NAME¶

asscale - demonstrates image loading and scaling libAfterImage/tutorials/ASScale

NAMEASScale¶

SYNOPSIS¶

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 ;
Display *dpy = NULL;

/* 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);
dpy = NULL;
} #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 a lot 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().