diff -urN netpbm-10.70.00-orig/converter/other/pamrgbatopng.c netpbm-10.70.00/converter/other/pamrgbatopng.c
--- netpbm-10.70.00-orig/converter/other/pamrgbatopng.c	2013-07-25 11:51:11 +0900
+++ netpbm-10.70.00/converter/other/pamrgbatopng.c	2015-12-26 13:05:48 +0900
@@ -1,5 +1,6 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include <zlib.h>
 /* Because of poor design of libpng, you must not #include <setjmp.h> before
 <png.h>.  Compile failure results.
 */
@@ -90,6 +91,8 @@
 
     pngx_create(&pngxP, PNGX_WRITE, NULL);
     
+    png_set_compression_level(pngxP->png_ptr, Z_BEST_COMPRESSION);
+
     pngx_setIhdr(pngxP, pamP->width, pamP->height,
                  8, PNG_COLOR_TYPE_RGB_ALPHA, 0, 0, 0);