matlab代码实现读写PPM和PGM图像

下面是MATLAB代码实现读写PPM和PGM图像的示例：

读取PPM图像：

function [img, map] = readppm(filename)
% READPPM reads a PPM image file
%   [IMG, MAP] = READPPM(FILENAME) reads the PPM image file specified by
%   FILENAME and returns the image data in IMG and the colormap in MAP.
%   If the file is not a PPM image file, an error is thrown.

% Open the file
fid = fopen(filename, 'r');
if (fid < 0)
    error('Unable to open file');
end

% Read the header
header = fgetl(fid);
if (~strcmp(header, 'P6'))
    fclose(fid);
    error('Invalid PPM file');
end
dims = fscanf(fid, '%d %d\n', 2);
maxval = fscanf(fid, '%d\n', 1);

% Read the image data
img = uint8(zeros(dims(2), dims(1), 3));
data = fread(fid, [3 dims(1)*dims(2)], 'uint8');
img(:,:,1) = reshape(data(1,:), dims(1), dims(2))';
img(:,:,2) = reshape(data(2,:), dims(1), dims(2))';
img(:,:,3) = reshape(data(3,:), dims(1), dims(2))';

% Close the file
fclose(fid);

% Create the colormap
map = [];

end

读取PGM图像：

function [img, map] = readpgm(filename)
% READPGM reads a PGM image file
%   [IMG, MAP] = READPGM(FILENAME) reads the PGM image file specified by
%   FILENAME and returns the image data in IMG and the colormap in MAP.
%   If the file is not a PGM image file, an error is thrown.

% Open the file
fid = fopen(filename, 'r');
if (fid < 0)
    error('Unable to open file');
end

% Read the header
header = fgetl(fid);
if (~strcmp(header, 'P5'))
    fclose(fid);
    error('Invalid PGM file');
end
dims = fscanf(fid, '%d %d\n', 2);
maxval = fscanf(fid, '%d\n', 1);

% Read the image data
img = uint8(zeros(dims(2), dims(1)));
data = fread(fid, [1 dims(1)*dims(2)], 'uint8');
img(:,:) = reshape(data, dims(1), dims(2))';

% Close the file
fclose(fid);

% Create the colormap
map = [];

end

写PPM图像：

function writeppm(filename, img)
% WRITEPPM writes a PPM image file
%   WRITEPPM(FILENAME, IMG) writes the image data in IMG to the PPM image
%   file specified by FILENAME.

% Open the file
fid = fopen(filename, 'w');
if (fid < 0)
    error('Unable to open file');
end

% Write the header
fprintf(fid, 'P6\n');
fprintf(fid, '%d %d\n', size(img,2), size(img,1));
fprintf(fid, '255\n');

% Write the image data
fwrite(fid, permute(img, [3,1,2]), 'uint8');

% Close the file
fclose(fid);

end

写PGM图像：

function writepgm(filename, img)
% WRITEPGM writes a PGM image file
%   WRITEPGM(FILENAME, IMG) writes the image data in IMG to the PGM image
%   file specified by FILENAME.

% Open the file
fid = fopen(filename, 'w');
if (fid < 0)
    error('Unable to open file');
end

% Write the header
fprintf(fid, 'P5\n');
fprintf(fid, '%d %d\n', size(img,2), size(img,1));
fprintf(fid, '255\n');

% Write the image data
fwrite(fid, img', 'uint8');

% Close the file
fclose(fid);

end

注意：以上代码中的PPM和PGM格式均为二进制格式。如果需要读取和写入ASCII格式的PPM和PGM图像，请相应地更改代码。