add comments

git-svn-id: http://svn.code.sf.net/p/netpbm/code/trunk@3518 9d0c8265-081b-0410-96cb-a4ca84ce46f8

1 files changed, 5 insertions, 0 deletions

diff --git a/converter/other/pngx.c b/converter/other/pngx.c
index b96857e9..d900342f 100644
--- a/converter/other/pngx.c
+++ b/converter/other/pngx.c
@@ -475,6 +475,11 @@ pngx_setInterlaceHandling(struct pngx * const pngxP) {
 
        Also, documentation says this returns 7 if the compressor is
        interlacing, but it always returns 1 in practice.
+
+       If the program does 1 pass as directed by libpng, the image won't
+       decompress - libpng says "Not enough image data".  If the program does
+       7 passes as makes sense, the image won't decompress because "too many
+       IDAT's found."
     */
     pngxP->numPassesRequired = png_set_interlace_handling(pngxP->png_ptr);
 }