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gimp/plug-ins/common/colortoalpha.c

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/*
* Color To Alpha plug-in v1.0 by Seth Burgess, sjburges@gimp.org 1999/05/14
* with algorithm by clahey
*/
/* The GIMP -- an image manipulation program
* Copyright (C) 1995 Spencer Kimball and Peter Mattis
*
* 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
#include "config.h"
#include <libgimp/gimp.h>
#include <libgimp/gimpui.h>
#include "libgimp/stdplugins-intl.h"
#define PLUG_IN_PROC "plug-in-colortoalpha"
#define PLUG_IN_BINARY "colortoaplha"
#define PRV_WIDTH 40
#define PRV_HEIGHT 20
typedef struct
{
GimpRGB color;
gboolean preview;
} C2AValues;
/* Declare local functions.
*/
static void query (void);
static void run (const gchar *name,
gint nparams,
const GimpParam *param,
gint *nreturn_vals,
GimpParam **return_vals);
static inline void color_to_alpha (GimpRGB *src,
const GimpRGB *color);
static void to_alpha_func (const guchar *src,
guchar *dest,
gint bpp,
gpointer data);
/* UI stuff */
static gboolean color_to_alpha_dialog (GimpDrawable *drawable);
static void color_to_alpha_preview (GimpPreview *preview,
GimpDrawable *drawable);
const GimpPlugInInfo PLUG_IN_INFO =
{
NULL, /* init_proc */
NULL, /* quit_proc */
query, /* query_proc */
run, /* run_proc */
};
static C2AValues pvals =
{
{ 1.0, 1.0, 1.0, 1.0 }, /* white default */
TRUE /* preview */
};
MAIN ()
static void
query (void)
{
static const GimpParamDef args[] =
{
{ GIMP_PDB_INT32, "run-mode", "Interactive, non-interactive" },
{ GIMP_PDB_IMAGE, "image", "Input image (unused)" },
{ GIMP_PDB_DRAWABLE, "drawable", "Input drawable" },
{ GIMP_PDB_COLOR, "color", "Color to remove" }
};
gimp_install_procedure (PLUG_IN_PROC,
N_("Convert a specified color to transparency"),
"This replaces as much of a given color as possible "
"in each pixel with a corresponding amount of alpha, "
"then readjusts the color accordingly.",
"Seth Burgess",
"Seth Burgess <sjburges@gimp.org>",
"7th Aug 1999",
N_("Color to _Alpha..."),
"RGB*",
GIMP_PLUGIN,
G_N_ELEMENTS (args), 0,
args, NULL);
gimp_plugin_menu_register (PLUG_IN_PROC,
"<Image>/Colors/Modify");
gimp_plugin_menu_register (PLUG_IN_PROC,
"<Image>/Layer/Transparency/Modify");
}
static void
run (const gchar *name,
gint nparams,
const GimpParam *param,
gint *nreturn_vals,
GimpParam **return_vals)
{
static GimpParam values[1];
GimpDrawable *drawable;
GimpPDBStatusType status = GIMP_PDB_SUCCESS;
GimpRunMode run_mode;
gint32 image_ID;
run_mode = param[0].data.d_int32;
*nreturn_vals = 1;
*return_vals = values;
INIT_I18N ();
values[0].type = GIMP_PDB_STATUS;
values[0].data.d_status = status;
image_ID = param[1].data.d_image;
drawable = gimp_drawable_get (param[2].data.d_drawable);
switch (run_mode)
{
case GIMP_RUN_INTERACTIVE:
gimp_get_data (PLUG_IN_PROC, &pvals);
if (! color_to_alpha_dialog (drawable))
{
gimp_drawable_detach (drawable);
return;
}
break;
case GIMP_RUN_NONINTERACTIVE:
if (nparams != 4)
status = GIMP_PDB_CALLING_ERROR;
if (status == GIMP_PDB_SUCCESS)
pvals.color = param[3].data.d_color;
break;
case GIMP_RUN_WITH_LAST_VALS:
gimp_get_data (PLUG_IN_PROC, &pvals);
break;
default:
break;
}
if (status == GIMP_PDB_SUCCESS &&
gimp_drawable_is_rgb (drawable->drawable_id) &&
gimp_drawable_is_layer (drawable->drawable_id))
{
gboolean lock_alpha;
gimp_image_undo_group_start (image_ID);
/* Add alpha if not present */
gimp_layer_add_alpha (drawable->drawable_id);
/* Reget the drawable, bpp might have changed */
drawable = gimp_drawable_get (drawable->drawable_id);
/* Unset 'Lock alpha' */
lock_alpha = gimp_layer_get_lock_alpha (drawable->drawable_id);
gimp_layer_set_lock_alpha (drawable->drawable_id, FALSE);
gimp_progress_init (_("Removing color"));
gimp_rgn_iterate2 (drawable, 0 /* unused */, to_alpha_func, NULL);
gimp_layer_set_lock_alpha (drawable->drawable_id, lock_alpha);
gimp_image_undo_group_end (image_ID);
if (run_mode != GIMP_RUN_NONINTERACTIVE)
gimp_displays_flush ();
}
gimp_drawable_detach (drawable);
if (run_mode == GIMP_RUN_INTERACTIVE)
gimp_set_data (PLUG_IN_PROC, &pvals, sizeof (pvals));
values[0].data.d_status = status;
}
static inline void
color_to_alpha (GimpRGB *src,
const GimpRGB *color)
{
GimpRGB alpha;
alpha.a = src->a;
if (color->r < 0.0001)
alpha.r = src->r;
else if (src->r > color->r)
alpha.r = (src->r - color->r) / (1.0 - color->r);
else if (src->r < color->r)
alpha.r = (color->r - src->r) / color->r;
else alpha.r = 0.0;
if (color->g < 0.0001)
alpha.g = src->g;
else if (src->g > color->g)
alpha.g = (src->g - color->g) / (1.0 - color->g);
else if (src->g < color->g)
alpha.g = (color->g - src->g) / (color->g);
else alpha.g = 0.0;
if (color->b < 0.0001)
alpha.b = src->b;
else if (src->b > color->b)
alpha.b = (src->b - color->b) / (1.0 - color->b);
else if (src->b < color->b)
alpha.b = (color->b - src->b) / (color->b);
else alpha.b = 0.0;
if (alpha.r > alpha.g)
{
if (alpha.r > alpha.b)
{
src->a = alpha.r;
}
else
{
src->a = alpha.b;
}
}
else if (alpha.g > alpha.b)
{
src->a = alpha.g;
}
else
{
src->a = alpha.b;
}
if (src->a < 0.0001)
return;
src->r = (src->r - color->r) / src->a + color->r;
src->g = (src->g - color->g) / src->a + color->g;
src->b = (src->b - color->b) / src->a + color->b;
src->a *= alpha.a;
}
/*
* An excerpt from a discussion on #gimp that sheds some light on the ideas
* behind the algorithm that is being used here.
*
<clahey> so if a1 > c1, a2 > c2, and a3 > c2 and a1 - c1 > a2-c2, a3-c3,
then a1 = b1 * alpha + c1 * (1-alpha)
So, maximizing alpha without taking b1 above 1 gives
a1 = alpha + c1(1-alpha) and therefore alpha = (a1-c1) / (1-c1).
<sjburges> clahey: btw, the ordering of that a2, a3 in the white->alpha didn't
matter
<clahey> sjburges: You mean that it could be either a1, a2, a3 or
a1, a3, a2?
<sjburges> yeah
<sjburges> because neither one uses the other
<clahey> sjburges: That's exactly as it should be. They are both just
getting reduced to the same amount, limited by the the darkest
color.
<clahey> Then a2 = b2 * alpha + c2 * (1- alpha). Solving for b2 gives
b2 = (a1-c2)/alpha + c2.
<sjburges> yeah
<clahey> That gives us are formula for if the background is darker than the
foreground? Yep.
<clahey> Next if a1 < c1, a2 < c2, a3 < c3, and c1-a1 > c2-a2, c3-a3, and
by our desired result a1 = b1 * alpha + c1 * (1-alpha),
we maximize alpha without taking b1 negative gives
alpha = 1 - a1 / c1.
<clahey> And then again, b2 = (a2-c2) / alpha + c2 by the same formula.
(Actually, I think we can use that formula for all cases, though
it may possibly introduce rounding error.
<clahey> sjburges: I like the idea of using floats to avoid rounding error.
Good call.
*/
static void
to_alpha_func (const guchar *src,
guchar *dest,
gint bpp,
gpointer data)
{
GimpRGB color;
if (bpp == 3)
gimp_rgba_set_uchar (&color, src[0], src[1], src[2], 255);
else
gimp_rgba_set_uchar (&color, src[0], src[1], src[2], src[3]);
color_to_alpha (&color, &pvals.color);
gimp_rgba_get_uchar (&color, &dest[0], &dest[1], &dest[2], &dest[3]);
}
static void
color_to_alpha_preview (GimpPreview *preview,
GimpDrawable *drawable)
{
GimpPixelRgn src_rgn;
gint x, y;
gint width, height;
gint bpp;
gint i;
guchar *src, *dest;
bpp = drawable->bpp;
gimp_preview_get_position (preview, &x, &y);
gimp_preview_get_size (preview, &width, &height);
dest = g_new (guchar, width * height * 4);
src = g_new (guchar, width * height * bpp);
gimp_pixel_rgn_init (&src_rgn, drawable,
x, y, width, height,
FALSE, FALSE);
gimp_pixel_rgn_get_rect (&src_rgn, src, x, y, width, height);
for (i = 0; i < width * height; i++)
to_alpha_func (src + i * bpp, dest + i * 4, bpp, NULL);
g_free (src);
/* Our code assumes that the drawable has an alpha channel (and adds
* one later if the effect is actually performed). For that reason
* we have to take care when drawing the preview.
*/
if (bpp == 4)
{
gimp_preview_draw_buffer (preview, dest, width * 4);
}
else
{
/* This is not correct because we ignore the selection, but it
* is the best we can easily do.
*/
gimp_preview_area_draw (GIMP_PREVIEW_AREA (preview->area),
0, 0, width, height,
GIMP_RGBA_IMAGE, dest, width * 4);
}
g_free (dest);
}
static gboolean
color_to_alpha_dialog (GimpDrawable *drawable)
{
GtkWidget *dialog;
GtkWidget *main_vbox;
GtkWidget *preview;
GtkWidget *hbox;
GtkWidget *button;
GtkWidget *label;
gboolean run;
gimp_ui_init (PLUG_IN_BINARY, TRUE);
dialog = gimp_dialog_new (_("Color to Alpha"), PLUG_IN_BINARY,
NULL, 0,
gimp_standard_help_func, PLUG_IN_PROC,
GTK_STOCK_CANCEL, GTK_RESPONSE_CANCEL,
GTK_STOCK_OK, GTK_RESPONSE_OK,
NULL);
gtk_dialog_set_alternative_button_order (GTK_DIALOG (dialog),
GTK_RESPONSE_OK,
GTK_RESPONSE_CANCEL,
-1);
gimp_window_set_transient (GTK_WINDOW (dialog));
main_vbox = gtk_vbox_new (FALSE, 12);
gtk_container_set_border_width (GTK_CONTAINER (main_vbox), 12);
gtk_container_add (GTK_CONTAINER (GTK_DIALOG (dialog)->vbox), main_vbox);
gtk_widget_show (main_vbox);
preview = gimp_drawable_preview_new (drawable, &pvals.preview);
gtk_box_pack_start_defaults (GTK_BOX (main_vbox), preview);
gtk_widget_show (preview);
g_signal_connect (preview, "invalidated",
G_CALLBACK (color_to_alpha_preview),
drawable);
hbox = gtk_hbox_new (FALSE, 6);
gtk_box_pack_start (GTK_BOX (main_vbox), hbox, FALSE, FALSE, 0);
gtk_widget_show (hbox);
label = gtk_label_new (_("From:"));
gtk_box_pack_start (GTK_BOX (hbox), label, FALSE, FALSE, 0);
gtk_widget_show (label);
button = gimp_color_button_new (_("Color to Alpha Color Picker"),
PRV_WIDTH, PRV_HEIGHT,
&pvals.color,
GIMP_COLOR_AREA_FLAT);
gimp_color_button_set_update (GIMP_COLOR_BUTTON (button), TRUE);
gtk_box_pack_start (GTK_BOX (hbox), button, TRUE, TRUE, 0);
gtk_widget_show (button);
g_signal_connect (button, "color-changed",
G_CALLBACK (gimp_color_button_get_color),
&pvals.color);
g_signal_connect_swapped (button, "color-changed",
G_CALLBACK (gimp_preview_invalidate),
preview);
label = gtk_label_new (_("to alpha"));
gtk_box_pack_start (GTK_BOX (hbox), label, FALSE, FALSE, 0);
gtk_widget_show (label);
gtk_widget_show (dialog);
run = (gimp_dialog_run (GIMP_DIALOG (dialog)) == GTK_RESPONSE_OK);
gtk_widget_destroy (dialog);
return run;
}
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