImageLine(dst, kSrc, 4, 4, 1, false);
+  // `bTransMask` only applies to CYMK colorspaces.
+  pCal->TranslateImageLine(dst, kSrc, 4, 4, 1, /*bTransMask=*/false);
   for (size_t i = 0; i < 12; ++i)
     EXPECT_EQ(dst[i], kExpect[i]) << " at " << i;
 }
 
 TEST(CPDF_CalRGB, TranslateImageLine) {
   const uint8_t kSrc[12] = {255, 0, 0, 0, 255, 0, 0, 0, 255, 128, 128, 128};
-  const uint8_t kExpectMask[12] = {255, 58, 0,   0,   255, 0,
-                                   70,  0,  255, 188, 188, 188};
   const uint8_t kExpectNomask[12] = {0,   0, 255, 0,   255, 0,
                                      255, 0, 0,   128, 128, 128};
 
@@ -41,12 +35,8 @@
 
   uint8_t dst[12];
   memset(dst, 0xbd, sizeof(dst));
-  pCal->TranslateImageLine(dst, kSrc, 4, 4, 1, true);
-  for (size_t i = 0; i < 12; ++i)
-    EXPECT_EQ(dst[i], kExpectMask[i]) << " at " << i;
-
-  memset(dst, 0xbd, sizeof(dst));
-  pCal->TranslateImageLine(dst, kSrc, 4, 4, 1, false);
+  // `bTransMask` only applies to CYMK colorspaces.
+  pCal->TranslateImageLine(dst, kSrc, 4, 4, 1, /*bTransMask=*/false);
   for (size_t i = 0; i < 12; ++i)
     EXPECT_EQ(dst[i], kExpectNomask[i]) << " at " << i;
 }
diff --git a/core/fpdfapi/page/cpdf_devicecs.cpp b/core/fpdfapi/page/cpdf_devicecs.cpp
index 6daffb8..d152938 100644
--- a/core/fpdfapi/page/cpdf_devicecs.cpp
+++ b/core/fpdfapi/page/cpdf_devicecs.cpp
@@ -84,6 +84,8 @@
   const uint8_t* pSrcBuf = src_span.data();
   switch (GetFamily()) {
     case Family::kDeviceGray:
+      CHECK(!bTransMask);  // Only applies to CMYK colorspaces.
+
       for (int i = 0; i < pixels; i++) {
         // Compiler can not conclude that src/dest don't overlap, avoid
         // duplicate loads.
@@ -94,6 +96,8 @@
       }
       break;
     case Family::kDeviceRGB:
+      CHECK(!bTransMask);  // Only applies to CMYK colorspaces.
+
       fxcodec::ReverseRGB(pDestBuf, pSrcBuf, pixels);
       break;
     case Family::kDeviceCMYK: