and the anwer is:
package require Tk
image create photo preview -file preview.pnm
ttk::frame .c
ttk::label .c.preview -image preview
grid .c -column 0 -row 0 -sticky nwes
grid .c.preview -column 0 -row 0
grid columnconfigure . 0 -weight 1
grid rowconfigure . 0 -weight 1
grid columnconfigure .c 0 -weight 1
grid rowconfigure .c 0 -weight 1
bind .c.preview <Configure> {
exec convert preview.pnm -resize %wx%h -background lightgray -gravity center -extent %wx%h newfile
preview read newfile -shrink
}