[LyX/2.5.x] Fix PDF->PNG conversion problem on MacOS (#12632)

[Koji Yokota]

commit 943439c9ff6f79d48e01931d18babeeefb3fb5c9
Author: Koji Yokota <yokota at lyx.org>
Date:   Fri Feb 27 08:59:03 2026 +0900

    Fix PDF->PNG conversion problem on MacOS (#12632)
---
 lib/configure.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/lib/configure.py b/lib/configure.py
index d49ec078f1..28133a9a6a 100644
--- a/lib/configure.py
+++ b/lib/configure.py
@@ -1147,7 +1147,11 @@ def checkConverterEntries():
         rc_entry = [ r'\converter eps        pdf6       "epstopdf --outfile=$$o $$i"	""'])
     #
     #prepare for pdf -> png, 2nd part depends on IM ban below
-    pdftopng = ['sips --resampleWidth 800 --setProperty format png $$i --out $$o' ]
+    if sys.platform == 'darwin':
+        pdftopng = ['gs -sDEVICE=pngalpha -r200 -dUseCropBox -o $$o $$i',
+                    'sips --resampleWidth 800 --setProperty format png $$i --out $$o']
+    else:
+        pdftopng = []
     #
     # Due to more restrictive policies, it is possible that (image)magick
     # does not allow conversions from eps to png.