Also check if `image_info->compression` is set.

diff --git a/coders/png.c b/coders/png.c
index 68aa0a934226aa518917a315095f02e0897f3cf4..9e4d408b7d952d44642d30f29ee2eaa8da8a79f0 100644 (file)
--- a/coders/png.c
+++ b/coders/png.c
@@ -12735,7 +12735,8 @@ static MagickBooleanType WriteOneJNGImage(MngInfo *mng_info,
 
   jng_quality=image_info->quality == 0UL ? 75UL : image_info->quality%1000;
 
-  jng_alpha_compression_method=image->compression==JPEGCompression? 8 : 0;
+  jng_alpha_compression_method=(image->compression==JPEGCompression ||
+    image_info->compression==JPEGCompression) ? 8 : 0;
 
   jng_alpha_quality=image_info->quality == 0UL ? 75UL :
       image_info->quality;