How to optimize imagesc plot with pixel labels to get a faster frame grab for creating a .avi

Hello,

The code below is a portion of a larger code that I am using to analyze pixel by pixel temperature in different zones within the field of view. I typically have between 3000-9000 induvidual frames of data which are each 32X31, for below I used a random set of data with 4010 frames. Right now this currently grabs frames at a rate of about 1 frame per second, as I have so many frames this takes on order of hours to grab all of the frames. I would like to be able to create the .avi much faster, but I believe the slow down is due to the creation of F, specfically the text() pixel labels. The code runs through 50 layers without the added pixel lables in about 8 seconds, but it takes almost a minute with the labels.

Is there a better way to apply the pixel by pixel labels to an imagesc plot or a way to make my current code more efficient?

%Creating custom color map
gyr_map=[
    0,1,0;0.02,1,0;0.04,1,0;0.06,1,0;0.08,1,0;0.10,1,0;0.12,1,0;0.14,1,0;0.16,1,0;0.18,1,0;...
    0.20,1,0;0.220,1,0;0.24,1,0;0.27,1,0;0.29,1,0;0.31,1,0;0.33,1,0;0.35,1,0;0.37,1,0;0.39,1,0;...
    0.41,1,0;0.43,1,0;0.45,1,0;0.47,1,0;0.49,1,0;0.51,1,0;0.53,1,0;0.55,1,0;0.57,1,0;0.59,1,0;...
    0.61,1,0;0.63,1,0;0.65,1,0;0.67,1,0;0.69,1,0;0.71,1,0;0.73,1,0;0.76,1,0;0.78,1,0;0.80,1,0;...
    0.82,1,0;0.84,1,0;0.86,1,0;0.88,1,0;0.90,1,0;0.92,1,0;0.94,1,0;0.96,1,0;0.98,1,0;1,1,0;...
    1,1,0;1,0.98,0;1,0.96,0;1,0.94,0;1,0.92,0;1,0.90,0;1,0.88,0;1,0.86,0;1,0.84,0;1,0.82,0;...
    1,0.80,0;1,0.78,0;1,0.76,0;1,0.73,0;1,0.71,0;1,0.69,0;1,0.67,0;1,0.65,0;1,0.63,0;1,0.61,0;...
    1,0.59,0;1,0.57,0;1,0.55,0;1,0.53,0;1,0.51,0;1,0.49,0;1,0.47,0;1,0.45,0;1,0.43,0;1,0.41,0;...
    1,0.39,0;1,0.37,0;1,0.35,0;1,0.33,0;1,0.31,0;1,0.29,0;1,0.27,0;1,0.24,0;1,0.22,0;1,0.20,0;...
    1,0.18,0;1,0.16,0;1,0.14,0;1,0.12,0;1,0.10,0;1,0.08,0;1,0.06,0;1,0.04,0;1,0.02,0;1,0,0];

%Creating a random set of data within standard temperature range
Random_multi = randi([40 70],32,31,4010);
[multi_r,multi_c, multi_frames] = size(Random_multi);
x_cor=repmat(1:multi_c,multi_r,1);  %x-cordinates
y_cor=(repmat(1:multi_r,multi_c,1))';%y-cordinates
n_frames=4010;

%Creating a column vector of stage labels
Stage1_labels=repmat({'Stage 1:'},[32080 1]);
Stage1_labels_str = convertCharsToStrings(Stage1_labels);
Stage2_labels=repmat({'Stage 2:'},[32080 1]);
Stage2_labels_str=convertCharsToStrings(Stage2_labels);
Stage3_labels=repmat({'Stage 3:'},[32080 1]);
Stage3_labels_str=convertCharsToStrings(Stage3_labels);
Stage4_labels=repmat({'Stage 4:'},[32080 1]);
Stage4_labels_str=convertCharsToStrings(Stage4_labels);
stage=vertcat(Stage1_labels_str,Stage2_labels_str,Stage3_labels_str,Stage4_labels_str);

%Creating a column vector of induvidual line numbers
Layer_number_rand=[1:128320]';

%Iterating through each frame of the multidimensional array & getting movie frame
for i=1:1:n_frames
    lineindex=i*32;
    
figure(20)
imagesc(Random_multi(:,:,i))
grid on
colorbar
colormap(gyr_map)
caxis([40 70])
str_title=strcat('Temperature: ',stage(lineindex),num2str(Layer_number_rand(lineindex)));   % Setting title with Temp:stage name:Line number
title(str_title)
str=strcat(' Frame: ',num2str(i));      
annotation('textbox',[0 0 .1 .1],'String',str,'EdgeColor','k')  %Creating left corner box to display the frame number

% Generate pixel Labels
t = num2cell(Random_multi(:,:,i)); % extact temperature values into cells
t = cellfun(@num2str, t, 'UniformOutput', false); % convert to string
% % Draw Image and Label Pixels
text(x_cor(:), y_cor(:), t, 'HorizontalAlignment', 'Center','Fontsize',5)

F(i)=getframe(figure (20));
clf(figure (20))
end
Tempobj=VideoWriter('Random Data.avi');

%Tempobj.FrameRate=2;
open(Tempobj);
for kk=1:length(F)
    writeVideo(Tempobj,F(kk));
end
close(Tempobj)

Answer 1

[darova]

Move every possible operations outside the for loop

Some exaplanations

Simple example

clc,clear

    % create new object 'plot' for each frame
tic
x = linspace(0,20);
for i = 1:100    
    y = sin(x+i/10);
    plot(x,y)
    drawnow
end
toc

    % create 'plot' object once and change the data for each frame
tic
h = plot(0,0);
for i = 1:100    
    y = sin(x+i/10);
    set(h,'xdata',x,'ydata',y)
    drawnow
end
toc

results

Elapsed time is 0.984396 seconds.           % new object
Elapsed time is 0.344684 seconds.           % change the data only

See attached script

[HarleyR]

Thank You! I knew that I needed to not create a new object each time but I wasn't sure how to accomplish that, your attached code was exactly what I needed. At this point is the speed only constrained by Matlab iself? I am wondering if there anything I can do to manipulate my input data to speed it up?

[darova]

• At this point is the speed only constrained by Matlab iself? I am wondering if there anything I can do to manipulate my input data to speed it up?

What do you mean?