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Preface Introduction API Topic index API Glossary F.A.Q. Copyright
| AFTERImage example 2: Image scaling | demonstrates image loading and scaling |
libAfterImage/tutorials/ASScale
NAME
ASScaleSYNOPSIS
Simple program based on libAfterImage to scale an image.
DESCRIPTION
We will load image and scale it up to new size, specified as command
line arguments
We then display the result in simple window.
After that we would want to wait , until user closes our window.
In this tutorial we will only explain new steps, not described in
previous tutorial. New steps described in this tutorial are :
ASScale .1. Parsing geometry spec.
ASScale .2. Scaling ASImage .
SEE ALSO
Tutorial 1: ASView - explanation of basic steps needed to use
libAfterImage and some other simple things.
SOURCE
#include "../afterbase.h"
#include "../afterimage.h"
#include "common.h"
void usage()
{
printf( "Usage: asscale [-h]|[image [WIDTH[xHEIGHT]]]\n");
printf( "Where: image - is image filename.\n");
printf( " WIDTH - width to scale image to.( Naturally :)\n");
printf( " HEIGHT- height to scale image to.\n");
}
int main(int argc, char* argv[])
{
char *image_file = "rose512.jpg" ;
int dummy, geom_flags = 0;
unsigned int to_width, to_height ;
ASImage *im ;
int clip_x = 0, clip_y = 0, clip_width = 0, clip_height = 0 ;
int slice_x_start = 0, slice_x_end = 0, slice_y_start = 0, slice_y_end = 0 ;
Bool slice_scale = False ;
/* see ASView .1 : */
set_application_name( argv[0] );
if( argc > 1 )
{
int i = 2;
if( strncmp( argv[1], "-h", 2 ) == 0 )
{
usage();
return 0;
}
image_file = argv[1] ;
if( argc > 2 ) /* see ASScale .1 : */
geom_flags = XParseGeometry( argv[2], &dummy, &dummy,
&to_width, &to_height );
while( ++i < argc )
{
if( strncmp( argv[i], "-sx1", 4 ) == 0 && i+1 < argc )
slice_x_start = atoi(argv[++i]) ;
else if( strncmp( argv[i], "-sx2", 4 ) == 0 && i+1 < argc )
slice_x_end = atoi(argv[++i]) ;
else if( strncmp( argv[i], "-sy1", 4 ) == 0 && i+1 < argc )
slice_y_start = atoi(argv[++i]) ;
else if( strncmp( argv[i], "-sy2", 4 ) == 0 && i+1 < argc )
slice_y_end = atoi(argv[++i]) ;
else if( strncmp( argv[i], "-cx", 4 ) == 0 && i+1 < argc )
clip_x = atoi(argv[++i]) ;
else if( strncmp( argv[i], "-cy", 4 ) == 0 && i+1 < argc )
clip_y = atoi(argv[++i]) ;
else if( strncmp( argv[i], "-cwidth", 7 ) == 0 && i+1 < argc )
clip_width = atoi(argv[++i]) ;
else if( strncmp( argv[i], "-cheight", 8 ) == 0 && i+1 < argc )
clip_height = atoi(argv[++i]) ;
else if( strncmp( argv[i], "-ss", 3 ) == 0 )
slice_scale = True ;
}
}else
{
show_warning( "no image file or scale geometry - defaults used:"
" \"%s\" ",
image_file );
usage();
}
/* see ASView .2 : */
im = file2ASImage( image_file, 0xFFFFFFFF, SCREEN_GAMMA, 0, getenv("IMAGE_PATH"), NULL );
if( im != NULL )
{
ASVisual *asv ;
ASImage *scaled_im ;
/* Making sure tiling geometry is sane : */
if( !get_flags(geom_flags, WidthValue ) )
to_width = im->width*2 ;
if( !get_flags(geom_flags, HeightValue ) )
to_height = im->height*2;
printf( "%s: scaling image \"%s\" to %dx%d by factor of %fx%f\n",
get_application_name(), image_file, to_width, to_height,
(double)to_width/(double)(im->width),
(double)to_height/(double)(im->height) );
#ifndef X_DISPLAY_MISSING
{
Window w ;
int screen , depth ;
dpy = XOpenDisplay(NULL);
_XA_WM_DELETE_WINDOW = XInternAtom( dpy,
"WM_DELETE_WINDOW",
False);
screen = DefaultScreen(dpy);
depth = DefaultDepth( dpy, screen );
/* see ASView .3 : */
asv = create_asvisual( dpy, screen , depth, NULL );
/* see ASView .4 : */
w = create_top_level_window( asv, DefaultRootWindow(dpy),
32, 32,
to_width, to_height, 1, 0, NULL,
" ASScale ", image_file );
if( w != None )
{
Pixmap p ;
XMapRaised (dpy, w);
/* see ASScale .2 : */
if( slice_x_start == 0 && slice_x_end == 0 &&
slice_y_start == 0 && slice_y_end == 0 )
{
scaled_im = scale_asimage2( asv, im,
clip_x, clip_y, clip_width, clip_height,
to_width, to_height,
ASA_XImage, 0,
ASIMAGE_QUALITY_DEFAULT );
}else
{
scaled_im = slice_asimage2( asv, im, slice_x_start, slice_x_end,
slice_y_start, slice_y_end,
to_width, to_height, slice_scale,
ASA_XImage, 0,
ASIMAGE_QUALITY_DEFAULT );
}
destroy_asimage( &im );
/* see ASView .5 : */
p = asimage2pixmap(asv, DefaultRootWindow(dpy), scaled_im,
NULL, True );
/* print_storage(NULL); */
destroy_asimage( &scaled_im );
/* see common.c: set_window_background_and_free() : */
p = set_window_background_and_free( w, p );
}
/* see common.c: wait_closedown() : */
wait_closedown(w);
}
#else
asv = create_asvisual( NULL, 0, 0, NULL );
scaled_im = scale_asimage(asv, im, to_width, to_height,
ASA_ASImage, 0,
ASIMAGE_QUALITY_DEFAULT );
/* writing result into the file */
ASImage2file( scaled_im, NULL, "asscale.jpg", ASIT_Jpeg, NULL );
destroy_asimage( &scaled_im );
destroy_asimage( &im );
#endif
}
return 0 ;
}
libAfterImage/tutorials/ASScale.1 [2.1]
SYNOPSIS
Step 1. Parsing the geometry.
DESCRIPTION
Geometry can be specified in WIDTHxHEIGHT+X+Y format. Accordingly we
use standard X function to parse it: XParseGeometry. Returned flags
tell us what values has been specified. Since we only need size -
we check if it is specified and if not - simply default it to twice
as big as original image. Accordingly we use dummy variable to pass
to XParseGeometry.
EXAMPLE
geom_flags = XParseGeometry( argv[3], &dummy, &dummy,
&to_width, &to_height );
libAfterImage/tutorials/ASScale.2 [2.2]
SYNOPSIS
Step 2. Actual scaling the image.
DESCRIPTION
scale_asimage() scales image both up and down, and is very easy to
use - just pass it new size. In this example we use default quality.
Default is equivalent to GOOD which should be sufficient in
most cases. Compression is set to 0 since we do not intend to store
image for long time. Even better - we don't need to store it at all -
all we need is XImage, so we can transfer it to the server easily.
That is why to_xim argument is set to ASA_XImage. As the result obtained
ASImage will not have any data in its buffers, but it will have
ximage member set to point to valid XImage. Subsequently we enjoy
that convenience, by setting use_cached to True in call to
asimage2pixmap . That ought to save us alot of processing.
Scaling algorithm is rather sophisticated and is implementing 4 point
interpolation. Which basically means that we try to approximate each
missing point as an extension of the trend of 4 neighboring points -
two on each side. Closest neighbor's have more weight then outside
ones. 2D scaling is performed by scaling each scanline first, and
then interpolating missing scanlines.
Scaling down is somewhat skimpier, as it amounts to simple averaging
of the multiple pixels. All calculations are done in integer math on
per channel basis, and with precision 24.8 bits per channel per pixel.
EXAMPLE
scaled_im = scale_asimage( asv, im, to_width, to_height,
ASA_XImage, 0, ASIMAGE_QUALITY_DEFAULT );
destroy_asimage( &im );
NOTES
Scaling image up to very large height is much slower then to same
width due to algorithm specifics. Yet even on inferior hardware it
yields decent speeds.
When we successfully scaled image - we no longer need the original -
getting rid of it so it does not clog memory.
SEE ALSO
scale_asimage().
AfterStep Documentation - October 2005 ( 80% complete )
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