One of easiest solution is to use Image batch processor app. Type
in the command window. In the app press the load images button, specify the folder. In the function name specify the name of the function you want to apply to all of the images (for example see the function below) and click process selected. You can also use Parallel processing if you have Parallel Processing Toolbox. It will automatically process all the images. In the end, you can export all the data to the workspace or save to another folder.
function out = batchImage(im)
out.gray = rgb2gray(im);
out.hist = histcounts(gray, 0:255);
end
This approach reduces the chances of making an error. And if you are still interested in the code, press the downward arrow on export button and select Generate Function.
