matlab通过fopen实现读取和写入PPM图像P3 和P6的功能

以下是通过`fopen`在MATLAB中实现读取和写入PPM图像P3和P6的示例代码：

读取P3格式的PPM图像：

fid = fopen('image.ppm', 'r');
if fid == -1
    error('Unable to open file.');
end

% Read file header
fgetl(fid); % Skip magic number
fgetl(fid); % Skip comment
dims = sscanf(fgetl(fid), '%d %d', [1, 2]);
max_val = sscanf(fgetl(fid), '%d', 1);

% Read image data
data = fscanf(fid, '%d %d %d', [3, dims(1)*dims(2)]);
data = data';

% Close the file
fclose(fid);

% Reshape the data into a 3D matrix
img = reshape(data, [dims(2), dims(1), 3]);
img = uint8(img);

写入P3格式的PPM图像：

img = imread('image.png');
img = double(img);

% Open file for writing
fid = fopen('image.ppm', 'w');
if fid == -1
    error('Unable to open file.');
end

% Write file header
fprintf(fid, 'P3\n');
fprintf(fid, '# Created by MATLAB\n');
fprintf(fid, '%d %d\n', size(img, 2), size(img, 1));
fprintf(fid, '%d\n', 255);

% Write image data
for i = 1:size(img, 1)
    for j = 1:size(img, 2)
        fprintf(fid, '%d %d %d ', img(i, j, 1), img(i, j, 2), img(i, j, 3));
    end
    fprintf(fid, '\n');
end

% Close the file
fclose(fid);

读取P6格式的PPM图像：

fid = fopen('image.ppm', 'rb');
if fid == -1
    error('Unable to open file.');
end

% Read file header
fgetl(fid); % Skip magic number
fgetl(fid); % Skip comment
dims = sscanf(fgetl(fid), '%d %d', [1, 2]);
max_val = sscanf(fgetl(fid), '%d', 1);

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

% Close the file
fclose(fid);

% Convert to uint8
img = uint8(data);

写入P6格式的PPM图像：

img = imread('image.png');

% Open file for writing
fid = fopen('image.ppm', 'wb');
if fid == -1
    error('Unable to open file.');
end

% Write file header
fprintf(fid, 'P6\n');
fprintf(fid, '# Created by MATLAB\n');
fprintf(fid, '%d %d\n', size(img, 2), size(img, 1));
fprintf(fid, '%d\n', 255);

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

% Close the file
fclose(fid);

请注意，这些示例代码仅适用于基本的PPM图像格式，您可能需要根据您的具体需求进行修改。此外，该代码仅支持8位图像数据。如果您的图像数据是16位或32位，请相应地进行修改。