matlab代码读写PPM和PGM图像

以下是使用MATLAB读取和写入PPM和PGM图像的示例代码：

读取PPM图像：

function img = read_ppm(filename)
    % Open the file for reading
    fid = fopen(filename, 'rb');

    % Read the header
    header = fgets(fid);

    % Check if the file is P6 format
    if ~strcmp(header, 'P6\n')
        error('Not a P6 PPM file');
    end

    % Read the width, height, and max value
    w = fscanf(fid, '%d', 1);
    h = fscanf(fid, '%d', 1);
    maxval = fscanf(fid, '%d', 1);

    % Read the image data
    data = fread(fid, [3, w * h], 'uint8');

    % Close the file
    fclose(fid);

    % Reshape the data and convert to double
    img = double(reshape(data, [3, w, h]));
    img = permute(img, [3, 2, 1]);

    % Normalize to [0,1] range
    img = img / maxval;
end

写入PPM图像：

function write_ppm(filename, img)
    % Open the file for writing
    fid = fopen(filename, 'wb');

    % Write the header
    fprintf(fid, 'P6\n');

    % Write the width, height, and max value
    [h, w, d] = size(img);
    fprintf(fid, '%d %d\n', w, h);
    fprintf(fid, '255\n');

    % Convert to uint8 and write the data
    data = uint8(round(img * 255));
    data = permute(data, [3, 2, 1]);
    fwrite(fid, data, 'uint8');

    % Close the file
    fclose(fid);
end

读取PGM图像：

function img = read_pgm(filename)
    % Open the file for reading
    fid = fopen(filename, 'rb');

    % Read the header
    header = fgets(fid);

    % Check if the file is P5 format
    if ~strcmp(header, 'P5\n')
        error('Not a P5 PGM file');
    end

    % Read the width, height, and max value
    w = fscanf(fid, '%d', 1);
    h = fscanf(fid, '%d', 1);
    maxval = fscanf(fid, '%d', 1);

    % Read the image data
    data = fread(fid, [w, h], 'uint8');

    % Close the file
    fclose(fid);

    % Convert to double and normalize to [0,1] range
    img = double(data') / maxval;
end

写入PGM图像：

function write_pgm(filename, img)
    % Open the file for writing
    fid = fopen(filename, 'wb');

    % Write the header
    fprintf(fid, 'P5\n');

    % Write the width, height, and max value
    [h, w] = size(img);
    fprintf(fid, '%d %d\n', w, h);
    fprintf(fid, '255\n');

    % Convert to uint8 and write the data
    data = uint8(round(img * 255));
    data = data';
    fwrite(fid, data, 'uint8');

    % Close the file
    fclose(fid);
end

注意，在这些示例代码中，我们假设PPM和PGM图像的最大值为255。如果您的图像最大值不同，请相应地修改代码。