diff --git a/src/renderer/sw_engine/tvgSwRaster.cpp b/src/renderer/sw_engine/tvgSwRaster.cpp
index fd45ecb9..049318c7 100644
--- a/src/renderer/sw_engine/tvgSwRaster.cpp
+++ b/src/renderer/sw_engine/tvgSwRaster.cpp
@@ -257,8 +257,8 @@ static uint32_t _interpUpScaler(const uint32_t *img, TVG_UNUSED uint32_t stride,
     auto ry2 = ry + 1;
     if (ry2 >= h) ry2 = h - 1;
 
-    auto dx = static_cast<size_t>((sx - rx) * 255.0f);
-    auto dy = static_cast<size_t>((sy - ry) * 255.0f);
+    auto dx = static_cast<uint8_t>((sx - rx) * 255.0f);
+    auto dy = static_cast<uint8_t>((sy - ry) * 255.0f);
 
     auto c1 = img[rx + ry * w];
     auto c2 = img[rx2 + ry * w];
@@ -281,21 +281,23 @@ static uint32_t _interpDownScaler(const uint32_t *img, uint32_t stride, uint32_t
     int32_t maxx = (int32_t)sx + n;
     if (maxx >= (int32_t)w) maxx = w;
 
+    int32_t inc = (n / 2) + 1;
+    n = 0;
+
     auto src = img + minx + miny * stride;
 
-    for (auto y = miny; y < maxy; ++y) {
+    for (auto y = miny; y < maxy; y += inc) {
         auto p = src;
-        for (auto x = minx; x < maxx; ++x, ++p) {
-            c[0] += *p >> 24;
-            c[1] += (*p >> 16) & 0xff;
-            c[2] += (*p >> 8) & 0xff;
-            c[3] += *p & 0xff;
+        for (auto x = minx; x < maxx; x += inc, p += inc) {
+            c[0] += A(*p);
+            c[1] += C1(*p);
+            c[2] += C2(*p);
+            c[3] += C3(*p);
+            ++n;
         }
-        src += stride;
+        src += (stride * inc);
     }
 
-    n = (maxy - miny) * (maxx - minx);
-
     c[0] /= n;
     c[1] /= n;
     c[2] /= n;