--- a/ss.c
+++ b/ss.c
@@ -1,8 +1,11 @@
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
 
+#include <png.h>
+
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 static unsigned long
 lowbit(unsigned long x)
@@ -27,6 +30,69 @@
 	return (unsigned char)((v * 255UL + (max / 2UL)) / max);
 }
 
+static int
+haspngext(const char *path)
+{
+	size_t n;
+
+	n = strlen(path);
+	if (n < 4)
+	    return 0;
+	return !strcmp(path + n - 4, ".png");
+}
+
+static int
+writepng(FILE *f, XImage *img, unsigned int w, unsigned int h)
+{
+	png_structp png;
+	png_infop info;
+	unsigned char *row;
+	int ix;
+	int iy;
+
+	png = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
+	if (png == NULL)
+	    return 0;
+	info = png_create_info_struct(png);
+	if (info == NULL) {
+	    png_destroy_write_struct(&png, NULL);
+	    return 0;
+	}
+	if (setjmp(png_jmpbuf(png))) {
+	    png_destroy_write_struct(&png, &info);
+	    return 0;
+	}
+
+	png_init_io(png, f);
+	png_set_IHDR(png, info, w, h, 8,
+	    PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE,
+	    PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
+	png_write_info(png, info);
+
+	row = malloc((size_t)w * 3U);
+	if (row == NULL) {
+	    png_destroy_write_struct(&png, &info);
+	    return 0;
+	}
+
+	for (iy = 0; iy < (int)h; iy++) {
+	    for (ix = 0; ix < (int)w; ix++) {
+	        unsigned long p;
+
+	        p = XGetPixel(img, ix, iy);
+	        row[ix * 3 + 0] = chan(p, img->red_mask);
+	        row[ix * 3 + 1] = chan(p, img->green_mask);
+	        row[ix * 3 + 2] = chan(p, img->blue_mask);
+	    }
+	    png_write_row(png, row);
+	}
+
+	png_write_end(png, info);
+	free(row);
+	png_destroy_write_struct(&png, &info);
+	return 1;
+}
+
 int
 main(int argc, char **argv)
 {
@@ -45,7 +111,7 @@
 	char tail;
 
 	if (argc != 3) {
-	    fprintf(stderr, "usage: ss WIDTHxHEIGHT+X+Y file.ppm\n");
+	    fprintf(stderr, "usage: ss WIDTHxHEIGHT+X+Y file.(ppm|png)\n");
 	    return 1;
 	}
 	if (sscanf(argv[1], "%ux%u+%d+%d%c", &w, &h, &x, &y, &tail) != 4 || w == 0 || h == 0) {
@@ -81,22 +147,32 @@
 	    return 1;
 	}
 
-	fprintf(f, "P6\n%u %u\n255\n", w, h);
-	for (iy = 0; iy < (int)h; iy++) {
-	    for (ix = 0; ix < (int)w; ix++) {
-	        unsigned long p;
-	        unsigned char rgb[3];
+	if (haspngext(argv[2])) {
+	    if (!writepng(f, img, w, h)) {
+	        fprintf(stderr, "png write failed: %s\n", argv[2]);
+	        fclose(f);
+	        XDestroyImage(img);
+	        XCloseDisplay(dpy);
+	        return 1;
+	    }
+	} else {
+	    fprintf(f, "P6\n%u %u\n255\n", w, h);
+	    for (iy = 0; iy < (int)h; iy++) {
+	        for (ix = 0; ix < (int)w; ix++) {
+	            unsigned long p;
+	            unsigned char rgb[3];
 
-	        p = XGetPixel(img, ix, iy);
-	        rgb[0] = chan(p, img->red_mask);
-	        rgb[1] = chan(p, img->green_mask);
-	        rgb[2] = chan(p, img->blue_mask);
-	        if (fwrite(rgb, 1, 3, f) != 3) {
-	            fprintf(stderr, "write failed: %s\n", argv[2]);
-	            fclose(f);
-	            XDestroyImage(img);
-	            XCloseDisplay(dpy);
-	            return 1;
+	            p = XGetPixel(img, ix, iy);
+	            rgb[0] = chan(p, img->red_mask);
+	            rgb[1] = chan(p, img->green_mask);
+	            rgb[2] = chan(p, img->blue_mask);
+	            if (fwrite(rgb, 1, 3, f) != 3) {
+	                fprintf(stderr, "write failed: %s\n", argv[2]);
+	                fclose(f);
+	                XDestroyImage(img);
+	                XCloseDisplay(dpy);
+	                return 1;
+	            }
 	        }
 	    }
 	}
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 CFLAGS   = -std=c89 -Wall -Wextra -Werror -pedantic
 CPPFLAGS = -I/usr/X11R6/include
 LDFLAGS  = -L/usr/X11R6/lib
-LDLIBS   = -lX11
+LDLIBS   = -lX11 -lpng
 
 all: ss