Bitmap/PPM conversion through a pipe

Using the data storage type defined on this page for raster images, delegate writing a JPEG file through a pipe using the output_ppm function defined on this other page.

There are various utilities that can be used for this task, for example: cjpeg (package "jpeg-progs" on Linux), ppmtojpeg (package "netpbm" on Linux), convert (from ImageMagick, multi-platform).

C

Works with: POSIX version .1-2001

This one uses the ImageMagick convert tool.

<lang c>/* interface */ void print_jpg(image img, int qual);</lang>

<lang c>#define MAXCMDBUF 100 void print_jpg(image img, int qual) {

  char buf[MAXCMDBUF];
  unsigned int n;
  FILE *pipe;
  
  snprintf(buf, MAXCMDBUF, "convert ppm:- -quality %d jpg:-", qual);
  pipe = popen(buf, "w");
  if ( pipe != NULL )
  {
          fprintf(pipe, "P6\n%d %d\n255\n", img->width, img->height);
          n = img->width * img->height;
          fwrite(img->buf, sizeof(pixel), n, pipe);
          pclose(pipe);
  }

}</lang>

The code that writes to the pipe is the same of output_ppm of course. A complete example is

<lang c>#include "imglib.h"

int main() {

     image img;
     
     img = alloc_img(100,100);
     fill_img(img, 50, 20, 200);
     draw_line(img, 0, 0, 80, 80, 255, 0, 0);
     print_jpg(img, 75);
     free_img(img);

} </lang>

In order to make it working, you must link it with the raster image functions given by the codes here and here

OCaml

<lang ocaml>let print_jpeg ~img ?(quality=96) () =

 let cmd = Printf.sprintf "cjpeg -quality %d" quality in
 (*
 let cmd = Printf.sprintf "ppmtojpeg -quality %d" quality in
 let cmd = Printf.sprintf "convert ppm:- -quality %d jpg:-" quality in
 *)
 let ic, oc = Unix.open_process cmd in
 output_ppm ~img ~oc;
 try
   while true do
     let c = input_char ic in
     print_char c
   done
 with End_of_file -> ()

</lang>

Tcl

Referring to Write ppm file#Tcl and Basic bitmap storage#Tcl

Library: Tk

<lang tcl>package require Tk

proc output_jpeg {image filename {quality 75}} {

   set f [open |[list convert ppm:- -quality $quality jpg:- > $filename] w]
   fconfigure $f -translation binary
   puts -nonewline $f [$image data -format ppm]
   close $f

}</lang>

However, it is more normal to do this directly with the

Library: TkImg

which is bundled with many Tcl distributions.

<lang tcl>package require Tk package require img::jpeg

proc output_jpeg {image filename} {

   $image write $filename -format jpeg

} set img [image create photo -filename filename.ppm] output_jpeg $img filename.jpg</lang>