Discussion:
[PATCH] Include physical resolution (pHYs section) in PNG output.
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Aaron Muir Hamilton
2017-04-16 09:06:48 UTC
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---
frontend/scanimage.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/frontend/scanimage.c b/frontend/scanimage.c
index 77c2288..432c2ea 100644
--- a/frontend/scanimage.c
+++ b/frontend/scanimage.c
@@ -1165,9 +1165,12 @@ write_pnm_header (SANE_Frame format, int width, int height, int depth, FILE *ofp

#ifdef HAVE_LIBPNG
static void
-write_png_header (SANE_Frame format, int width, int height, int depth, FILE *ofp, png_structp* png_ptr, png_infop* info_ptr)
+write_png_header (SANE_Frame format, int width, int height, int depth, int dpi, FILE *ofp, png_structp* png_ptr, png_infop* info_ptr)
{
int color_type;
+ /* PNG does not have imperial reference units, so we must convert to metric. */
+ /* There are nominally 39.3700787401575 inches in a meter. */
+ const double pixels_per_meter = dpi * 39.3700787401575;

*png_ptr = png_create_write_struct
(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
@@ -1200,6 +1203,10 @@ write_png_header (SANE_Frame format, int width, int height, int depth, FILE *ofp
depth, color_type, PNG_INTERLACE_NONE,
PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);

+ png_set_pHYs(*png_ptr, *info_ptr,
+ pixels_per_meter, pixels_per_meter,
+ PNG_RESOLUTION_METER);
+
png_write_info(*png_ptr, *info_ptr);
}
#endif
@@ -1379,7 +1386,8 @@ scan_it (FILE *ofp)
#ifdef HAVE_LIBPNG
case OUTPUT_PNG:
write_png_header (parm.format, parm.pixels_per_line,
- parm.lines, parm.depth, ofp, &png_ptr, &info_ptr);
+ parm.lines, parm.depth, resolution_value,
+ ofp, &png_ptr, &info_ptr);
break;
#endif
#ifdef HAVE_LIBJPEG
@@ -1635,7 +1643,8 @@ scan_it (FILE *ofp)
#ifdef HAVE_LIBPNG
case OUTPUT_PNG:
write_png_header (parm.format, parm.pixels_per_line,
- image.height, parm.depth, ofp, &png_ptr, &info_ptr);
+ image.height, parm.depth, resolution_value,
+ ofp, &png_ptr, &info_ptr);
break;
#endif
#ifdef HAVE_LIBJPEG
--
1.8.3.1
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