Are you able to count the number of pixels in a 3D plot?

Question

sui zhi lau 2020-5-5

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https://ww2.mathworks.cn/matlabcentral/answers/523054-are-you-able-to-count-the-number-of-pixels-in-a-3d-plot

评论： sui zhi lau 2020-5-7

I am trying to find a way to count the number of red pixels in my moving plot and I was only able to find the number of white pixels in only at an angle. Would it be possible to count the total number of red pixels in a 3D plot?

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
xlabel('My x label') % Axis Labels
ylabel('My y label')
zlabel('My z label')
view([-37.5 30]) % standard 3D View
scale = 0.5; 
y = 1; % white percentage
%% range of results
d = 10; % Distance Between each point
nmesh = 3; % range
MagR = 0; % Magnetic Radius (MagR>nmesh = Strong, MagR<nmesh = weak, MagR = 0 = no Mag) 
niter = 200; % no. of jumps
[X,Y,Z] = meshgrid((-nmesh+1):nmesh-1); % create mesh
X = X * d;
Y = Y * d;
Z = Z * d;
%% random direction for X,Y,Z directions
dx = normrnd(0,1,[(size(X,1))^3 niter]);
dy = normrnd(0,1,[(size(X,1))^3 niter]);
dz = normrnd(0,1,[(size(X,1))^3 niter]);
%% Magnetised particles
c0 = nmesh;                         % center of magnetic field
for i = 1:size(dx,1)
    [ii,jj,kk] = ind2sub(size(X),i);   % row and column of force
    n = pdist2([ii jj kk],[c0 c0 c0]);         % distance to point
    if n < MagR                      % radius of magnetic force
        dx(i,:) = -cumsum(dx(i,:)*0+(jj-c0)/n);  % cosinus
        dy(i,:) = -cumsum(dy(i,:)*0+(ii-c0)/n);  % sinus
        dz(i,:) = -cumsum(dz(i,:)*0+(kk-c0)/n);
    end
end
cla
hold on
%% For Loop to plot 
for i = 1:niter-1
    X1 = X(:) + dx(:,i);
    Y1 = Y(:) + dy(:,i);
    Z1 = Z(:) + dz(:,i);
    plot3([X(:) X(:)]'+[dx(:,i+1) dx(:,i)]', ...
         [Y(:) Y(:)]'+[dy(:,i+1) dy(:,i)]',...
         [Z(:) Z(:)]'+[dz(:,i+1) dz(:,i)]','.-r','MarkerSize',5,'LineWidth',1)
    %p.MarkerSize = 10; % 6 is the default
    %p.LineWidth = 1; % 0.5 is the default
    pause(0.01)
    %% percentage readings  
    Image = getframe();
    K = sum(sum(rgb2gray(Image.cdata)==255));                                 
    percentageofwhite(y) = K/numel(rgb2gray(Image.cdata))*100;
    delete(findall(gcf,'type','text'))
    txt=text(0.0,0.95,sprintf('White Space = %0.3f%%',percentageofwhite(y)),'Units','normalized');
    y=y+1;
    %%
    xlim([-2*d 2*d]) % Axis limitsg
    ylim([-2*d 2*d])
    zlim([-2*d 2*d])
end
hold off
rotate3d on

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Mrutyunjaya Hiremath 2020-5-5

在 MATLAB Online 中打开

    plot3([X(:) X(:)]'+[dx(:,i+1) dx(:,i)]', ...
         [Y(:) Y(:)]'+[dy(:,i+1) dy(:,i)]',...
         [Z(:) Z(:)]'+[dz(:,i+1) dz(:,i)]','.-r','MarkerSize',5,'LineWidth',1)

According to this, you are drawing 125 pair red points in each iteration

sui zhi lau 2020-5-5

hi Mrutyunjaya,

thank you for the fast repliy! how did you get that value and how would i be able to compared the red pixels compared to the total white percentage to get a percentage of it then?

Ash

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Answer 1

darova 2020-5-5

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/523054-are-you-able-to-count-the-number-of-pixels-in-a-3d-plot#answer_430498

在 MATLAB Online 中打开

Can you calculate the volume manually?

dv = [dx(:,i+1)-dx(:,i) dy(:,i+1)-dy(:,i) dz(:,i+1)-dz(:,i)];
V = V + pi*R*sqrt(sum(dv.^2,2));        % volume of all lines

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darova 2020-5-6

在 MATLAB Online 中打开

Just to be sure: you want to calculate pixels or percentage (volume)? read/white = value?

Number of pixels differs, it depends on window size. Here is an example

f = figure(1);
plot([0 1 2],[0 1 1],'linew',2)       % plot some data
set(f,'position', [200 100 500 400])  % set small window
axis equal
fr = getframe;
A1 = fr.cdata;                        % small image
set(f,'position', [200 100 600 500])  % set larger window
fr = getframe;
A2 = fr.cdata;                        % large image
blue = @(A) A(:,:,1) < 10 & A(:,:,2) < 10 & A(:,:,3) > 240;
white= @(A) sum(A,3) > 250*3;
    % get colors from images
A1b = blue(A1);                       
A2b = blue(A2);                       
A1w = white(A1);
A2w = white(A2);
    % check if colors are correct
figure
subplot(211)
imshowpair(A1b,A2b,'montage')
subplot(212)
imshowpair(A1w,A2w,'montage')
sum(A1b(:))/sum(A1w(:))
sum(A2b(:))/sum(A2w(:))

Result

ans =
    0.0078
ans =
    0.0065

As you see the data remain the same, window size changes only. But ratio of blue/white changes

So can you tell what are you trying to calculate?

sui zhi lau 2020-5-6

Yes but what do i replace R with? For example i put my linewidth as 0.5, do i take my R as 0.5 ?

darova 2020-5-6

yes.

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Answer 2

Mrutyunjaya Hiremath 2020-5-6

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/523054-are-you-able-to-count-the-number-of-pixels-in-a-3d-plot#answer_430751

在 MATLAB Online 中打开

@ sui zhi lau,

Outside Loop

totalData = 0;
whitePixData = 40*40*40;

Inside Loop

redPixData(y) = sum(sqrt(((dx(:,i+1) - dx(:,i)).^2) + ((dy(:,i+1) - dy(:,i)).^2) + ((dz(:,i+1) - dz(:,i)).^2)));
totalData = totalData + redPixData(y);
percentageofred(y) = (totalData/whitePixData)*100;
txt=text(0.0,0.95,sprintf('White Space = %0.3f%%',percentageofred(y)),'Units','normalized');

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sui zhi lau 2020-5-7

在 MATLAB Online 中打开

I tried this but I think the totalData does not reflect the values correctly as for example,

Gives me a red percentage of 1614%

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
xlabel('My x label') % Axis Labels
ylabel('My y label')
zlabel('My z label')
view([-37.5 30]) % standard 3D View
nmesh = 5;
niter = 100;
scale = 0.5;
y = 1;
totalData = 0;
%%
d = 3;
[X,Y,Z] = meshgrid(0:nmesh-1); % create mesh
X = X * d
Y = Y * d
Z = Z * d
whitePixData = (d*(nmesh-1))^3;
%%
dx = normrnd(0,1,[nmesh^3 niter]);
dy = normrnd(0,1,[nmesh^3 niter]);
dz = normrnd(0,1,[nmesh^3 niter]);
cla
%plot3(X(:),Y(:),Z(:),'ob')         % plot starting points
hold on
%plot(X,Y,'k')                % plot grid
%plot(X',Y','k')
for i = 1:niter-1
    s=5;
    %s = normrnd(45,1)
    X1 = X(:) + dx(:,i);
    Y1 = Y(:) + dy(:,i);
    Z1 = Z(:) + dz(:,i);
    q = quiver3(X1, Y1, Z1, dx(:,i+1)-dx(:,i), dy(:,i+1)-dy(:,i),dz(:,i+1)-dz(:,i),'r')
    q.LineWidth = s;
    q.ShowArrowHead = 'off';
     %plot([X(:) X(:)]'+[dx(:,i+1) dx(:,i)]', ...
         %[Y(:) Y(:)]'+[dy(:,i+1) dy(:,i)]','.-r')
    pause(0.02)
    %% percentage readings  
    redPixData(y) = sum(sqrt(((dx(:,i+1) - dx(:,i)).^2) + ((dy(:,i+1) - dy(:,i)).^2) + ((dz(:,i+1) - dz(:,i)).^2)));
    totalData = totalData + redPixData(y);
    percentageofred(y) = (totalData/whitePixData)*100;
    delete(findall(gcf,'type','text'))
    txt=text(0.0,0.95,sprintf('Red Percentage = %0.3f%%',percentageofred(y)),'Units','normalized');
    y = y+1;
    xlim([0 d*nmesh])
    ylim([0 d*nmesh])
    zlim([0 d*nmesh])
end
hold off
rotate3d on

Mrutyunjaya Hiremath 2020-5-7

because, we are not considering the elimination of overlapping area.

sui zhi lau 2020-5-7

How would you consider with elimination of overlapping areas?

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Are you able to count the number of pixels in a 3D plot?

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Are you able to count the number of pixels in a 3D plot?

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