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diff --git a/.gitignore b/.gitignore
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+++ b/.gitignore
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+Makefile
+Makefile.in
+aclocal.m4
+*.go
+*.cache
+*.log
+config.status
+configure
+*.tar.gz
+pre-inst-env
+build-aux/install-sh
+build-aux/missing
+*.trs
+*~
diff --git a/COPYING b/COPYING
new file mode 100644
index 0000000..f288702
--- /dev/null
+++ b/COPYING
@@ -0,0 +1,674 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
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+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    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 3 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, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/Makefile.am b/Makefile.am
new file mode 100644
index 0000000..b352407
--- /dev/null
+++ b/Makefile.am
@@ -0,0 +1,57 @@
+## extract-green-color --- Extract green color from a photo of LCD Writing Tablet.
+## Copyright © 2021 Masaya Tojo <masaya@tojo.tokyo>
+##
+## This file is part of extract-green-color.
+##
+## Extract-green-color 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 3 of the License, or (at your option) any later version.
+##
+## Extract-green-color 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 extract-green-color.  If not, see
+## <http://www.gnu.org/licenses/>.
+
+GOBJECTS = $(SOURCES:%.scm=%.go)
+
+nobase_mod_DATA = $(SOURCES) $(NOCOMP_SOURCES)
+nobase_go_DATA = $(GOBJECTS)
+
+# Make sure source files are installed first, so that the mtime of
+# installed compiled files is greater than that of installed source
+# files.  See
+# <http://lists.gnu.org/archive/html/guile-devel/2010-07/msg00125.html>
+# for details.
+guile_install_go_files = install-nobase_goDATA
+$(guile_install_go_files): install-nobase_modDATA
+
+CLEANFILES = $(GOBJECTS)
+GUILE_WARNINGS = -Wunbound-variable -Warity-mismatch -Wformat
+EXTRA_DIST = $(SOURCES) $(NOCOMP_SOURCES)
+SUFFIXES = .scm .go
+.scm.go:
+	$(AM_V_GEN)$(top_builddir)/pre-inst-env $(GUILD) compile $(GUILE_WARNINGS) -o "$@" "$<"
+
+moddir=$(prefix)/share/guile/site/$(GUILE_EFFECTIVE_VERSION)
+godir=$(libdir)/guile/$(GUILE_EFFECTIVE_VERSION)/site-ccache
+
+bin_SCRIPTS =              \
+  extract-green-color.scm
+
+SOURCES =                  \
+  extract-green-color.scm
+
+AM_SCM_LOG_DRIVER_FLAGS = --brief=yes
+
+AM_SCM_LOG_FLAGS = --no-auto-compile -L "$(top_srcdir)"
+
+EXTRA_DIST +=               \
+  README.md                 \
+  bootstrap                 \
+  pre-inst-env.in           \
+  guix.scm
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..dea1206
--- /dev/null
+++ b/README.md
@@ -0,0 +1,3 @@
+# extract-green-color
+
+Extract green color from a photo of LCD Writing Tablet.
diff --git a/bootstrap b/bootstrap
new file mode 100755
index 0000000..872167c
--- /dev/null
+++ b/bootstrap
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+autoreconf -vif
diff --git a/configure.ac b/configure.ac
new file mode 100644
index 0000000..a2969e8
--- /dev/null
+++ b/configure.ac
@@ -0,0 +1,13 @@
+AC_INIT([extract-green-color], [1.0.0])
+AC_CONFIG_SRCDIR([extract-green-color.scm])
+AC_CONFIG_AUX_DIR([build-aux])
+AM_INIT_AUTOMAKE([-Wall -Werror foreign])
+AM_SILENT_RULES([yes])
+
+GUILE_PKG([2.2])
+GUILE_PROGS
+
+AC_CONFIG_FILES([Makefile])
+AC_CONFIG_FILES([pre-inst-env], [chmod +x pre-inst-env])
+
+AC_OUTPUT
diff --git a/extract-green-color.scm b/extract-green-color.scm
new file mode 100755
index 0000000..2d56d6b
--- /dev/null
+++ b/extract-green-color.scm
@@ -0,0 +1,115 @@
+#!/usr/bin/env -S guile -e main -s
+!#
+;;; extract-green-color --- Extract green color from a photo of LCD Writing Tablet.
+;;; Copyright © 2021 Masaya Tojo <masaya@tojo.tokyo>
+;;;
+;;; This file is part of extract-green-color.
+;;;
+;;; Extract-green-color 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 3 of the License, or (at your option) any later version.
+;;;
+;;; Extract-green-color 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 extract-green-color.  If not, see
+;;; <http://www.gnu.org/licenses/>.
+
+(use-modules (cv)
+             ((cv idata) #:prefix idata:)
+             (srfi srfi-8)
+             (ice-9 getopt-long)
+             (ice-9 match))
+
+(define (rgb->hsv r g b)
+  (let* ((max* (max r g b))
+         (min* (min r g b)) (max-min* (- max* min*)))
+    (let ((h (cond
+              ((= max* min*) #f)
+              ((= b min*) (+ (* 60 (/ (- g r) max-min*)) 60))
+              ((= r min*) (+ (* 60 (/ (- b g) max-min*)) 180))
+              (else       (+ (* 60 (/ (- r b) max-min*)) 300))))
+          (s (/ max-min* max*))
+          (v (/ max* 256.0)))
+      (values h s v))))
+
+(define (im-resize* img new-w)
+  (match img
+    ((w h _ _)
+     (im-resize img new-w (floor (* h (/ new-w w)))))))
+
+(define* (extract-green-color img
+                              hue-minus-threshold
+                              hue-plus-threshold
+                              saturation-threshold
+                              value-treshold)
+  (match img
+    ((w h _ _)
+     (let ((out (im-make w h 3 0)))
+       (do ((i 0 (1+ i)))
+           ((= i h))
+         (do ((j 0 (1+ j)))
+             ((= j w))
+           (let ((r (im-fast-ref img i j 0))
+                 (g (im-fast-ref img i j 1))
+                 (b (im-fast-ref img i j 2)))
+             (receive (h s v) (rgb->hsv r g b)
+               (when (and h
+                          (<= (- 120 hue-minus-threshold)
+                              h
+                              (+ 120 hue-plus-threshold))
+                          (>= s saturation-threshold)
+                          (>= s value-treshold))
+                 (idata:im-fast-set! out i j 0 r)
+                 (idata:im-fast-set! out i j 1 g)
+                 (idata:im-fast-set! out i j 2 b))))))
+       out))))
+
+(define (show-usage)
+  (format (current-error-port)
+          "Usage: extract-green-color.scm [OPTION]... input-file output-file
+Extract green color from input-file and save to output-file.
+
+Options:
+  -m, --hue-minus       hue threshold to express distance to red (default 60)
+  -p, --hue-plus        hue threshold to express distance to blue (default 60)
+  -s, --saturation      saturation threshold (default 0)
+  -v, --value           value threshold (default 0)
+
+  -h, --help            show this help
+  -V, --version         show version information
+"))
+
+(define (show-version)
+  (format (current-error-port)
+          "extract-green-color.scm 1.0~%"))
+
+(define (main args)
+  (let* ((option-spec `((version (single-char #\V))
+                        (help (single-char #\h))
+                        (hue-minus (single-char #\m) (value #t) (predicate ,string->number))
+                        (hue-plus (single-char #\p) (value #t) (predicate ,string->number))
+                        (saturation (single-char #\s) (value #t) (predicate ,string->number))
+                        (value (single-char #\v) (value #t) (predicate ,string->number))))
+         (options (getopt-long args option-spec)))
+    (when (option-ref options 'help #f)
+      (show-usage)
+      (exit 1))
+    (when (option-ref options 'version #f)
+      (show-version)
+      (exit 1))
+    (unless (= 2 (length (option-ref options '() '())))
+      (format (current-error-port) "extract-green-color.scm: non-option argument count must be 2~%")
+      (show-usage)
+      (exit 1))
+    (match-let (((input-file output-file) (option-ref options '() '())))
+      (im-save (extract-green-color (im-load input-file)
+                                    (string->number (option-ref options 'hue-minus "60"))
+                                    (string->number (option-ref options 'hue-plus "60"))
+                                    (string->number (option-ref options 'saturation "0.0"))
+                                    (string->number (option-ref options 'value "0.0")))
+               output-file))))
diff --git a/guix.scm b/guix.scm
new file mode 100644
index 0000000..87ed50a
--- /dev/null
+++ b/guix.scm
@@ -0,0 +1,51 @@
+;;; extract-green-color --- Extract green color from a photo of LCD Writing Tablet.
+;;; Copyright © 2021 Masaya Tojo <masaya@tojo.tokyo>
+;;;
+;;; This file is part of extract-green-color.
+;;;
+;;; Extract-green-color 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 3 of the License, or (at your option) any later version.
+;;;
+;;; Extract-green-color 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 extract-green-color.  If not, see
+;;; <http://www.gnu.org/licenses/>.
+
+(use-modules (guix packages)
+             ((guix licenses) #:prefix license:)
+             (guix git-download)
+             (guix build-system gnu)
+             (gnu packages)
+             (gnu packages autotools)
+             (gnu packages guile)
+             (gnu packages guile-xyz)
+             (gnu packages pkg-config)
+             (gnu packages texinfo))
+
+(define extract-green-color
+  (package
+   (name "extract-green-color")
+   (version "1.0.0")
+   (source (string-append (getcwd) "/extract-green-color-" version ".tar.gz"))
+   (build-system gnu-build-system)
+   (native-inputs
+    `(("autoconf" ,autoconf)
+      ("automake" ,automake)
+      ("pkg-config" ,pkg-config)
+      ("texinfo" ,texinfo)))
+   (inputs
+    `(("guile" ,guile-2.2)
+      ("guile-cv" ,guile-cv)))
+   (synopsis "Extract green color from a photo of LCD Writing Tablet")
+   (description "This package provides script to extract green color
+from a photo of LCD Writing Tablet.")
+   (home-page "https://git.tojo.tokyo/extract-green-color.git")
+   (license license:gpl3+)))
+
+extract-green-color
diff --git a/pre-inst-env.in b/pre-inst-env.in
new file mode 100644
index 0000000..f0fc4d5
--- /dev/null
+++ b/pre-inst-env.in
@@ -0,0 +1,32 @@
+#!/bin/sh
+
+## extract-green-color --- Extract green color from a photo of LCD Writing Tablet.
+## Copyright © 2021 Masaya Tojo <masaya@tojo.tokyo>
+##
+## This file is part of extract-green-color.
+##
+## Extract-green-color 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 3 of the License, or (at your option) any later version.
+##
+## Extract-green-color 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 extract-green-color.  If not, see
+## <http://www.gnu.org/licenses/>.
+
+abs_top_srcdir="`cd "@abs_top_srcdir@" > /dev/null; pwd`"
+abs_top_builddir="`cd "@abs_top_builddir@" > /dev/null; pwd`"
+
+GUILE_LOAD_COMPILED_PATH="$abs_top_builddir${GUILE_LOAD_COMPILED_PATH:+:}$GUILE_LOAD_COMPILED_PATH"
+GUILE_LOAD_PATH="$abs_top_builddir:$abs_top_srcdir${GUILE_LOAD_PATH:+:}:$GUILE_LOAD_PATH"
+export GUILE_LOAD_COMPILED_PATH GUILE_LOAD_PATH
+
+PATH="$abs_top_builddir:$PATH"
+export PATH
+
+exec "$@"