如何在matlab中读取指定文件夹中的图像?

myPath= 'C:\Users\Prienka\Documents\MATLAB\frames'; 
a =dir(fullfile(myPath,'*.png'));
a(1).name
a(end).name
Im1 = imread(a(1).name);
Im2 = imread(a(end).name);
Im1 = rgb2gray(Im1);
Im2 = rgb2gray(Im2);
hn1 = imhist(Im1)./numel(Im1); %initial pixel postion
hn2 = imhist(Im2)./numel(Im2); %final pixel position
d = sum(sqrt(hn2-hn1).^2); 
d=sprintf('%.0f',d);
obj = VideoReader('traffic.mp4')
x=obj.FrameRate
velocity=d/x;
velocity=sprintf('%.0f',velocity)
if velocity >= 63
    msgbox('SPEED EXCEEDED' ) 
end
myPath= 'C:\Users\Prienka\Documents\MATLAB\fram