proc write_jpg_comment {file comment} {
set fh [open $file r+]
fconfigure $fh -encoding binary -translation binary -eofchar {}
if {[read $fh 2] != "\xFF\xD8"} { close $fh; return -code error "not a jpeg file" }
while {[read $fh 1] == "\xFF"} {
binary scan [read $fh 3] aS type len
set pos [tell $fh]
if {$type == "\xC0" } { set sof $pos; break }
if {$type == "\xFE"} { set com $pos; break }
seek $fh [expr {$pos + $len - 2}] start
}
set clen [binary format S [expr {[string length $comment] + 2}]]
if {[info exists com]} {
puts COM
seek $fh 0 start
set data1 [read $fh [expr {$com - 2}]]
binary scan [read $fh 2] S len
seek $fh [expr {$len - 2}] current
set data2 [read $fh]
close $fh
set fh [open $file w]
puts -nonewline $fh $data1$clen$comment$data2
} elseif {[info exists sof]} {
seek $fh [expr {$sof - 4}] start
set data [read $fh]
seek $fh [expr {$sof - 4}] start
puts -nonewline $fh "\xFF\xFE$clen$comment$data"
} else {
return -code error "no image found"
}
}--AF 19-12-03
See Also jpeg, Reading JPEG comments