I want to find the distance of each cross from the center blue cross when the mat with grid lines is moving i.e. it will be a video.

The aim of this project is to calculate distance of each cross from the center cross in terms of (x,y) pixel location. I have applied blob analysis method to firstly locate each cross but when im applying thresholding i am unable to remove all the other unwanted white area which is making it very difficult simultaneously i have also applied image segmentation but when the crosses are moving it is not detecting it both of my codes are presented below.

%Thresholdind Code

%% Load Sample Frames

v = imread('WIN_20240502_14_38_36_Pro.jpg');

subplot(1,3,1)

imshow(v);

% Convert RGB image to chosen color space

I = rgb2hsv(v);

% Define thresholds for channel 1 based on histogram settings

channel1Min = 0.188;

channel1Max = 0.000;

% Define thresholds for channel 2 based on histogram settings

channel2Min = 0.172;

channel2Max = 1.000;

% Define thresholds for channel 3 based on histogram settings

channel3Min = 0.391;

channel3Max = 0.712;

% 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;

% Close mask with disk

% radius = 13;

% decomposition = 0;

% se = strel('disk', radius, decomposition);

% BW = imclose(BW, se);

% Close mask with disk

radius = 2;

decomposition = 0;

se = strel('disk', radius, decomposition);

BW = imdilate(BW, se);

figure;

subplot(2,1,1)

imshow(BW)

radius = 2;

d = 0;

se = strel('disk',radius,d);

BW= imclose(BW,se)

subplot(2,1,2)

imshow(BW)

%% Blob Analysis using Segmentation

hblob = vision.BlobAnalysis('MinimumBlobArea',200,'MaximumBlobArea',1000);

[objarea,objcent,bboxOut]= hblob(BW)

%% Annotate images

Image= insertShape(v,'rectangle',bboxOut,'linewidth',4);

figure

subplot(1,2,1)

imshow(Image)

%Image Segmentation Code

v = vision.VideoFileReader('WIN_20240502_15_10_30_Pro.mp4');

v.VideoOutputDataType = 'double';

hblob = vision.BlobAnalysis('MinimumBlobArea',200,'MaximumBlobArea',5000);

% Create video player object

vidPlayer = vision.DeployableVideoPlayer;

while ~isDone(v)

vidframe = step(v);

% Convert RGB image into L*a*b* color space.

X = rgb2lab(vidframe);

foregroundInd = [319346 319347 319348 319349 319350 319351 319352 320047 320063 320064 320783 321487 321502 322207 322220 322927 323647 323648 323658 324368 324377 325088 325097 325809 325817 326529 327250 327970 328691 329412 329417 330132 330136 330852 330856 331573 331574 331576 332294 332295 333014 333734 333735 334456 335174 335177 335893 336612 336618 337326 337327 337328 337329 337330 337331 337340 337341 338061 338782 339504 339505 339506 339507 516253 516973 517693 518414 518438 519135 519155 519156 519157 519855 519856 519875 520577 520592 520593 521298 521311 522018 522020 522030 522741 522749 523462 523463 523464 523468 524184 524187 524514 525625 525627 525954 525955 526293 526314 526345 526346 526347 527013 527032 527034 527067 527397 527417 527418 527420 527421 527733 527753 527784 527788 527789 528117 528118 528119 528136 528453 528454 528469 528471 528472 528504 528509 528839 528855 529174 529191 529223 529230 529560 529573 529574 529575 529894 529909 529910 529942 529952 530281 530282 530283 530292 530615 530629 530662 530672 531004 531008 531009 531010 531011 531336 531348 531382 531393 531725 531726 531727 531728 532056 532066 532067 532101 532114 532115 532445 532446 532447 532786 532818 532820 532836 533162 533163 533164 533165 533169 533502 533504 533538 533557 533880 533881 533890 533891 533892 534217 534221 534256 534257 534599 534613 534938 534940 534976 535317 535318 535334 535335 535659 535660 535689 535694 535695 536036 536055 536056 536378 536409 536410 536411 536413 536754 536755 536778 537097 537473 537474 537500 537501 537502 537816 537821 538192 538222 538223 538535 538912 538944 539254 539255 539264 539632 539664 539665 539973 539985 540352 540353 540693 540706 540707 541412 541428 542131 542148 542149 542851 542871 543591 544312 715310 716753 716754 717475 718195 718196 718917 718918 718938 719638 719639 719640 719657 720360 720362 720377 721084 721095 721096 721804 721815 722525 722526 722527 722535 723247 723254 723255 723968 723973 724689 724690 724692 724693 725411 725412 726129 726130 726131 726132 726847 726848 726853 726854 727567 727574 728284 728285 728286 728295 729004 729720 729721 729722 730439 731157 731876 733313 733315 734032 734750 734752 ];

backgroundInd = [14 82 857 862 1570 2307 2998 3750 4331 5770 5824 5866 5913 5915 5917 6490 6557 6568 8081 8649 8807 9531 9535 10089 10258 11701 12422 13142 14582 15848 18727 21780 24487 28087 31135 31687 36007 38334 38887 41047 45367 46972 49687 52567 55447 59767 61365 62647 64807 68407 70567 72157 73447 82807 88706 93607 99498 100807 104407 104535 109447 115330 116647 125287 127563 135367 135480 140519 145447 149154 160567 165708 170647 177224 183605 190902 198722 204579 217537 230495 243452 253529 263606 269365 272963 276561 280157 283033 285191 286630 287347 287349 288752 288753 288754 288756 288760 288765 288768 288771 288773 288777 288782 288784 289470 290186 290904 294501 296657 298095 298813 298814 299523 299525 299529 299530 299532 308903 308908 308912 308916 308917 308919 308928 308932 308939 308942 308948 308952 308954 308959 308963 308966 308968 308973 308981 308983 308988 308993 308994 308996 308998 309615 309616 309617 309620 309621 309641 309645 309723 309729 309735 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L = superpixels(X,4708,'IsInputLab',true);

% Convert L*a*b* range to [0 1]

scaledX = prepLab(X);

BW = lazysnapping(scaledX,L,foregroundInd,backgroundInd);

% Close mask with line

length = 16.000000;

angle = 0.000000;

se = strel('line', length, angle);

BW = imclose(BW, se);

%% Blob Analysis

hblob = vision.BlobAnalysis('MinimumBlobArea',200,'MaximumBlobArea',5000);

[objarea,objcent,bboxOut]= hblob(BW)

% Annotate images

Image = insertShape(vidframe, 'rectangle', bboxOut);

% numObj = length(objarea);

% Image = insertText(Image, [20 20], int32(numObj), 'TextColor', [255 255 0], 'FontSize', 30);

% Display annotated frame

step(vidPlayer, Image);

end

% Clean up

release(v);

release(hblob);

function out = prepLab(in)

% Convert L*a*b* image to range [0,1]

out = in;

out(:,:,1) = in(:,:,1) / 100; % L range is [0 100].

out(:,:,2) = (in(:,:,2) + 86.1827) / 184.4170; % a* range is [-86.1827,98.2343].

out(:,:,3) = (in(:,:,3) + 107.8602) / 202.3382; % b* range is [-107.8602,94.4780].

end

Answer 1

[VINAYAK LUHA]

Hi Shaherbano,

I understand that -

1. You have video featuring a checkerboard with some green and red cross markings and,
2. You are using "blob analysis" in MATLAB to calculate the distance of these cross markings from the central blue cross marking.
3. However, you are encountering difficulties in removing the unwanted white areas.

Follow the below steps to remove the white areas -

• Use the MATLAB "Color Segementer App" to select an appropriate range for the HSV threshold for the colours. I found the following thresholds for green, red, and blue colors to work effectively in this case:

%HSV thresholds for green, red, and blue colors in [Low, High] format
greenThreshold = [0.237 0.505; 0.082 1; 0.0 0.765]; 
redThreshold = [0.9 1; 0.25 1; 0.25 1]; 
blueThreshold = [0.5 0.7; 0.19 0.85; 0 1]; 

• Additionally, you can impose an area threshold, say, 150px² on the detected "regionprops" to filter out the small, irrelevant regions.

Following are the masks obtained using the above outlined steps

Next, you can proceed with calculating and showing the distances between the red,green cross markings and the blue cross marking, you may use the MATLAB 'pdist2' function for calculating the distance followed by the "text" and "line" functions for showing the distance.

Here is the final result based on the above suggestions:

For more details on the functions you may use to implement your workflow, refer to the following MATLAB documentation.

• "regionprops" -https://www.mathworks.com/help/images/ref/regionprops.html"
• "line" function -www.mathworks.com/help/matlab/ref/line.html
• "pdist2" for calculating distance between a coordinate pair -https://www.mathworks.com/help/stats/pdist2.html
• "text" function -https://www.mathworks.com/help/matlab/ref/text.html

I hope you can incorporate these suggestions into your code and extend it to calculating and showing distances in videos.

Regards,

Vinayak

[shaherbano zaidi]

Thankyou Vinayak.