how to reduce blob analysis rate in video so that object counting can happen every 3 seconds

I would like to do object counting but my code is checking for region of intereste every 1/30 second due to 30 frames per second because of this everytime it is detecting the object, any way i can solve this problem?

clc;
%% Setup of video

vidReader=vision.VideoFileReader('hvsstop2.mp4');
vidReader.VideoOutputDataType='double';
mywriter=VideoWriter('mymovie.mp4');
open(mywriter);
%% structural element
diskelem=strel('disk',2);
hblob=vision.BlobAnalysis('MinimumBlobArea',1500,'MaximumBlobArea',4000);
vidPlayer = vision.DeployableVideoPlayer;

while ~isDone(vidReader)

    %read frame
    vidframe=step(vidReader);

    %rgb to hsv color space
    I=rgb2hsv(vidframe);
    %htextins=insertText(I,'position',[20,20],'Color',[255 255 0],'Fontsize',30);


% Define thresholds for channel 1 based on histogram settings
channel1Min = 0.615;
channel1Max = 0.962;

% Define thresholds for channel 2 based on histogram settings
channel2Min = 0.000;
channel2Max = 0.058;

% Define thresholds for channel 3 based on histogram settings
channel3Min = 0.723;
channel3Max = 1.000;

% Create mask based on chosen histogram thresholds
sliderBW = (I(:,:,1) >= channel1Min ) & (I(:,:,1) <= channel1Max) & ...
    (I(:,:,2) >= channel2Min ) & (I(:,:,2) <= channel2Max) & ...
    (I(:,:,3) >= channel3Min ) & (I(:,:,3) <= channel3Max);
BW = sliderBW;

%using morphological operations
ibwopen=imopen(BW,diskelem);

%extract the blobs from the frame

[areaOut,centroidOut, bboxOut]=step(hblob,ibwopen);

%draw a box around detected objects
%ishape=insertShape(vidframe,'Rectangle',bboxOut,'ShapeColor','black');
%iannotate = insertObjectAnnotation(vidframe,"rectangle",bboxOut,'cardboard',TextBoxOpacity=0.9,FontSize=18);
iannotate_vid = insertObjectAnnotation(vidframe,"rectangle",...
    bboxOut,'versatilis',TextBoxOpacity=0.9,FontSize=30);

%paly in video player
vidPlayer(iannotate_vid);

writeVideo(mywriter,iannotate_vid);
end




%%release
release(vidReader)
release(hblob)
release(vidPlayer)
close(mywriter)
%release(ishape)

Answer 1

[Milan Bansal]

Hi Ashokraj

I understand that you wish to detect objects and count them every 3 seconds instead of 30 times in a single second as you are doing now.

Here an assumption has to be made that the frame rate of the video is 30 frames per second. So in 3 seconds there will be 90 frames. To resolve the issue, in the while loop, introduce a frame counter such that the object detection and counting will be done after every 90 frames. Here is how you can modify your code to achieve this:

clc;
%% Setup of video
vidReader = vision.VideoFileReader('hvsstop2.mp4');
vidReader.VideoOutputDataType = 'double';
mywriter = VideoWriter('mymovie.mp4');
open(mywriter);

%% Structural element
diskelem = strel('disk',2);
hblob = vision.BlobAnalysis('MinimumBlobArea',1500,'MaximumBlobArea',4000);
vidPlayer = vision.DeployableVideoPlayer;

frameCount = 0;
frameSkip = 90; % Number of frames to skip (30 FPS * 3 seconds)

while ~isDone(vidReader)
    frameCount = frameCount + 1;
    
    % Read frame
    vidframe = step(vidReader);
    
    % Process every 90th frame
    if mod(frameCount, frameSkip) == 0
        % RGB to HSV color space
        I = rgb2hsv(vidframe);

        % Define thresholds for channels based on histogram settings
        channel1Min = 0.615;
        channel1Max = 0.962;
        channel2Min = 0.000;
        channel2Max = 0.058;
        channel3Min = 0.723;
        channel3Max = 1.000;

        % Create mask based on chosen histogram thresholds
        sliderBW = (I(:,:,1) >= channel1Min) & (I(:,:,1) <= channel1Max) & ...
                   (I(:,:,2) >= channel2Min) & (I(:,:,2) <= channel2Max) & ...
                   (I(:,:,3) >= channel3Min) & (I(:,:,3) <= channel3Max);
        BW = sliderBW;

        % Using morphological operations
        ibwopen = imopen(BW, diskelem);

        % Extract the blobs from the frame
        [areaOut, centroidOut, bboxOut] = step(hblob, ibwopen);

        % Annotate the detected objects
        iannotate_vid = insertObjectAnnotation(vidframe, "rectangle", ...
            bboxOut, 'versatilis', TextBoxOpacity=0.9, FontSize=30);

        % Play in video player
        vidPlayer(iannotate_vid);
        
        % Write to video file
        writeVideo(mywriter, iannotate_vid);
    else
        % Play the unprocessed frame to keep video in sync
        vidPlayer(vidframe);
        writeVideo(mywriter, vidframe);
    end
end

%% Release resources
release(vidReader);
release(hblob);
release(vidPlayer);
close(mywriter);

Hope this helps!

[Image Analyst]

Instead of "if mod" why not just call read with the frame number of the one you want to extract and analyze?

thisFrame = read(vidReader, frame);

That way you're faster since you don't need to read and throw away frames you're not interested in.