https://github.com/ImageMagick/ImageMagick/issues/1343

diff --git a/coders/png.c b/coders/png.c
index 6ff2ece78f7130d6e84434dee5069341d0a5ee10..b1cf32259a215198ddddb865a182b10d98a3d436 100644 (file)
--- a/coders/png.c
+++ b/coders/png.c
@@ -8923,7 +8923,8 @@ static MagickBooleanType WriteOnePNGImage(MngInfo *mng_info,
   tried_333 = MagickFalse;
   tried_444 = MagickFalse;
 
-  image->depth=GetImageDepth(image,exception);
+  if (image->depth != GetImageDepth(image,exception))
+    (void) SetImageDepth(image,image->depth,exception);
   for (j=0; j<6; j++)
   {
     /*