How can I take a snapshot from USB camera and then analyze it?

On my previous work, I was trying to take an image from a file and find the centroids of the images. However, I am having trouble taking the snapshot and then having MATLAB save the image so then I can analyze it for the centroids of the dots. Is there any way this can be done?

 % clear, clc
% establish video input 
cam=videoinput('gentl',1,'Mono8');
%take snapshot 
preview(cam) 
triggerconfig(cam, 'manual');
snapshot=getsnapshot(cam); 
%Display image 
im=imagesc(snapshot)
im=max(im,[],3);
% Segment blobs 
bw=imclose(im<20,strel('disk',5)); binaryImage = imfill(im, 'holes');
% Cenroids of individual blobs 
RP=regionprops(bw,'Centroid'); N=numel(RP); C=zeros(N,2); 
for i=1:N, 
C(i,:)=RP(i).Centroid; 
end
% Centroid of all blobs 
C_net=regionprops(double(bw),'Centroid'); 
C_net=C_net.Centroid; 
figure imshow(bw) hold on plot(C(:,1),C(:,2),'or','MarkerSize',10,'LineWidth',2) plot(C_net(:,1),C_net(:,2),'*g','MarkerSize',10,'LineWidth',2)
%Calculating the distance formula
D=sqrt(((C(4,1)) - (C(2,1))).^2 + ((C(4,2)) - (C(2,2))).^2);
formatSpec = 'Distance of top row is %4.2f pixels\n'; fprintf(formatSpec,D)
D2=sqrt(((C(3,1)) - (C(1,1))).^2 + ((C(3,2)) - (C(1,2))).^2);
formatSpec = 'Distance of bottom row is %4.2f pixels\n'; fprintf(formatSpec,D2)
closePreview(cam);

Specifically the im=max function appears to not be working. My goal is to get MATLAB to be able to take the snapshot image and determine the centroids between them.

[Walter Roberson]

Make sure you install the GENTL support package; https://www.mathworks.com/hardware-support/gentl.html

Answer 1

[Florian Morsch]

First install the support package "MATLAB Support Package for USB Webcams" ( https://de.mathworks.com/matlabcentral/fileexchange/45182-matlab-support-package-for-usb-webcams )

Then you can do something like this:

cam = webcam(); % This chooses the first connected webcam. If you have multiple use webcam(2), webcam(3) etc.

Snapshot = snapshot(cam);

image(Snapshot);
imwrite(Snapshot, 'SomeName.png'); % To save it to another location you can do something like
                                     'C:/User/MATLABPictures/SomeName.png')

This will take a snapshot and save it as .png file to your current folder. Or you can work with the snapshot, e.g.:

cam = webcam();
cam.Resolution = '800x600';
Snapshot = snapshot(cam);
SnapshotGray = rgb2gray(Snapshot);

[PamunkeBoy]

I am currently using a Allied Vision Webcam, will this work with it?

[Walter Roberson]

The GENTL package is perhaps more appropriate than the USB Webcams package for the Allied Vision devices.

Answer 2

[PamunkeBoy]

I have actually now been able to save the image that has been captured and can upload it to MATLAB for analysis. I now want to be able to cycle this code so that each time it performs this task it saves a new image instead of just replacing the file. Can this be done? Perhaps if I modify "saveas" in my code

 clear, clc
% establish video input
cam=videoinput('gentl',1,'Mono8');
%take snapshot
preview(cam)
closepreview(cam)
triggerconfig(cam, 'manual');
snapshot=getsnapshot(cam);
%display image
figure,imshow(snapshot)
saveas(gcf,'MyFigure.bmp')
% Get the image
im=imread('MyFigure.bmp');
im=max(im,[],3);
% Segment blobs
bw=imclose(im<40,strel('disk',5));
binaryImage = imfill(im, 'holes');
% Cenroids of individual blobs
RP=regionprops(bw,'Centroid');
N=numel(RP);
C=zeros(N,2);
for i=1:N, C(i,:)=RP(i).Centroid; end
%Layout of Image
figure
imshow(bw)
hold on
plot(C(:,1),C(:,2),'or','MarkerSize',10,'LineWidth',2)
%Calculating the distance formula
D=sqrt(((C(4,1)) - (C(2,1))).^2 + ((C(4,2)) - (C(2,2))).^2);
formatSpec = 'Distance of top row is %4.2f pixels\n';
fprintf(formatSpec,D)
D2=sqrt(((C(3,1)) - (C(1,1))).^2 + ((C(3,2)) - (C(1,2))).^2);
formatSpec = 'Distance of bottom row is %4.2f pixels\n';
fprintf(formatSpec,D2)

[Walter Roberson]

for image_number = 1 : 100    %to process 100 images
  snapshot = getsnapshot(cam);
  filename = sprintf('framein_%04d.bmp', image_number);
  saveas(gcf, filename)
  im = imread(filename)
  ...
end

However, it you would then be analyzing the figure frame and axes frame and so on. You already have just the image itself in snapshot . It would seem to make more sense to use

for image_number = 1 : 100    %to process 100 images
  snapshot = getsnapshot(cam);
  filename = sprintf('framein_%04d.bmp', image_number);
  imwrite(snapshot, filename);
  im = snapshot;
  ...
end

[PamunkeBoy]

Thank you!!! I was also wondering is there a way to start the loop every time by pressing a key so it wont just cycle through?

[Walter Roberson]

image_number = 0;

while true
  key = input('Return to continue, Q to quit: ', 's');
  if strcmpi(key, 'q'); break; end
  snapshot = getsnapshot(cam);
  image_number = image_number + 1;
  filename = sprintf('framein_%04d.bmp', image_number);
  imwrite(snapshot, filename);
  im = snapshot;
  ...
end

[PamunkeBoy]

Thank you for all of your help Walter!