20060606-Batch processing

原文：http://blogs.mathworks.com/steve/2006/06/06/batch-processing/

Step 1: Get a list of filenames

If you use the dir function with an output argument, you get back a structure array containing the filenames, as well as other information about each file.

Let's say I want to process all files ending in .jpg:

files = dir('*.jpg')

Let's look at the details of the  files struct array for a couple of these files.

files(1)
files(end)

Step 2: Determine the processing steps to follow for each file

There are four basic steps to follow for each file:

1. Read in the data from the file.
2. Process the data.
3. Construct the output filename.
4. Write out the processed data.

Here's what my read and processing steps looked like:

rgb = imread('IMG_0175.jpg');  % or rgb = imread(files(1).name);
rgb = rgb(1:1800, 520:2000, :);
rgb = imresize(rgb, 0.2, 'bicubic');

You have many options to consider for constructing the output filename. In my case, I wanted to use the same name but in a subfolder:

output_name = ['cropped\' files(1).name] % Use fullfile instead if you want
                                         % multiplatform portability

You might use something like this if you want to change image formats.

input_name = files(1).name
[path, name, extension] = fileparts(input_name)
output_name = fullfile(path, [name '.tif'])

Step 3: Put everything together in a for loop

Here's my complete batch processing loop:

files = dir('*.JPG');
for k = 1:numel(files)
   rgb = imread(files(k).name);
   rgb = rgb(1:1800, 520:2000, :);
   rgb = imresize(rgb, 0.2, 'bicubic');
   imwrite(rgb, ['cropped\' files(k).name]);
end