Bitmap/PPM conversion through a pipe

From Rosetta Code
Bitmap/PPM conversion through a pipe
You are encouraged to solve this task according to the task description, using any language you may know.

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).


Works with: POSIX version .1-2001

This one uses the ImageMagick convert tool.

/* interface */
void print_jpg(image img, int qual);
#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);

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

#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);

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


(Go 1 should be close)

Using cjpeg:

package main
// Files required to build supporting package raster are found in:
// * Bitmap
// * Write a PPM file
import (
func main() {
b := raster.NewBitmap(400, 300)
// a little extravagant, this draws a design of dots and lines
for i := 0; i < 2000; i++ {
b.SetPxRgb(rand.Intn(400), rand.Intn(300), 0x804020)
for x := 0; x < 400; x++ {
for y := 240; y < 245; y++ {
b.SetPxRgb(x, y, 0x804020)
for y := 260; y < 265; y++ {
b.SetPxRgb(x, y, 0x804020)
for y := 0; y < 300; y++ {
for x := 80; x < 85; x++ {
b.SetPxRgb(x, y, 0x804020)
for x := 95; x < 100; x++ {
b.SetPxRgb(x, y, 0x804020)
// pipe logic
c := exec.Command("cjpeg", "-outfile", "pipeout.jpg")
pipe, err := c.StdinPipe()
if err != nil {
err = c.Start()
if err != nil {
err = b.WritePpmTo(pipe)
if err != nil {
err = pipe.Close()
if err != nil {


Works with: Julia version 0.6
using Images, FileIO
ppmimg = load("data/bitmapInputTest.ppm")
save("data/bitmapOutputTest.jpg", ppmimg)


Works with: Ubuntu 16.04

In order to provide a complete runnable example, we repeat bits of code from other relevant tasks and add code which pipes .ppm data to ImageMagick's 'convert' tool which then writes the corresponding .jpg file to disk.

// Version 1.2.40
import java.awt.Color
import java.awt.Graphics
import java.awt.image.BufferedImage
class BasicBitmapStorage(width: Int, height: Int) {
val image = BufferedImage(width, height, BufferedImage.TYPE_3BYTE_BGR)
fun fill(c: Color) {
val g =
g.color = c
g.fillRect(0, 0, image.width, image.height)
fun setPixel(x: Int, y: Int, c: Color) = image.setRGB(x, y, c.getRGB())
fun getPixel(x: Int, y: Int) = Color(image.getRGB(x, y))
fun main(args: Array<String>) {
// create BasicBitmapStorage object
val width = 640
val height = 640
val bbs = BasicBitmapStorage(width, height)
for (y in 0 until height) {
for (x in 0 until width) {
val c = Color(x % 256, y % 256, (x * y) % 256)
bbs.setPixel(x, y, c)
// now write the object in PPM format to ImageMagick's STDIN via a pipe
// so it can be converted to a .jpg file and written to disk
val pb = ProcessBuilder("convert", "-", "output_piped.jpg")
val buffer = ByteArray(width * 3) // write one line at a time
val proc = pb.start()
val pStdIn = proc.outputStream
pStdIn.use {
val header = "P6\n$width $height\n255\n".toByteArray()
with (it) {
for (y in 0 until height) {
for (x in 0 until width) {
val c = bbs.getPixel(x, y)
buffer[x * 3] =
buffer[x * 3 + 1] =
buffer[x * 3 + 2] =


The Windows command line does not like quotes in the middle of text, so strings have been turned into character codes.



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;
while true do
let c = input_char ic in
print_char c
with End_of_file -> ()

Perl 6[edit]

#!/usr/bin/env perl6
# Reference:
use v6;
class Pixel { has uint8 ($.R, $.G, $.B) }
class Bitmap {
has UInt ($.width, $.height);
has Pixel @!data;
method fill(Pixel $p) {
@!data = $p.clone xx ($!width*$!height)
method pixel(
$i where ^$!width,
$j where ^$!height
--> Pixel
) is rw { @!data[$i*$!height + $j] }
method data { @!data }
role PPM {
method P6 returns Blob {
"P6\n{self.width} {self.height}\n255\n".encode('ascii')
~ flat map { .R, .G, .B },
my Bitmap $b = => 125, height => 125) but PPM;
for flat ^$b.height X ^$b.width -> $i, $j {
$b.pixel($i, $j) = :R($i*2), :G($j*2), :B(255-$i*2);
my $proc = run '/usr/bin/convert','-','output_piped.jpg', :in;
$ $b.P6;
file output_piped.jpg
output_piped.jpg: JPEG image data, JFIF standard 1.01, aspect ratio, density 1x1, segment length 16, baseline, precision 8, 125x125, frames 3


# Create an empty image of 120 x 90 pixels
(setq *Ppm (make (do 90 (link (need 120)))))
# Fill background with green color
(ppmFill *Ppm 0 255 0)
# Draw a diagonal line
(for I 80 (ppmSetPixel *Ppm I I 0 0 0))
# Write to "img.jpg" through a pipe
(ppmWrite *Ppm '("convert" "-" "img.jpg"))


Adapted from
Requires pillow-5.3.0 with Python 3.7.1 32-bit on Windows.
Sample ppm graphics files from

from PIL import Image
im ="boxes_1.ppm")"boxes_1.jpg")

Does not need to pipe through a conversion utility because the Pillow module does the conversion.


(define (ppm->jpeg bitmap [jpg-file "output"] [quality 75])
(define command (format "convert ppm:- -quality ~a jpg:~a.jpg" quality jpg-file))
(match-define (list in out pid err ctrl) (process command))
(bitmap->ppm bitmap out)
(close-input-port in)
(close-output-port out))
(ppm->jpeg bm)


Extends Write ppm file#Ruby. Uses the ImageMagick convert tool. Additionally, for debugging, allow writing in pixmap P3 (ascii) format.

class Pixmap
PIXMAP_FORMATS = ["P3", "P6"] # implemented output formats
PIXMAP_BINARY_FORMATS = ["P6"] # implemented output formats which are binary
def write_ppm(ios, format="P6")
if not PIXMAP_FORMATS.include?(format)
raise NotImplementedError, "pixmap format #{format} has not been implemented"
ios.puts format, "#{@width} #{@height}", "255"
ios.binmode if PIXMAP_BINARY_FORMATS.include?(format)
@height.times do |y|
@width.times do |x|
case format
when "P3" then ios.print @data[x][y].values.join(" "),"\n"
when "P6" then ios.print @data[x][y].values.pack('C3')
def save(filename, opts={:format=>"P6"}), 'w') do |f|
write_ppm(f, opts[:format])
def print(opts={:format=>"P6"})
write_ppm($stdout, opts[:format])
def save_as_jpeg(filename, quality=75)
pipe = IO.popen("convert ppm:- -quality #{quality} jpg:#{filename}", 'w')
image ='file.ppm')


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

Library: Tk
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
However, it is more normal to do this directly with the
Library: TkImg
which is bundled with many Tcl distributions.
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


Translation of: C

Uses the PPM class from

Using the convert utility by ImageMagick:

p:=System.popen(0'|convert ppm:- jpg:"fractal.jpg"|,"w");
img.write(p); p.close();