How to find sum of all pixel value of ROI in a grayscale image?

I am trying to draw a ROI of a grayscale image using imfreehand. After drawing this, I want to count all the intensity levels contained in this ROI. How can I do this?

Answer 1

[Walter Roberson]

http://www.mathworks.com/help/images/create-binary-mask-using-an-roi-object.html

Use the createMask method of the imfreehand object to create a binary mask. Suppose we call that mask . Then,

selected_values = YourImage(mask);
sum_of_selected = sum(selected_values);
count_intensity_values = length( unique(selected_values) );

[Jonathan Avesar]

So if I understood correctly:

selected_values contains the intensity values of all the pixels in YourImage that are within the ROI as defined by mask. Right?

sum_of_selected is then the sum of all the intensities

count_intensity_values is the number of unique intensity levels present within the select pixel values of selected_values

correct?

[Image Analyst]

Yes

[Jonathan Avesar]

Great thank you!

Answer 2

[Image Analyst]

See attached demo to freehand mask an image and find the drawn region's mean and centroid.

[Fahad Alharbi]

hi there, i am having a trouble using this demo. whenever i use another image (RGB) or different format (jpg) i get this error back :

"Error using iptassert (line 19) Size of I doesn't match size information found in the first input argument.

Error in regionprops>ParseInputs (line 1224) iptassert(isequal(sizeImage,size(I)), ...

Error in regionprops (line 205) [I,requestedStats,officialStats] = ParseInputs(imageSize, argOffset, varargin{:});

Error in freehand_masking_demo (line 66) measurements = regionprops(binaryImage, grayImage, ..." please help! thanks.

[Image Analyst]

You'd have to do it on each color channel one at a time:

% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);

[Fahad Alharbi]

thanks for the help dear sir. may I ask you one more question! how can I draw more then one mask at the same time ?

[Image Analyst]

Call imfreehand() multiple times in a loop. Each time, OR the image into the master mask binary image.

mask = mask | thisMask;

[Fahad Alharbi]

can I apply this demo on a folder of images insisted of one by one ? thanks again.

[Image Analyst]

Yes. See the FAQ for code samples http://matlab.wikia.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F