How can I take a snapshot from USB camera and then analyze it?
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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.
1 Comment
Walter Roberson
on 27 Jun 2018
Make sure you install the GENTL support package; https://www.mathworks.com/hardware-support/gentl.html
Answers (2)
Florian Morsch
on 27 Jun 2018
Edited: Florian Morsch
on 27 Jun 2018
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);
2 Comments
Walter Roberson
on 27 Jun 2018
The GENTL package is perhaps more appropriate than the USB Webcams package for the Allied Vision devices.
PamunkeBoy
on 27 Jun 2018
4 Comments
Walter Roberson
on 27 Jun 2018
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
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