diff --git a/tsvm_core/src/net/torvald/tsvm/GraphicsJSR223Delegate.kt b/tsvm_core/src/net/torvald/tsvm/GraphicsJSR223Delegate.kt
index ed88b60..db64b7d 100644
--- a/tsvm_core/src/net/torvald/tsvm/GraphicsJSR223Delegate.kt
+++ b/tsvm_core/src/net/torvald/tsvm/GraphicsJSR223Delegate.kt
@@ -4729,6 +4729,11 @@ class GraphicsJSR223Delegate(private val vm: VM) {
                 }
             }
         }
+
+        // write Y=127 if there's no luma channel
+        if (channelLayout == CHANNEL_LAYOUT_COCG || channelLayout == CHANNEL_LAYOUT_COCG_A) {
+            Arrays.fill(finalYTile, 127f)
+        }
         
         // Convert to RGB based on TAV version and mode
         // v1,v3 = YCoCg-R, v2,v4 = ICtCp
@@ -5232,6 +5237,11 @@ class GraphicsJSR223Delegate(private val vm: VM) {
             }
         }
 
+        // write Y=127 if there's no luma channel
+        if (channelLayout == CHANNEL_LAYOUT_COCG || channelLayout == CHANNEL_LAYOUT_COCG_A) {
+            Arrays.fill(finalYTile, 127f)
+        }
+
         // Convert to RGB based on TAV version and mode
         // v1,v3 = YCoCg-R, v2,v4 = ICtCp
         if (tavVersion == 2 || tavVersion == 4) {