Bitmap/Read a PPM file
Using the data storage type defined on this page for raster images, read an image from a PPM file (binary P6 prefered). (Read the definition of PPM file on Wikipedia.)
You are encouraged to solve this task according to the task description, using any language you may know.
Task: Use write ppm file solution and grayscale image solution with this one in order to convert a color image to grayscale one.
Ada
<lang ada> with Ada.Characters.Latin_1; use Ada.Characters.Latin_1; with Ada.Integer_Text_IO; use Ada.Integer_Text_IO; with Ada.Streams.Stream_IO; use Ada.Streams.Stream_IO;
function Get_PPM (File : File_Type) return Image is
use Ada.Characters.Latin_1; use Ada.Integer_Text_IO;
function Get_Line return String is -- Skips comments
Byte : Character;
Buffer : String (1..80);
begin
loop
for I in Buffer'Range loop
Character'Read (Stream (File), Byte);
if Byte = LF then
exit when Buffer (1) = '#';
return Buffer (1..I - 1);
end if;
Buffer (I) := Byte;
end loop;
if Buffer (1) /= '#' then
raise Data_Error;
end if;
end loop;
end Get_Line;
Height : Integer; Width : Integer;
begin
if Get_Line /= "P6" then
raise Data_Error;
end if;
declare
Line : String := Get_Line;
Start : Integer := Line'First;
Last : Positive;
begin
Get (Line, Width, Last); Start := Start + Last;
Get (Line (Start..Line'Last), Height, Last); Start := Start + Last;
if Start <= Line'Last then
raise Data_Error;
end if;
if Width < 1 or else Height < 1 then
raise Data_Error;
end if;
end;
if Get_Line /= "255" then
raise Data_Error;
end if;
declare
Result : Image (1..Height, 1..Width);
Buffer : String (1..Width * 3);
Index : Positive;
begin
for I in Result'Range (1) loop
String'Read (Stream (File), Buffer);
Index := Buffer'First;
for J in Result'Range (2) loop
Result (I, J) :=
( R => Luminance (Character'Pos (Buffer (Index))),
G => Luminance (Character'Pos (Buffer (Index + 1))),
B => Luminance (Character'Pos (Buffer (Index + 2)))
);
Index := Index + 3;
end loop;
end loop;
return Result;
end;
end Get_PPM; </lang> The implementation propagates Data_Error when the file format is incorrect. End_Error is propagated when the file end is prematurely met. The following example illustrates conversion of a color file to grayscale. <lang ada> declare
F1, F2 : File_Type;
begin
Open (F1, In_File, "city.ppm"); Create (F2, Out_File, "city_grayscale.ppm"); Put_PPM (F2, Color (Grayscale (Get_PPM (F1)))); Close (F1); Close (F2);
end; </lang>
AutoHotkey
<lang AutoHotkey> ppm = ( P6
- lasdjkf
87 09 255 color data... ) MsgBox % ppm_width(ppm) MsgBox % ppm_height(ppm) MsgBox % ppm_colors(ppm) MsgBox % ppm_data(ppm)
ppm_read(file) {
FileRead, ppm, % file Return ppm
}
ppm_width(ppm) {
RegExMatch(ppm, "\R(\d+)\s(\d+)", dim) Return dim1
}
ppm_height(ppm) {
RegExMatch(ppm, "\R(\d+)\s(\d+)", dim) Return dim2
}
ppm_colors(ppm) {
RegExMatch(ppm, "\R(\d+)\D*\R", colors) ; \R stands for any Return colors1
}
ppm_data(ppm) {
pos := RegExMatch(ppm, "\R(\d+)\D*\R", colors) ; \R stands for any newline StringTrimLeft, data, ppm, pos + StrLen(colors1) Return data
} </lang>
C
It is up to the caller to open the file and pass the handler to the function. So this code can be used in Read image file through a pipe without modification. It only understands the P6 file format.
Interface:
<lang c>image get_ppm(FILE *pf);</lang>
Implementation:
<lang c>#include "imglib.h"
- define PPMREADBUFLEN 256
image get_ppm(FILE *pf) {
char buf[PPMREADBUFLEN], *t;
image img;
unsigned int w, h, d;
int r;
if (pf == NULL) return NULL;
t = fgets(buf, PPMREADBUFLEN, pf);
if ( (t == NULL) || ( strncmp(buf, "P6\n", 3) != 0 ) ) return NULL;
do
{ /* Px formats can have # comments after first line */
t = fgets(buf, PPMREADBUFLEN, pf);
if ( t == NULL ) return NULL;
} while ( strncmp(buf, "#", 1) == 0 );
r = sscanf(buf, "%u %u", &w, &h);
if ( r < 2 ) return NULL;
// The program fails if the first byte of the image is equal to 32. because
// the fscanf eats the space and the image is read with some bit less
r = fscanf(pf, "%u\n", &d);
if ( (r < 1) || ( d != 255 ) ) return NULL;
img = alloc_img(w, h);
if ( img != NULL )
{
size_t rd = fread(img->buf, sizeof(pixel), w*h, pf);
if ( rd < w*h )
{
free_img(img);
return NULL;
}
return img;
}
}</lang>
The following acts as a filter to convert a PPM file read from standard input into a PPM gray image, and it outputs the converted image to standard output (see Grayscale image, Write ppm file, and Raster graphics operations in general):
<lang c>#include <stdio.h>
- include "imglib.h"
int main() {
image source; grayimage idest; source = get_ppm(stdin); idest = tograyscale(source); free_img(source); source = tocolor(idest); output_ppm(stdout, source); free_img(source); free_img((image)idest); return 0;
}</lang>
C#
Tested with this solution.
<lang csharp> using System.IO; class PPMReader {
public static Bitmap ReadBitmapFromPPM(string file)
{
var reader = new BinaryReader(new FileStream(file, FileMode.Open));
if (reader.ReadChar() != 'P' || reader.ReadChar() != '6')
return null;
reader.ReadChar(); //Eat newline
string widths = "", heights = "";
char temp;
while ((temp = reader.ReadChar()) != ' ')
widths += temp;
while ((temp = reader.ReadChar()) >= '0' && temp <= '9')
heights += temp;
if (reader.ReadChar() != '2' || reader.ReadChar() != '5' || reader.ReadChar() != '5')
return null;
reader.ReadChar(); //Eat the last newline
int width = int.Parse(widths),
height = int.Parse(heights);
Bitmap bitmap = new Bitmap(width, height);
//Read in the pixels
for (int y = 0; y < height; y++)
for (int x = 0; x < width; x++)
bitmap.SetPixel(x, y, new Bitmap.Color()
{
Red = reader.ReadByte(),
Green = reader.ReadByte(),
Blue = reader.ReadByte()
});
return bitmap;
}
} </lang>
D
This example uses storage defined on Basic bitmap storage problem page.
This is wrap-around defined storage, P6 binary mode.
<lang D> import tango.core.Exception; import tango.io.FileConduit; import tango.io.MappedBuffer; import tango.io.stream.LineStream; import tango.io.protocol.Reader; import tango.text.convert.Integer;
class P6Image {
class BadInputException : Exception { this() { super("Bad file format"); } }
class NoImageException : Exception { this() { super("No image data"); } }
static const char[] type = "P6";
MappedBuffer fileBuf;
ubyte _maxVal, gotImg;
public:
RgbBitmap bitmap;
this (FileConduit input) {
fileBuf = new MappedBuffer(input);
if (processHeader(new LineInput(fileBuf)))
throw new BadInputException;
if (processData(fileBuf))
throw new BadInputException;
}
ubyte maxVal() { return _maxVal; }
int processHeader(LineInput li) {
char[] line;
uint eaten;
li.readln(line);
if (line != type) return 1;
li.readln(line);
// skip comment lines
while (line.length && line[0] == '#') li.readln(line);
auto width = parse(line, 0, &eaten);
auto height = parse(line[eaten..$], 0, &eaten);
if (!eaten || width > 0xffff_ffff || height > 0xffff_ffff) return 1;
li.readln(line);
auto temp = parse(line, 0, &eaten);
if (!eaten || temp > 255) return 1;
_maxVal = temp;
bitmap = RgbBitmap(width, height);
gotImg = 1;
return 0;
}
int processData(MappedBuffer mb) {
if (! gotImg) throw new NoImageException;
mb.fill(bitmap.data);
return 0;
}
} </lang>
Reading from file: <lang D> auto p6 = new P6Image(new FileConduit("image.ppm")); </lang>
E
<lang e>def chr := <import:java.lang.makeCharacter>.asChar
def readPPM(inputStream) {
# Proper native-to-E stream IO facilities have not been designed and
# implemented yet, so we are borrowing Java's. Poorly. This *will* be
# improved eventually.
# Reads one header token, skipping comments and whitespace, and exactly
# one trailing whitespace character
def readToken() {
var token := ""
var c := chr(inputStream.read())
while (c == ' ' || c == '\t' || c == '\r' || c == '\n' || c == '#') {
if (c == '#') {
while (c != '\n') { c := chr(inputStream.read()) }
}
# skip over initial whitespace
c := chr(inputStream.read())
}
while (!(c == ' ' || c == '\t' || c == '\r' || c == '\n')) {
if (c == '#') {
while (c != '\n') { c := chr(inputStream.read()) }
} else {
token += E.toString(c)
c := chr(inputStream.read())
}
}
return token
}
# Header require(readToken() == "P6") def width := __makeInt(readToken()) def height := __makeInt(readToken()) def maxval := __makeInt(readToken())
def size := width * height * 3
# Body # See Basic bitmap storage for the definition and origin of sign() def data := <elib:tables.makeFlexList>.fromType(<type:java.lang.Byte>, size) if (maxval >= 256) { for _ in 1..size { data.push(sign((inputStream.read() * 256 + inputStream.read()) * 255 // maxval)) } } else { for _ in 1..size { data.push(sign(inputStream.read() * 255 // maxval)) } }
def image := makeImage(width, height) image.replace(data.snapshot()) return image
}</lang>Note: As of this writing the grayscale image task has not been implemented, so the task code (below) won't actually run yet. But readPPM above has been tested separately.
<lang e>def readPPMTask(inputFile, outputFile) {
makeGrayscale \ .fromColor(readPPM(<import:java.io.makeFileInputStream>(inputFile))) \ .toColor() \ .writePPM(<import:java.io.makeFileOutputStream>(outputFile))
}</lang>
Forth
: read-ppm { fid -- bmp }
pad dup 80 fid read-line throw 0= abort" Partial line"
s" P6" compare abort" Only P6 supported."
pad dup 80 fid read-line throw 0= abort" Partial line"
0. 2swap >number
1 /string \ skip space
0. 2swap >number
2drop drop nip ( w h )
bitmap { bmp }
pad dup 80 fid read-line throw 0= abort" Partial line"
s" 255" compare abort" Only 8-bits per color channel supported"
0 pad !
bmp bdim
0 do
dup 0 do
pad 3 fid read-file throw
3 - abort" Not enough pixel data in file"
pad @ i j bmp b!
loop
loop drop
bmp ;
\ testing round-trip 4 3 bitmap value test red test bfill green 1 2 test b! s" red.ppm" w/o create-file throw test over write-ppm close-file throw s" red.ppm" r/o open-file throw dup read-ppm value test2 close-file throw : bsize ( bmp -- len ) bdim * pixels bdata ; test dup bsize test2 dup bsize compare . \ 0 if identical
Fortran
(This function is part of module RCImageIO, see Write ppm file)
<lang fortran> subroutine read_ppm(u, img)
integer, intent(in) :: u type(rgbimage), intent(out) :: img integer :: i, j, ncol, cc character(2) :: sign character :: ccode img%width = 0 img%height = 0 nullify(img%red) nullify(img%green) nullify(img%blue)
read(u, '(A2)') sign read(u, *) img%width, img%height read(u, *) ncol
write(0,*) sign write(0,*) img%width, img%height write(0,*) ncol
if ( ncol /= 255 ) return
call alloc_img(img, img%width, img%height)
if ( valid_image(img) ) then
do j=1, img%height
do i=1, img%width
read(u, '(A1)', advance='no', iostat=status) ccode
cc = iachar(ccode)
img%red(i,j) = cc
read(u, '(A1)', advance='no', iostat=status) ccode
cc = iachar(ccode)
img%green(i,j) = cc
read(u, '(A1)', advance='no', iostat=status) ccode
cc = iachar(ccode)
img%blue(i,j) = cc
end do
end do
end if
end subroutine read_ppm</lang>
Notes:
- doing formatted I/O with Fortran is a pain... And unformatted does not mean free; Fortran2003 has streams, but they are not implemented (yet) in GNU Fortran compiler. Here (as in the write part) I've tried to handle the PPM format through formatted I/O. The tests worked but I have not tried still everything.
- comments after the first line are not handled
Haskell
The definition of Bitmap.Netpbm.readNetpbm is given here. <lang haskell>import Bitmap import Bitmap.RGB import Bitmap.Gray import Bitmap.Netpbm
import Control.Monad import Control.Monad.ST
main =
(readNetpbm "original.ppm" :: IO (Image RealWorld RGB)) >>= stToIO . toGrayImage >>= writeNetpbm "new.pgm"</lang>
The above writes a PGM, not a PPM, since the image being output is in grayscale. If you actually want a gray PPM, convert the Image RealWorld Gray back to an Image RealWorld RGB first: <lang haskell>main =
(readNetpbm "original.ppm" :: IO (Image RealWorld RGB)) >>= stToIO . (toRGBImage <=< toGrayImage) >>= writeNetpbm "new.ppm"</lang>
J
Solution: Uses makeRGB from Basic bitmap storage. <lang j> require 'files'
readppm=: monad define
dat=. fread y NB. read from file
't wbyh maxval dat'=. 4{. <;._2 (, LF -. {:) dat NB. parse
'wbyh maxval'=. _99&". &.> wbyh;maxval NB. convert to numeric
if. (_99 e. wbyh,maxval) +. t -.@-: 'P6' do. _1 return. end.
(a. i. dat) makeRGB |.wbyh NB. convert to basic bitmap format
) </lang>
Example:
Using utilities and file from Grayscale image and Write ppm file.
Writes a gray PPM file (a color format) which is bigger than necessary. A PGM file would be more appropriate.
<lang j>
myimg=: readppm jpath '~temp/myimg.ppm' myimgGray=: toColor toGray myimg myimgGray writeppm jpath '~temp/myimgGray.ppm'
</lang>
OCaml
<lang ocaml>let read_ppm ~filename =
let ic = open_in filename in
let line = input_line ic in
if line <> "P6" then invalid_arg "not a P6 ppm file";
let line = input_line ic in
let line =
try if line.[0] = '#' (* skip comments *)
then input_line ic
else line
with _ -> line
in
let width, height =
Scanf.sscanf line "%d %d" (fun w h -> (w, h))
in
let line = input_line ic in
if line <> "255" then invalid_arg "not a 8 bit depth image";
let all_channels =
let kind = Bigarray.int8_unsigned
and layout = Bigarray.c_layout
in
Bigarray.Array3.create kind layout 3 width height
in
let r_channel = Bigarray.Array3.slice_left_2 all_channels 0
and g_channel = Bigarray.Array3.slice_left_2 all_channels 1
and b_channel = Bigarray.Array3.slice_left_2 all_channels 2
in
for y = 0 to pred height do
for x = 0 to pred width do
r_channel.{x,y} <- (input_byte ic);
g_channel.{x,y} <- (input_byte ic);
b_channel.{x,y} <- (input_byte ic);
done;
done;
close_in ic;
(all_channels,
r_channel,
g_channel,
b_channel)</lang>
and converting a given color file to grayscale: <lang ocaml>let () =
let img = read_ppm ~filename:"logo.ppm" in let img = to_color(to_grayscale ~img) in output_ppm ~oc:stdout ~img;
- </lang>
sending the result to stdout allows to see the result without creating a temporary file sending it through a pipe to the display utility of ImageMagick:
ocaml script.ml | display -
Perl
<lang perl>#! /usr/bin/perl
use strict; use Image::Imlib2;
my $img = Image::Imlib2->load("out0.ppm");
- let's do something with it now
$img->set_color(255, 255, 255, 255); $img->draw_line(0,0, $img->width,$img->height); $img->image_set_format("png"); $img->save("out1.png");
exit 0;</lang>
Ruby
Extending Basic_bitmap_storage#Ruby <lang ruby>class Bitmap
# 'open' is a class method
def self.open(filename)
bitmap = nil
File.open(filename, 'r') do |f|
header = [f.gets.chomp, f.gets.chomp, f.gets.chomp]
width, height = header[1].split.map {|n| n.to_i }
if header[0] != 'P6' or header[2] != '255' or width < 1 or height < 1
raise StandardError, "file '#{filename}' does not start with the expected header"
end
f.binmode
bitmap = self.new(width, height)
height.times do |y|
width.times do |x|
# read 3 bytes
red, green, blue = f.read(3).unpack('C3')
bitmap[x,y] = RGBColour.new(red, green, blue)
end
end
end
bitmap
end
end
- create an image: a green cross on a blue background
colour_bitmap = Bitmap.new(20, 30) colour_bitmap.fill(RGBColour::BLUE) colour_bitmap.height.times {|y| [9,10,11].each {|x| colour_bitmap[x,y]=RGBColour::GREEN}} colour_bitmap.width.times {|x| [14,15,16].each {|y| colour_bitmap[x,y]=RGBColour::GREEN}} colour_bitmap.save('testcross.ppm')
- then, convert to grayscale
Bitmap.open('testcross.ppm').to_grayscale!.save('testgray.ppm')</lang>
Tcl
The actual PPM reader is built into the photo image engine: <lang tcl>package require Tk
proc readPPM {image file} {
$image read $file -format ppm
}</lang>
Thus, to read a PPM, convert it to grayscale, and write it back out again becomes this (which requires Tcl 8.6 for try/finally); the PPM reader and writer are inlined because they are trivial at the script level:
<lang tcl>package require Tk
proc grayscaleFile {filename} {
set buffer [image create photo]
try {
$buffer read $filename -format ppm
set w [image width $buffer]
set h [image height $buffer]
for {set x 0} {$x<$w} {incr x} {
for {set y 0} {$y<$h} {incr y} {
lassign [$buffer get $x $y] r g b
set l [expr {int(0.2126*$r + 0.7152*$g + 0.0722*$b)}]
$buffer put [format "#%02x%02x%02x" $l $l $l] -to $x $y
}
}
$buffer write $filename -format ppm
} finally {
image delete $buffer
}
}</lang>
Vedit macro language
// Load a PPM file
// @10 = filename
// On return:
// #10 points to buffer containing pixel data,
// #11 = width, #12 = height.
:LOAD_PPM:
File_Open(@10)
BOF
Search("|X", ADVANCE) // skip "P6"
#11 = Num_Eval(ADVANCE) // #11 = width
Match("|X", ADVANCE) // skip separator
#12 = Num_Eval(ADVANCE) // #12 = height
Match("|X", ADVANCE)
Search("|X", ADVANCE) // skip maxval (assume 255)
Del_Block(0,CP) // remove the header
Return
Example of usage. In addition to LOAD_PPM routine above, you need routine RGB_TO_GRAYSCALE from Grayscale image and routine SAVE_PPM from Write ppm file.
// Load RGB image
Reg_Set(10, "|(USER_MACRO)\example.ppm")
Call("LOAD_PPM")
// Convert to grayscale
#10 = Buf_Num
Call("RGB_TO_GRAYSCALE")
Buf_Switch(#10) Buf_Quit(OK)
// Convert to RGB
Call("GRAYSCALE_TO_RGB")
// Save the image
Reg_Set(10, "|(USER_MACRO)\example_gray.ppm")
Call("SAVE_PPM")
// Cleanup and exit
Buf_Switch(#20) Buf_Quit(OK)
return