Graph plotting of number of red pixels vs number of images?

I would like to count the number of red pixels for every image in this folder. Next, plot the graph of no. of red pixels for each image vs the no. of images? How can this be done?

[Merged from duplicate question]

I would like to calculate the red pixel count for every image in this folder and then plot a graph of red pixel count vs the number of images. The red pixel count must correspond to the image no. This is my code.

%for loop 

clc;

clear;

close all;

fontSize=10;

myFolder='G:\FYP2\Time Frames\Frame 24';

if ~isdir(myFolder)

    errorMessage = sprintf('Error: The following folder does not exist:\n%s', myFolder);
    uiwait(warndlg(errorMessage));
    return;

end

filePattern = fullfile(myFolder, '*.png'); 

theFiles = dir(filePattern);

numberOfImages=length(theFiles);

red_counts = zeros(1, numberOfImages);

redCount=0;

for k=1:numberOfImages

fullFileName = fullfile(myFolder, theFiles(k).name);

thisImage=double(imread(fullFileName));

[rows, columns, numberOfColorBands] = size(thisImage); 

redBand=thisImage(:,:,1);

      %THRESHOLD LEVELS

redThresholdLow=215;

redThresholdHigh=255;

redMask=(redBand>=redThresholdLow) & (redBand<=redThresholdHigh);

      %Count pixels

redCount=sum(redMask(:)>0);

red_counts(k)=redCount;

end

plot(red_counts, numberOfImages, '-r*');

set(gca, 'xTickLabel', 1:1:numberOfImages);

ylabel('Red pixel count');

xlabel('Number of images');

[Sivakumaran Chandrasekaran]

http://in.mathworks.com/matlabcentral/answers/156454-howcan-count-just-red-pixels-in-matlab-image-proccessing

[Gee Cheng Mun]

I know to calculate the red pixels for the images. However, how can I display it as a graph of no. of red pixels vs no. of images?

Answer 1

[Walter Roberson]

Everything is written for you in http://uk.mathworks.com/matlabcentral/answers/263333-how-to-plot-an-intensity-graph#comment_334704 (you will have to view old comments there to see the code again.)

The key line is

     meets_red_threshold = thisimage(:,:,1) > 180 & thisimage(:,:,2) < 60 & thisimage(:,:,3) < 60;  %strong red compared to G or B ??

You need to alter this line to match your definition of what a "red pixel" is. Is a pixel "red" if it has any non-zero R component and the G and B components are 0? Visually you would find it difficult to distinguish such a pixel from black. If you plot [0.8 0.01 0.01] on the same line graph as [1 0 0] you are going to have trouble telling the two apart. So you need to define exactly what "red" means to you, as there is no scientific definition of what is "red" and what is not.

[Gee Cheng Mun]

But this time round, I would not be using the time. Instead, I will change to the number of images used. Like in this folder, I have 19 images. So my x-axis will be [1 2 3 ....19], whereby image 1 will have this number of red pixels. Then, when I got the number of red pixels for every image, I want plot it in the graph, like for 19 images, I want to have 19 points (different red pixel values) in the graph.

[Walter Roberson]

Then see the code before that in the earlier comment http://uk.mathworks.com/matlabcentral/answers/263333-how-to-plot-an-intensity-graph#comment_334697 and just replace the assignment of

t(K) = (K-1)/24;

with

t(K) = K;

[Gee Cheng Mun]

Thank you so much!:)