TD-e.com

Correct horizon

A script-fu for The Gimp

Example

Image 1: Using the rectangular selection tool, we define 2 points on the slanted line.

Before calling the Skript-fu, a rectangualr selection must be set

Image 2: Correction executed
Image corrected with the Skript-fu 'Correct horizon'

Description

"Correct horizon" is a script-fu for the Gimp. It is an enhanced version of the script "Crop rotated photos". "Correct horizon" also performs the rotation needed to correct a slanted horizon or even a slanted vertical axis. There is no more need to guess by which angle you must rotate your photo. Just define two points on the line that should be horizontal or vertical and run the script.

For more details, read the tutorial with examples.

The script has been tested with The Gimp version 2.2.9 on Linux SuSE and with The Gimp version 2.2.10 on Windoze.
The script version 1.10 has been tested with The Gimp version 2.4.0 on Linux Ubuntu 7.10 Gutsy Gibbon.
The script version 1.13 has been tested with The Gimp version 2.6.8 on Linux Ubuntu 10.04 Lucid Lynx.

Versions

2011.07.10 : The current version is 1.13. It has been tested with Gimp 2.6.8. Manual angle and anti-clock rotation did not worrk any more lately. Problem corrected.
2007.10.24 : The version 1.10 has been adapted to The Gimp 2.4.

Download:

Click into the blue frame below where the script is listed.
Type Control-A to select the complete text of the script.
Type Control-C to copy the script to the clipboard.
Go to your text editor (gedit, Kate, Aedix, Notepad, etc) and type Control-V to paste the script.
Save it as a file named correct-horizon.scm

Linux Ubuntu or other Gnome:   use the text editor gedit or bluefish

Linux Kubuntu or other KDE:   use the text editor Kate or Quanta

Mac OS X:   use the text editor Smultron

Windoze:   use the text editor Aedix (free), or Notepad (but beware of the file extension .txt which is unwanted, the script file must have the extension .scm and not .scm.txt)

Other text editors are ok too, but word processors are not. Do not use Word, OpenOffice or similar tools.

Installation:

Copy correct-horizon.scm into one of the directories registered in the Gimp preferences under Folders/Scripts.

Linux Ubuntu and many others:
  /home/[username]/.gimp-2.n/scripts   or   /usr/share/gimp/2.0/scripts

Linux SuSE:
  /home/[username]/.gimp-2.n/scripts   or   /opt/gnome/share/gimp/2.0/scripts

Windoze:
  C:\.gimp-2.n\scripts   or   C:\program-files\gimp2.n\share\gimp\scripts

Then go to the menu Xtns (in The Gimp) and select Xtns / Script-Fu / Refresh Scripts. That's it.
The script can be called in the menu Layer / Transform / Correct Horizon...

Script-fu correct-horizon.scm for The Gimp (english version)

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;
; SCRIPT-FU-CORRECT-HORIZON corrects a slanted horizon line or a slanted vertical axis
; Copyright (c) 2006-2007 Tharsice Demand <www.td-e.com>
; version 1.00  2006.07.06
; version 1.10  2007.10.24, migration to Gimp 2.4
; version 1.11  2007.11.24  rotation angle determined by rect. selection, problem corrected
; version 1.12  2008.08.08  rotation angle determined by manual input, problem corrected
; version 1.13  2011.07.02  manual input and backward rotation were broken due to changes in Gimp, problem corrected
;
;This program is free software; you can redistribute it and/or
;modify it under the terms of the GNU General Public License
;as published by the Free Software Foundation; either version 2
;of the License, or (at your option) any later version.
;
;This program is distributed in the hope that it will be useful,
;but WITHOUT ANY WARRANTY; without even the implied warranty of
;MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;GNU General Public License for more details.
;
;You should have received a copy of the GNU General Public License
;along with this program; if not, write to the Free Software
;Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
;
;Copy of the license at http://td-e.com/site/gpl.php

(define *correct-horizon-direction-def*
  '(("Forward (clockwise)" GIMP-TRANSFORM-FORWARD)
    ("Backward (counter-clockwise)"  GIMP-TRANSFORM-BACKWARD)))

(define *correct-horizon-interpolation-def*
  '(
    ("None"    GIMP-INTERPOLATION-NONE)
    ("Linear"  GIMP-INTERPOLATION-LINEAR)
    ("Cubic"   GIMP-INTERPOLATION-CUBIC)
    ("Lanczos" GIMP-INTERPOLATION-LANCZOS)
   ))

(define (script-fu-correct-horizon image drawable direction interpolation angleinput crop)

(gimp-image-undo-group-start image)

; init variables
  (let* 
    (
     (image-wi     (car (gimp-image-width image)))
     (image-he     (car (gimp-image-height image)))
     (image-r      (/ image-wi image-he))
     (centerx      (/ image-wi 2))
     (centery      (/ image-he 2))
     (lolimit-wi   (/ image-wi 2))

(bounds       (gimp-selection-bounds image))
     (selexist     (car bounds))
     (selx1        (if selexist (nth 1 bounds) 0))
     (sely1        (if selexist (nth 2 bounds) 0))
     (selx2        (if selexist (nth 3 bounds) image-wi))
     (sely2        (if selexist (nth 4 bounds) image-he))
     (selwi        (- selx2 selx1))
     (selhe        (- sely2 sely1))
     (angleselrad  (atan (/ selhe selwi)))
     (fullselwi    (= selwi image-wi))
     (fullselhe    (= selhe image-he))
     (fullsel      (and fullselwi fullselhe))
     (notfullsel   (not fullsel))

(ii           0)
     (rect-x0      0)
     (rect-y0      0)
     (rect-x1      image-wi)
     (rect-y1      image-he)
     (rect-wi      image-wi)
     (rect-he      image-he)
     (corner00     0)
     (corner01     0)
     (corner10     0)
     (corner11     0)
     (cornersvalid 0)
     (posfound     0)
     (pi           3.1415926535897932384626)
     (angleinrad   (* (/ angleinput 180) pi))
     (angleraw     (if notfullsel angleselrad angleinrad))
     (angleradians (if (< angleraw (/ pi 4)) angleraw (- (/ pi 2) angleraw)))
     ;(angleradians (if (= direction 1) (- angleradians) angleradians))
     (fullselwistr (if fullselwi "true" "false"))
     (fullselhestr (if fullselhe "true" "false"))
     (fullselstr   (if fullsel "true" "false"))
     (notfullselstr (if notfullsel "true" "false"))
    )

; deselect the selection boxes used to define the angle
    (gimp-selection-none image)

; performing the rotation
    (gimp-drawable-transform-rotate drawable angleradians TRUE centerx centery direction interpolation 0 3 1)

; alpha to selection will select the transparent slanted parts obtained after rotation
    (gimp-selection-layer-alpha drawable)

; defining the rectangle inscribed in the slanted rectangle obtained after rotation
    ; searching the inscribed rectangle through a while loop
    (while (< posfound 1)
      ; decrementing the size of the testing rectangle
      (set! rect-wi      (- rect-wi 2))
      (set! rect-he      (/ rect-wi image-r))
      (set! rect-x0      (/ (- image-wi rect-wi) 2))
      (set! rect-y0      (/ (- image-he rect-he) 2))
      (set! rect-x1      (+ rect-x0 rect-wi))
      (set! rect-y1      (+ rect-y0 rect-he))

; getting the selection values of the 4 corners of the testing rectangle, selected=transparent, or not
      (set! corner00 (car (gimp-selection-value image rect-x0 rect-y0)))
      (set! corner01 (car (gimp-selection-value image rect-x0 rect-y1)))
      (set! corner10 (car (gimp-selection-value image rect-x1 rect-y0)))
      (set! corner11 (car (gimp-selection-value image rect-x1 rect-y1)))

; if all 4 corners are valid=not transparent, the rectangle is inscribed in the slanted rectangle
      (if (> corner00 0) 
        (if (> corner01 0) 
          (if (> corner10 0) 
            (if (> corner11 0) 
              (set! cornersvalid 1)
            )
          )
        )
      )

; preparing the exit of the loop
      (if (= cornersvalid 1) (set! posfound 1))
      (if (< rect-wi lolimit-wi) (set! posfound 1))
      (set! ii (+ ii 1))
      (if (> ii 3000) (set! posfound 1))
    ) ; end of loop

; preparing error messages
    (if (< rect-wi lolimit-wi) (define msg1 "Cropping area could not be defined, width/2 reached\n")
                               (define msg1 ""))
    (if (> ii 3000) (define msg2 "Cropping area could not be defined after 3000 loops\n")
                    (define msg2 ""))
    (define msge (string-append msg1 msg2))

; preparing debug messages
    (define msga (string-append "Searched for " (number->string ii) " loops"
      "\n direction=" (number->string direction)
      "\n selexist=" (number->string selexist)
      ;"\n selx1=" (number->string selx1)
      ;"\n sely1=" (number->string sely1)
      ;"\n selx2=" (number->string selx2)
      ;"\n sely2=" (number->string sely2)
      "\n image-wi=" (number->string image-wi)
      "\n image-he=" (number->string image-he)
      "\n selwi=" (number->string selwi)
      "\n selhe=" (number->string selhe)
      ;"\n fullselwi=" fullselwistr
      ;"\n fullselhe=" fullselhestr
      "\n fullsel=" fullselstr
      "\n notfullsel=" notfullselstr
      "\n angleselrad[deg]=" (number->string (* (/ angleselrad pi) 180))
      "\n angleselrad=" (number->string angleselrad)
      "\n angleinput=" (number->string angleinput)
      "\n angleinrad=" (number->string angleinrad)
      "\n angleradians=" (number->string angleradians)
      "\n cornersvalid=" (number->string cornersvalid)
      "\n posfound=" (number->string posfound)
      "\n\nCrop at:"
      "\n x0=" (number->string rect-x0)
      "\n y0=" (number->string rect-y0)
      "\n x1=" (number->string rect-x1)
      "\n y1=" (number->string rect-y1)
      "\n corner00=" (number->string corner00)
      "\n corner10=" (number->string corner10)
      "\n corner01=" (number->string corner01)
      "\n corner11=" (number->string corner11)
     ))

; deciding whether to show error messages
    (if (> (string-length msge) 0)
      (begin
        (define msgz (string-append msge "\n" msga))
        (gimp-message msgz))
      ; else branch for debugging, to be commented in working version
      ;(begin
      ;  (define msgz (string-append msge "\n\n" msga))
      ;  (gimp-message msgz))
    )

(if (eq? crop TRUE)
        (begin
          (gimp-crop image rect-wi rect-he rect-x0 rect-y0)
          (gimp-selection-clear image))
        (gimp-rect-select image rect-x0 rect-y0 rect-wi rect-he 2 0 0))
    (gimp-displays-flush)
  )
  (gimp-image-undo-group-end image)
)

(script-fu-register "script-fu-correct-horizon"
                    "<Image>/Layer/Transform/Correct Horizon..."
                    "Rotates a photo and eliminates the slanted edges after the small rotation. The angle of the rotation is calculated by the script. Before calling the script, draw a rectangular selection where the diagonal is the horizon line or any axis that should be horizontal. Using the rectangular selection tool, click on the horizon line near the left end of the picture, drag towards the right end of the picture and release the mouse button when being exactly on the horizon.\n\nFor more precision, display your picture at 100% or even more if it is rather small. Can be used to correct vertical axes like high buildings too. If the diagonal of a rectangular selection is used to determine the angle, typing an angle has no effect. Crops to a rectangle inscribed in the slanted rectangle obtained after the rotation if the crop check-box is cheked, otherwise only selects the area it would crop to. Keeps the original aspect ratio."
                    "Tharsice Demand <td-e.com>"
                    "Tharsice Demand"
                    "2011.07.10"
                    "RGB RGBA GRAY GRAYA"
                    SF-IMAGE    "Image" 0
                    SF-DRAWABLE "Drawable" 0
                    SF-OPTION   "Rotation Direction" (mapcar car *correct-horizon-direction-def*)
                    SF-OPTION   "Interpolation" (mapcar car *correct-horizon-interpolation-def*)
                    SF-VALUE    "Angle, type it in only if no\n rectangular selection is set" "1.00"
                    SF-TOGGLE   "Crop Image\nunchecked means show selected area to crop and leave" TRUE
)

Sponsorship

If you find the script 'Correct horizon' useful and want to support the developer, you can

License

The GNU general public license applies to the script-fu correct-horizon.scm above and to the various language versions of the script.

Comments
Add a comment to this page

.... ....
... ...
.. ..
. .