Index: modules/png/ChangeLog
==================================================================
--- modules/png/ChangeLog
+++ modules/png/ChangeLog
@@ -1,5 +1,9 @@
+2018-12-12  Harald Oehlmann <oehhar@users.sourceforge.net>
+
+	* png.tcl: add function getPixelDimension to   get physical pixel size
+
 2013-02-01  Andreas Kupries  <andreas_kupries@users.sourceforge.net>
 
 	*
 	* Released and tagged Tcllib 1.15 ========================
 	* 

Index: modules/png/pkgIndex.tcl
==================================================================
--- modules/png/pkgIndex.tcl
+++ modules/png/pkgIndex.tcl
@@ -1,2 +1,2 @@
 if {![package vsatisfies [package provide Tcl] 8.2]} {return}
-package ifneeded png 0.2 [list source [file join $dir png.tcl]]
+package ifneeded png 0.3 [list source [file join $dir png.tcl]]

Index: modules/png/png.man
==================================================================
--- modules/png/png.man
+++ modules/png/png.man
@@ -1,6 +1,7 @@
-[manpage_begin png n 0.1.2]
+[vset VERSION 0.3]
+[manpage_begin png n [vset VERSION]]
 [keywords comment]
 [keywords image]
 [keywords png]
 [keywords timestamp]
 [copyright {2004, Code: Aaron Faupell <afaupell@users.sourceforge.net>}]
@@ -8,11 +9,11 @@
 [moddesc   {Image manipulation}]
 [titledesc {PNG querying and manipulation of meta data}]
 [category  {File formats}]
 [require Tcl 8.2]
 [require crc32]
-[require png [opt 0.1.2]]
+[require png [opt [vset VERSION]]]
 [description]
 [para]
 
 This package provides commands to query and modify PNG images. PNG
 stands for [term {Portable Network Graphics}] and is specified at
@@ -123,10 +124,23 @@
 is found. [arg keyword] has to be less than 80 characters long to
 conform to the PNG specification. [arg keyword2] is the translated
 [arg keyword], in the language specified by the language identifier
 [arg lang].
 
+[call [cmd ::png::getPixelDimension] [arg file]]
+
+Returns a dictionary with keys [const ppux], [const ppuy] and
+[const unit] if the information is present.  Otherwise, it returns the empty
+string.
+
+[para] The values of [const ppux] and [const ppuy] return the pixel
+per unit value in X or Y direction.
+
+[para] The allowed values for key [const unit] are [const meter] and
+[const unknown]. In the case of meter, the dpi value can be calculated
+by multiplying with the conversion factor [const 0.0254].
+
 [call [cmd ::png::image] [arg file]]
 
 Given a PNG file returns the image in the list of scanlines format used by Tk_GetColor.
 
 [call [cmd ::png::write] [arg file] [arg data]]

Index: modules/png/png.tcl
==================================================================
--- modules/png/png.tcl
+++ modules/png/png.tcl
@@ -7,11 +7,11 @@
 # See the file "license.terms" for information on usage and redistribution
 # of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 # 
 # RCS: @(#) $Id: png.tcl,v 1.11 2012/07/09 16:35:04 afaupell Exp $
 
-package provide png 0.2
+package provide png 0.3
 
 namespace eval ::png {}
 
 proc ::png::_openPNG {file {mode r}} {
     set fh [open $file $mode]
@@ -207,10 +207,32 @@
         seek $fh [expr {$len + 4}] current
     }
     close $fh
     return -code error "no data chunk found"
 }
+
+proc ::png::getPixelDimension {file} {
+    set fh [_openPNG $file]
+
+    while {[set r [read $fh 8]] != ""} {
+        binary scan $r Ia4 len type
+        if {$type == "pHYs"} {
+            set r [read $fh [expr {$len + 4}]]
+            binary scan $r IIc ppux ppuy unit
+            close $fh
+            # mask out sign bit, from tcl 8.5, one may use u specifier
+            set res [list ppux [expr {$ppux & 0xFFFFFFFF}]\
+                     ppuy [expr {$ppuy & 0xFFFFFFFF}]\
+                    unit]
+            if {$unit == 1} {lappend res meter} else {lappend res unknown}
+            return $res
+        }
+        seek $fh [expr {$len + 4}] current
+    }
+    close $fh
+    return
+}
 
 proc ::png::image {file} {
     set fh [_openPNG $file]
     set chunks [_chunks $fh]
     set cdata {}

Index: modules/png/png.test
==================================================================
--- modules/png/png.test
+++ modules/png/png.test
@@ -299,8 +299,23 @@
 	set res [list [::png::validate $copy] [::png::getComments $copy]]
 	removeFile pngrc.$root
 	set res
     } {OK {}}
 }
+
+# -------------------------------------------------------------------------
+# PhysicalDimensions
+
+test png-physical-dimensions-missing {Test for empty list if no physical dimensions present} {
+    ::png::getPixelDimension [file join\
+	    [file dirname [file join [pwd] [info script]]]\
+	    testimages/physicaldimensions/basi0g01.png]
+} {}
+
+test png-physical-dimensions-missing {Test for empty list if no physical dimensions present} {
+    ::png::getPixelDimension [file join\
+	    [file dirname [file join [pwd] [info script]]]\
+	    testimages/physicaldimensions/basi0g01_300dpi.png]
+} {ppux 11811 ppuy 11811 unit meter}
 
 # -------------------------------------------------------------------------
 testsuiteCleanup

ADDED   modules/png/testimages/physicaldimensions/basi0g01.png
Index: modules/png/testimages/physicaldimensions/basi0g01.png
==================================================================
--- /dev/null
+++ modules/png/testimages/physicaldimensions/basi0g01.png
cannot compute difference between binary files

ADDED   modules/png/testimages/physicaldimensions/basi0g01_300dpi.png
Index: modules/png/testimages/physicaldimensions/basi0g01_300dpi.png
==================================================================
--- /dev/null
+++ modules/png/testimages/physicaldimensions/basi0g01_300dpi.png
cannot compute difference between binary files