Videoinput function and bad quality image

Hi,

I am trying to use a usb microscope camera to take a series of photos of my samples. I use 'videoinput' and 'getsnapshot' to drive the camera and it takes a photo every few minute for a few hours. Some of the images taken by the camera are of good quality (see image 1 below) while some are of bad qualities with regions of over- and under-exposure. The occurance of bad images is around 1 in 3 but the frequency can vary. I want to know (1) if this is a common problem when using usb camera, (2) whether this is a hardware or software issue, (3) if it's possible to reduce its occurance by adjusting certain parameters in the camera setting.

I am attaching sections of my code at the end. Many thanks in advance!

clear

close all

clc

info = imaqhwinfo('winvideo')

for n = 1:100

vid = videoinput('winvideo',2,'YUY2_640x480');

set(vid,'ReturnedColorSpace','rgb');% convert from yuy2 to rgb

vid.FrameGrabInterval = 1; % time interval between captured frames

preview(vid)

start(vid)

I=getsnapshot(vid);

figure(1);

clf

newmap = rgb2gray(I);

imshow(newmap)

objects = imaqfind ;

delete(objects) ;

end