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Bilinear interpolation: Difference between revisions
Tcl implementation added
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(flomap-bilinear-ref
fm k (+ 1/2 (/ x 250)) (+ 1/2 (/ y 250))))))</lang>
=={{header|Tcl}}==
This uses the polynomial expansion described in wikipedia, and draws the same example as illustrated in that page with a different pallette. It's not particularly fast - about 300ms for a 200x200 surface on an arbitrary machine.
The script below will show the computed image in a GUI frame, and present a button to save it.
<lang Tcl>
package require Tk
proc pixel {f} {
if {$f < 0} {
error "why is $f?"
}
set i [expr {0xff & entier(0xff*$f)}]
format #%02x%02x%02x $i [expr {255-$i}] 127
}
proc bilerp {im O X Y XY} {
set w [image width $im]
set h [image height $im]
set dx [expr {1.0/$w}]
set dy [expr {1.0/$h}]
set a0 $O
set a1 [expr {$X - $O}]
set a2 [expr {$Y - $O}]
set a3 [expr {$O + $XY - ($X + $Y)}]
for {set y 0} {$y < $h} {incr y} {
for {set x 0} {$x < $w} {incr x} {
set i [expr {$x * $dx}]
set j [expr {$y * $dy}]
set xv [expr {$a0 + $a1*$i + $a2*$j + $a3*$i*$j}]
set y [expr {$h - $y}] ;# invert for screen coords
$im put [pixel $xv] -to $x $y
}
}
}
proc save {im} {
set fn [tk_getSaveFile -defaultextension png]
if {$fn eq ""} return
set fd [open $fn wb]
puts -nonewline $fd [$im data -format png]
close $fd
tk_messageBox -message "Saved as $fn!"
}
set im [image create photo -width 200 -height 200]
puts [time {bilerp $im 0 1 1 0.5} 1]
pack [label .l1 -image $im]
pack [button .b -text "save" -command [list save $im]]
</lang>
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