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Bitmap/Read a PPM file: Difference between revisions
Added Erlang example
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.writePPM(<import:java.io.makeFileOutputStream>(outputFile))
}</lang>
=={{header|Erlang}}==
<lang erlang>
% This module provides basic operations on ppm files:
% Read from file, create ppm in memory (from generic bitmap) and save to file.
% Writing PPM files was introduced in roseta code task 'Bitmap/Write a PPM file'
% but the same code is included here to provide whole set of operations on ppm
% needed for purposes of this task.
-module(ppm).
-export([ppm/1, write/2, read/1]).
% constants for writing ppm file
-define(WHITESPACE, <<10>>).
-define(SPACE, <<32>>).
% constants for reading ppm file
-define(WHITESPACES, [9, 10, 13, 32]).
-define(PPM_HEADER, "P6").
% data structure introduced in task Bitmap (module ros_bitmap.erl)
-record(bitmap, {
mode = rgb,
pixels = nil,
shape = {0, 0}
}).
%%%%%%%%% API %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% read ppm file from file
read(Filename) ->
{ok, File} = file:read_file(Filename),
parse(File).
% create ppm image from bitmap record
ppm(Bitmap) ->
{Width, Height} = Bitmap#bitmap.shape,
Pixels = ppm_pixels(Bitmap),
Maxval = 255, % original ppm format maximum
list_to_binary([
header(), width_and_height(Width, Height), maxval(Maxval), Pixels]).
% write bitmap as ppm file
write(Bitmap, Filename) ->
Ppm = ppm(Bitmap),
{ok, File} = file:open(Filename, [binary, write]),
file:write(File, Ppm),
file:close(File).
%%%%%%%%% Reading PPM %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
parse(Binary) ->
{?PPM_HEADER, Data} = get_next_token(Binary),
{Width, HeightAndRest} = get_next_token(Data),
{Height, MaxValAndRest} = get_next_token(HeightAndRest),
{_MaxVal, RawPixels} = get_next_token(MaxValAndRest),
Shape = {list_to_integer(Width), list_to_integer(Height)},
Pixels = load_pixels(RawPixels),
#bitmap{pixels=Pixels, shape=Shape}.
% load binary as a list of RGB triplets
load_pixels(Binary) when is_binary(Binary)->
load_pixels([], Binary).
load_pixels(Acc, <<>>) ->
array:from_list(lists:reverse(Acc));
load_pixels(Acc, <<R, G, B, Rest/binary>>) ->
load_pixels([<<R,G,B>>|Acc], Rest).
is_whitespace(Byte) ->
lists:member(Byte, ?WHITESPACES).
% get next part of PPM file, skip whitespaces, and return the rest of a binary
get_next_token(Binary) ->
get_next_token("", true, Binary).
get_next_token(CurrentToken, false, <<Byte, Rest/binary>>) ->
case is_whitespace(Byte) of
true ->
{lists:reverse(CurrentToken), Rest};
false ->
get_next_token([Byte | CurrentToken], false, Rest)
end;
get_next_token(CurrentToken, true, <<Byte, Rest/binary>>) ->
case is_whitespace(Byte) of
true ->
get_next_token(CurrentToken, true, Rest);
false ->
get_next_token([Byte | CurrentToken], false, Rest)
end.
%%%%%%%%% Writing PPM %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
header() ->
[<<"P6">>, ?WHITESPACE].
width_and_height(Width, Height) ->
[encode_decimal(Width), ?SPACE, encode_decimal(Height), ?WHITESPACE].
maxval(Maxval) ->
[encode_decimal(Maxval), ?WHITESPACE].
ppm_pixels(Bitmap) ->
% 24 bit color depth
array:to_list(Bitmap#bitmap.pixels).
encode_decimal(Number) ->
integer_to_list(Number).
</lang>
Usage in accordance with Grayscale Task:
<lang erlang>
Colorful = ppm:read("colorful.ppm"),
Gray = ros_bitmap:convert(ros_bitmap:convert(Colorful, grey), rgb),
ppm:save(Gray, "gray.ppm"),
</lang>
=={{header|Euphoria}}==
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