Select area in picture and send information about r,g,b

Hello,

I need to select an area on my picture and i want to have informations about r,g,b.

Someone can help me, please ?

Thanks!

Answer 1

[KSSV]

If I is an image you canget:

R = I(:,:,1) ;
G = I(:,:,2) ;
B = I(:,:,3) ; 

You can select your required area using imcrop, imfreehand.

[Abbass SAYEGH]

yes it's an image

But if for example i need to get theses information about colors, can i have save them on txt file ?

Thank you

[KSSV]

Yes..you can write the data into text file. Read about fprintf, saveas, writematrix.

Answer 2

[Image Analyst]

What information do you need? For example, you can mask it and get the means and area. See attached demo.

You can get the histogram.

No idea what you want really. See my File Exchange for some ideas.

[Abbass SAYEGH]

i want to select an area on my picture? and after to have informations about it (like r,g,b) and to save these informations in a txt file

[Image Analyst]

Then combine the masking demo with the RGBXY to CSV demo.

[Abbass SAYEGH]

ok i cant open theses files

Can you send show me just the files with the lines of code ?

[Image Analyst]

Strange. Did you right click and say "Save link as..."?

Here are the demos.

First, here is RGBXY_to_CSV.m

% Take an RGB Image and write all the pixel info to a csv file in the form [R, G, B, X, Y].
% It will have as many rows as pixels in the image, and have those 5 columns.
% Initialization steps.
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.
format long g;
format compact;

% Have user browse for a file, from a specified "starting folder."
% For convenience in browsing, set a starting folder from which to browse.
startingFolder = 'C:\Program Files\MATLAB\R2018a\toolbox\matlab\imagesci'; % or 'C:\wherever';
if ~exist(startingFolder, 'dir')
	% If that folder doesn't exist, just start in the current folder.
	startingFolder = pwd;
end
% Get the name of the file that the user wants to use.
defaultFileName = fullfile(startingFolder, '*.*');
[baseFileName, folder] = uigetfile(defaultFileName, 'Select a file');
if baseFileName == 0
	% User clicked the Cancel button.
	return;
end
fullFileName = fullfile(folder, baseFileName)

% Read in the image.
rgbImage = imread(fullFileName);
% Display the image.
imshow(rgbImage);
% Put up statusbar to let you mouse around over it and see r, g, b, and (x, y)
impixelinfo();
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0.2, 0.2, 0.8, 0.8]);
drawnow; % Force immediate screen repaint.

% Get x and y for all pixels.
[rows, columns, numberOfColorChannels] = size(rgbImage)

if numberOfColorChannels == 1
	% This is not an RGB image.
	promptMessage = sprintf('This is not an RGB image\nDo you want to Continue processing as grayscale, \nMake RGB,\nor Quit processing?');
	titleBarCaption = 'Continue?';
	buttonText = questdlg(promptMessage, titleBarCaption, 'Grayscale', 'Make RGB', 'Quit', 'Continue');
	if contains(buttonText, 'Quit')
		return;
	elseif contains(buttonText, 'RGB')
		% Convert to RGB.
		rgbImage = cat(3, rgbImage, rgbImage, rgbImage);
		[rows, columns, numberOfColorChannels] = size(rgbImage);
	else
		% Leave as grayscale.
	end	
end

[x, y] = meshgrid(1:columns, 1:rows);
% Extract the individual red, green, and blue color channels.
% Need to cast to double or else x and y will be clipped to 255 when we concatenate them.
if numberOfColorChannels == 1
	% Leave as gray scale.
	% Get array listing [r, g, b, x, y].  Using (:) will turn all the 2-D arrays into column vectors.
	output = [rgbImage(:), x(:), y(:)];
else
	redChannel = double(rgbImage(:, :, 1));
	greenChannel = double(rgbImage(:, :, 2));
	blueChannel = double(rgbImage(:, :, 3));
	% Get array listing [r, g, b, x, y].  Using (:) will turn all the 2-D arrays into column vectors.
	output = [redChannel(:), greenChannel(:), blueChannel(:), x(:), y(:)];
end
% Get the output filename - same as input file name but with .csv extension.
[folder, baseFileNameNoExtension, extension] = fileparts(fullFileName);
baseFileName = [baseFileNameNoExtension, '.csv'];
% folder = pwd; % Change to current folder.
outputFileName = fullfile(folder, baseFileName);
% Write output to CSV file.
message = sprintf('Please wait...\n    Writing data to CSV file:\n        %s', outputFileName);
fprintf('%s\n', message);
csvwrite(outputFileName, output);

% Let user know we're done.
fprintf('Done!\n    Wrote data to CSV file:\n        %s\n', outputFileName);
% Open up
promptMessage = sprintf('Done!\n\nWrote data to CSV file:\n%s\n\nDo you want me to it now?', outputFileName);
titleBarCaption = 'Open?';
buttonText = questdlg(promptMessage, titleBarCaption, 'Yes - open it', 'No, do not open it', 'Yes - open it');
if contains(buttonText, 'No,')
	return;
end
winopen(outputFileName);

and here is freehand_masking_demo.m

% Demo to have the user freehand draw an irregular shape over a gray scale image.
% Then it creates new images:
% (1) where the drawn region is all white inside the region and untouched outside the region,
% (2) where the drawn region is all black inside the region and untouched outside the region,
% (3) where the drawn region is untouched inside the region and all black outside the region.
% It also (4) calculates the mean intensity value and standard deviation of the image within that shape,
% (5) calculates the perimeter, centroid, and center of mass (weighted centroid), and
% (6) crops the drawn region to a new, smaller separate image.

% Change the current folder to the folder of this m-file.
if(~isdeployed)
	cd(fileparts(which(mfilename)));
end
clc;	% Clear command window.
clear;	% Delete all variables.
close all;	% Close all figure windows except those created by imtool.
imtool close all;	% Close all figure windows created by imtool.
workspace;	% Make sure the workspace panel is showing.
fontSize = 16;

% Read in a standard MATLAB gray scale demo image.
folder = fileparts(which('cameraman.tif')); % Determine where demo folder is.
baseFileName = 'cameraman.tif';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
	% File doesn't exist -- didn't find it there.  Check the search path for it.
	fullFileName = baseFileName; % No path this time.
	if ~exist(fullFileName, 'file')
		% Still didn't find it.  Alert user.
		errorMessage = sprintf('Error: %s does not exist in the search path folders.', fullFileName);
		uiwait(warndlg(errorMessage));
		return;
	end
end
grayImage = imread(fullFileName);
[rows, columns, numberOfColorChannels] = size(grayImage);
imshow(grayImage, []);
axis on;
title('Original Grayscale Image', 'FontSize', fontSize);
set(gcf, 'Position', get(0,'Screensize')); % Maximize figure.

% Ask user to draw freehand mask.
message = sprintf('Left click and hold to begin drawing.\nSimply lift the mouse button to finish');
uiwait(msgbox(message));
hFH = imfreehand(); % Actual line of code to do the drawing.
% Create a binary image ("mask") from the ROI object.
binaryImage = hFH.createMask();
xy = hFH.getPosition;

% Now make it smaller so we can show more images.
subplot(2, 4, 1);
imshow(grayImage, []);
axis on;
drawnow;
title('Original gray scale image', 'FontSize', fontSize);

% Display the freehand mask.
subplot(2, 4, 2);
imshow(binaryImage);
axis on;
title('Binary mask of the region', 'FontSize', fontSize);

% Label the binary image and computer the centroid and center of mass.
labeledImage = bwlabel(binaryImage);
measurements = regionprops(binaryImage, grayImage, ...
    'area', 'Centroid', 'WeightedCentroid', 'Perimeter');
area = measurements.Area
centroid = measurements.Centroid
centerOfMass = measurements.WeightedCentroid
perimeter = measurements.Perimeter

% Calculate the area, in pixels, that they drew.
numberOfPixels1 = sum(binaryImage(:))
% Another way to calculate it that takes fractional pixels into account.
numberOfPixels2 = bwarea(binaryImage)

% Get coordinates of the boundary of the freehand drawn region.
structBoundaries = bwboundaries(binaryImage);
xy=structBoundaries{1}; % Get n by 2 array of x,y coordinates.
x = xy(:, 2); % Columns.
y = xy(:, 1); % Rows.
subplot(2, 4, 1); % Plot over original image.
hold on; % Don't blow away the image.
plot(x, y, 'LineWidth', 2);
drawnow; % Force it to draw immediately.

% Burn region as white into image by setting it to 255 wherever the mask is true.
% burnedImage = grayImage;
% burnedImage(binaryImage) = 255;
% Mask the image using bsxfun() function to multiply the mask by each channel individually.  Works for gray scale as well as RGB Color images.
burnedImage = bsxfun(@plus, grayImage, 255);
% Display the image with the mask "burned in."
subplot(2, 4, 3);
imshow(burnedImage);
axis on;
caption = sprintf('Masked white inside region');
title(caption, 'FontSize', fontSize);

% Burn region as black into image by setting it to 255 wherever the mask is true.
% Mask the image using bsxfun() function to multiply the mask by each channel individually.  Works for gray scale as well as RGB Color images.
burnedImage = bsxfun(@times, grayImage, cast(~binaryImage, 'like', grayImage));
% Display the image with the mask "burned in."
subplot(2, 4, 4);
imshow(burnedImage);
axis on;
caption = sprintf('Masked black inside region');
title(caption, 'FontSize', fontSize);

% Mask the image white outside the mask, and display it.
% Will keep only the part of the image that's inside the mask, white outside mask.
whiteMaskedImage = grayImage;
whiteMaskedImage(~binaryImage) = 255;
subplot(2, 4, 5);
imshow(whiteMaskedImage);
axis on;
title('Masked white outside region', 'FontSize', fontSize);

% Mask the image outside the mask (make it black outside the white mask region), and display it.
% Will keep only the part of the image that's inside the mask, zero outside mask.
% Mask the image using bsxfun() function to multiply the mask by each channel individually.  Works for gray scale as well as RGB Color images.
blackMaskedImage = bsxfun(@times, grayImage, cast(binaryImage, 'like', grayImage));
subplot(2, 4, 6);
imshow(blackMaskedImage);
axis on;
title('Masked black outside region', 'FontSize', fontSize);
% Calculate the mean
meanGL = mean(blackMaskedImage(binaryImage));
sdGL = std(double(blackMaskedImage(binaryImage)));

% Put up crosses at the centroid and center of mass.
hold on;
plot(centroid(1), centroid(2), 'r+', 'MarkerSize', 30, 'LineWidth', 2);
plot(centerOfMass(1), centerOfMass(2), 'g+', 'MarkerSize', 20, 'LineWidth', 2);

% Now crop the image.
leftColumn = min(x);
rightColumn = max(x);
topLine = min(y);
bottomLine = max(y);
width = rightColumn - leftColumn + 1;
height = bottomLine - topLine + 1;
croppedImage = imcrop(blackMaskedImage, [leftColumn, topLine, width, height]);
% Display cropped image.
subplot(2, 4, 7:8);
imshow(croppedImage);
axis on;
title('Cropped image', 'FontSize', fontSize);

% Put up crosses at the centroid and center of mass.
hold on;
plot(centroid(1)-leftColumn, centroid(2)-topLine, 'r+', 'MarkerSize', 30, 'LineWidth', 2);
% text(centroid(1)-leftColumn + 20, centroid(2)-topLine-20, 'Centroid', 'Color', 'r');
plot(centerOfMass(1)-leftColumn, centerOfMass(2)-topLine, 'g+', 'MarkerSize', 20, 'LineWidth', 2);
% text(centroid(1)-leftColumn + 20, centroid(2)-topLine+20, 'Weighted Centroid', 'Color', 'g');

% Report results.
message = sprintf('Mean value within drawn area = %.3f\nStandard deviation within drawn area = %.3f\nNumber of pixels = %d\nArea in pixels = %.2f\nperimeter = %.2f\nCentroid at (x,y) = (%.1f, %.1f)\nCenter of Mass at (x,y) = (%.1f, %.1f)\nRed crosshairs at centroid.\nGreen crosshairs at center of mass.', ...
meanGL, sdGL, numberOfPixels1, numberOfPixels2, perimeter, ...
centroid(1), centroid(2), centerOfMass(1), centerOfMass(2));
msgbox(message);

[Abbass SAYEGH]

Good morning,

Thanks for the help

If i want to do in many pictures, it's possible to an automatic command to have Image's analyzing ?

Thanks

[Image Analyst]

We still need to figure out why you were not able to save the files directly from your browser and I had to paste them into the message body. Can you answer my questions about it above?

For your "Answer" here that you posted (which is actually a new question), see the FAQ: https://matlab.fandom.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

[Abbass SAYEGH]

To answer your question, i use the company's computer. So i can't download file on internet

Ok i will check that

thank you

[Abbass SAYEGH]

Hello,

I don't have an exemple which show me how to do automatic command.

Can i have an exemple about that ?

Thanks

[Walter Roberson]

dinfo = dir('*.png');
filenames = {dinfo.name};
nfiles = length(filenames);
for K = 1 : nfiles
    thisfile = filenames{K};
    thisimage = imread(thisfile);
    revimage = 255-thisimage;
    imshow(revimage)
    title(thisfile);
    pause(1);
end

[Abbass SAYEGH]

Hello,

I used your 2 programs for my project, but i can't save the datas (pixels) when i select the region for the process

Can you help me ?

Thank you

[Image Analyst]

Abbass, add a call to imwrite():

folder = pwd; % or 'C:/wherever you want'
fullFileName = fullfile(folder, 'Cropped Image.png'); % Whatever you want to call it...
imwrite(croppedImage, fullFileName);

[Abbass SAYEGH]

but the informations are : the values of r,g,b on the console

it's the same thing i have to do ?

[Abbass SAYEGH]

Hello everyone,

I need, when i select the area for the process, to perform thresholding and detect edges, and the to delete them out of my process.

Someone can help me ?

Thanks

[Image Analyst]

Sure. Follow these steps:

1. Create mask with drawfreehand()
2. Threshold image binaryImage = grayImage < someThresholdValue
3. Detect edges with either (A) edgeImage = edge(grayImage) if you want edges on the gray scale image, or (B) with boundaries = bwboundaries(binaryImage) if you want edges on the binaryImage and then burn the edges into the binaryImage.
4. Erase edges with edgeImage(mask) = false.

[Abbass SAYEGH]

Can you send me the lines of code please ? It will be better to understand

thanks

[Abbass SAYEGH]

Hello,

Everyone can help me please ? I need lines of code able to do automatic command. The command is : when i select an area on the image, i want to open all the files with the same extension for the process ?

I don t have idea about it

thanks

[Image Analyst]

Don't you think it's better for you to understand if you work through it yourself?

[Image Analyst]

See the FAQ: https://matlab.fandom.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

[Abbass SAYEGH]

I work on my code for the automatic process but i dont know why i have this error : Undefined function 'isfolder' for input arguments of type 'char'.

Error in Auto_process (line 7)

if ~isfolder(myFolder)

can someone help me? I need to display all my xlsx or csv files in my folder

my code is here :

% Specify the folder where the files lives
myFolder = 'C:\Users\p107215\Desktop\matlab\projet';
% Check to make sure that folder actually exists. Warn the user if it
% doesn't
if  ~isfolder(myFolder)
    errorMessage = sprintf('Error: The following folder does not exist:\n%s\nPlease specify a new folder.', myFolder);
    uiwait(warndlg(errorMessage));
    myFolder = uigetdir(); % Ask for a new one.
    if myFolder == 0
         % User clicked Cancel
         return;
    end
end

% Get a list of all files in the folder with the desired file name pattern.
myFolder = 'C:\Users\p107215\Desktop\matlab\projet';
filePattern = fullfile(myFolder,'.csv'); % Change to whatever pattern you need
thefiles = dir(filePattern);
for k = 1 : length(thefiles)
    baseFileName = thefiles(k).name
    fulleFileName = fullfile(thefiles(k).folder, baseFileName);
    fprintf(1, 'Now reading %s \n', fullFileName);
    % Now we can do wathever we want with this file name
    imageArray = xlsread(fullFileName)
    imageshow(imageArray);
    drawnow
end

[Walter Roberson]

Your MATLAB is too old to have isfolder() . Use isdir() instead.

[Abbass SAYEGH]

but i dont know, nothing happened when the program run ? why ?

[Abbass SAYEGH]

Can someone help me with this problem ?

[Image Analyst]

Sure but we don't know exactly what you want. We gave you code for tracing out some area on the image and getting all the values and the mean value in the drawn area. We also gave you code for processing a sequence of images. But we don't really know what "I need lines of code able to do automatic command. The command is : when i select an area on the image, i want to open all the files with the same extension for the process ? " means. Can you give us a step-by-step process for what you want to do, like:

1. Interactively browse for an image and Get the filename.
2. Read it in the selected image.
3. Display error if user picks a gray scale image instead of a color image.
4. Display the color image.
5. User draws some irregular region on it.
6. Get individual color channels.
7. Get mean gray level for each of the color channels inside the drawn region.
8. Save these values and filename.
9. Enter a loop where we process all (other) files that have the same extension as the first image that was chosen
10. Inside the loop, repeat steps 2 through 8

etc.

Unless you do that your request is so vague and imprecise that if we do something (like we already have), you'll just say it's not what you want. So please give a step-by-step recipe of what you want to do.

[Abbass SAYEGH]

Thank you for your answer.

So, what i need exactly.

1. Browse my folder and find all my xlsx files
2. Open these xlsx files like image
3. When i opened them, i want to select an area
4. when i select this area, i want to put the values of pixels (r,g,b) on new xlsx file
5. Calculate the mean of these values and put it on new xlsx file
6. Do the same process for the rest of the files

If you want more informations tell me about that.

thanks

[Image Analyst]

You forgot to attach a sample Excel workbook, probably because you ignored the posting guidelines when you posted. Here, you can read them here: https://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer

What form is the image in in Excel? A 2-D matrix? A N-by-3 list of (x,y,graylevel)?

[Abbass SAYEGH]

Hello

my Image is a N-by-3 list of (x,y,graylevel)

You want to see my Excel Workbook ? It's like other excel file.

[Abbass SAYEGH]

Can I have help for my question ? or i cant ?

[Walter Roberson]

my Image is a N-by-3 list of (x,y,graylevel)

Is the file "complete", in the sense that every possible x and y combination appears? Or are some not listed -- for example are the locations that are zero not listed ? Are the x and y regularly spaced? Are they positive integers that start from 1 ? Should it be considered scattered information, samples of the actual surface with the other locations on the grid to be interpolated based upon the points that are present?

• Browse my folder and find all my xlsx files

We gave you code for that.

• Open these xlsx files like image

readtable() or readmatrix() or xlsread(). But then you have to arrange the list of data into an image, and to do that we need to know the answers to the questions I asked above.

• When i opened them, i want to select an area

A fixed area? If so then imcrop() or index the image. A variable area? If so then imfreehand(). Image Analyst showed you how to do that in https://www.mathworks.com/matlabcentral/answers/592150-select-area-in-picture-and-send-information-about-r-g-b#comment_1005523 and also attached a demonstration program in one of his other answers. Or use https://www.mathworks.com/help/images/ref/roipoly.html roipoly()

• when i select this area, i want to put the values of pixels (r,g,b) on new xlsx file

If you used imfreehand() then use createmask https://www.mathworks.com/help/images/ref/imroi.createmask.html to get a binary selection matrix. If you used roipoly() then it returns a binary selection matrix directly. If you somehow have a list of coordinates that bound the selection region then poly2mask() https://www.mathworks.com/help/images/ref/poly2mask.html

Now use find() with two outputs on the mask to get a list of rows and column numbers where the mask is set. The row numbers are your y coordinates. The column numbers are your x coordinates. Do not make the mistake of using the rows as your x coordinates!!

Now use the logical mask to index your grayscale image. The result will be a vector of image values, in the same order that find() returned its values.

Put the x, y, and values together into an N x 3 array.

Now writematrix() or writetable() or xlswrite() the data out.

• Calculate the mean of these values and put it on new xlsx file

mean() the vector of values referred to above. writematrix() or writetable() or writecell() or xlswrite() the data out.

• Do the same process for the rest of the files

We gave you the code for that.

If you are wanting to put the mean values all in the same xlsx file, then I recommend that you do not write the mean values into a file inside the loop. I recommend that you instead record the values in arrays, and then do a single write at the end. Keeping track of the current position inside an xlsx file to be able to write at the "end" of it is a nuisance best avoided (and writing only once would be considerably more efficient.)

Can I have help for my question ? or i cant ?

Ummm.. you know we are volunteers, and that we have other things going on in our lives, like answering other questions, or sleeping, or our jobs, or relaxing because we are worn out from answering lots of questions? The majority of the active volunteers are in North America, and your post about the file format and your prodding for additional assistance were during the middle of the night in North America.

[Image Analyst]

I'll ask you the same question you asked us "Can I have help for my question ? or i cant ?"

I specifically and directly asked you to attach one of your Excel workbooks, and instead of simply attaching one, you said "It's like other excel file." Come on - make it easy for us to help you not hard! You're basically saying to me "I don't want to spend a few seconds to attach my workbook but I expect you to write code to read in some image, then write out the x,y,grayLevel values, in order to create some sample image." Why are you wanting me to go through all that? No, sorry but I won't. If you won't spend the time to attach it and make it easy for us to help you, then I won't spend my time either.

We can't just write the whole thing for you, but there are people who would gladly do so. They are here. Please contact them and they'd be happy to do it all for you and deliver a turnkey system, or train you throughout the process while you do it.

We non-Mathworks volunteers generally provide some help if we can do it within a few minutes (which we've already spent). If it would be more than that, we can provide code snippets or refer you to the FAQ or other places (File Exchange) for code, which we've done. Try to make an effort with the code snippets you now know about and make a stab at creating your program. I mean the code in the FAQ is basically half the program you'd need. Here, I adapted the FAQ code a little for you to give you a start.

% Specify the folder where the files live.
myFolder = 'C:\Users\yourUserName\Documents\My Pictures';
% Check to make sure that folder actually exists.  Warn user if it doesn't.
if ~isfolder(myFolder)
	errorMessage = sprintf('Error: The following folder does not exist:\n%s\nPlease specify a new folder.', myFolder);
	uiwait(warndlg(errorMessage));
	myFolder = uigetdir(); % Ask for a new one.
	if myFolder == 0
		% User clicked Cancel
		return;
	end
end
% Get a list of all files in the folder with the desired file name pattern.
filePattern = fullfile(myFolder, '*.xls*'); % Change to whatever pattern you need.
theFiles = dir(filePattern);
for k = 1 : length(theFiles)
	baseFileName = theFiles(k).name;
	fullFileName = fullfile(theFiles(k).folder, baseFileName);
	fprintf(1, 'Now reading %s\n', fullFileName);
	% Now do whatever you want with this file name,
	% such as reading it in as an image array with imread()
	imageArray = xlsread(fullFileName);
	% Find size in the last row.  Form is [x, y, grayLevel]
	columns = imageArray(end, 1); % Max X
	rows = imageArray(end, 2); % Max Y
	grayLevels = imageArray(:, 3);
	% Reshape into rectangle:
	imageArray = reshape(imageArray, rows, columns);
	imshow(imageArray);  % Display image.
	drawnow; % Force display to update immediately.
	
	% Call roipoly() or drawfreehand() to get a mask
	% I'm sure you can figure this out.
	
	% Get row, column for pixels in the mask
	[r, c] = find(mask);
	% Make new array
	output = zeros(length(r), 3);
	for kk = 1 : length(r)
		output(kk, 1) = c(kk);
		output(kk, 2) = r(kk);
		output(kk, 3) = imageArray(r(kk), c(kk), kk);
	end
        % Create Excel filename by appending _output
	excelFullFileName = strrep(lower(fullFileName), '.xls', '_output.xls');
	writematrix(output, excelFullFileName);
end

Why not try it? Good luck.