how to compare images in video processing?

this is my code

imaqhwinfo
info=imaqhwinfo('winvideo')
vid=videoinput('winvideo');
%Open Figure
hFigure=figure(1);
%set parameters for video
%Acquire only one frame each time
triggerconfig(vid,'Manual');
set(vid,'framespertrigger',1);
%Go on forever untill stopped
set(vid,'triggerrepeat',Inf);
%Get a grayscale image
set(vid,'ReturnedColorSpace','grayscale');
start(vid);
preview(vid);
for i=1:5
    trigger(vid);
    im=getdata(vid);
    figure,imshow(im(:,:,:,i));
end
stop(vid),delete(vid),clear(vid);

the problem is that i'm not getting multiple frames in a single figure,more over some times the program run and some times gives the error

?? Error using ==> imaqdevice.start at 19
 Multiple VIDEOINPUT objects cannot access the same device simultaneously.

why it happens and how can i solve it plz help

also m not getting the 4 frames ,it dispplay 3 figure windows out of which 2 is blank only 1 frame is showing

Answer 1

[Walter Roberson]

You have

im=getdata(vid);

so you are writing over all of "im". But on the next line you have

imshow(im(:,:,:,i));

which attempts to extract data only from the "i" slice of "im".

You need to be consistent: either write the data to a slice of "im", or overwrite all of "im" and show all of "im".

[Mehreen Hussain]

so should i write like this? imshow(im); it shows all the images separately in 5 different figure windows or should i write imshow(im(:,:,:,im); plz correct me ,i want to show all of im in one figure, thanks in advance,waiting for your kind reply

[Walter Roberson]

What result do you want? The images are shown in separate figure windows because you have the call to figure before your imshow()

[Mehreen Hussain]

i want all images in one figure