how to calculate the no. of pixel?

hi all,

i done convert gray image to binary image. but how i want to calculate the how much no pixel in red circle as picture attached??

my image name is spect128x128

I15 = dicomread('spect128x128', 'frame', 15);
T15 = graythresh(level);
BW15 = imbinarize(I15,T15);
figure
imshowpair(I15, BW15, 'montage')

Answer 1

[Ameer Hamza]

See bwconncomp(): https://www.mathworks.com/help/images/ref/bwconncomp.html. It returns a struct. You can check the number of elements in PixelIdxList property to count the pixels.

[mohd akmal masud]

but it seems like calculate all the white pixel. not only in red circel right?

[Ameer Hamza]

Yes, it will detect 4 regions. You can select the one which is largest.

[mohd akmal masud]

ok thank you.

now i have this coding as above.

then do you know how to know the location for example [59x1 double it self]?

CC = 
  struct with fields:
    Connectivity: 8
       ImageSize: [130 130]
      NumObjects: 4
    PixelIdxList: {[6×1 double]  [22×1 double]  [35×1 double]  [59×1 double]}
    

[Ameer Hamza]

You can just access it as a cell array

CC.PixelIdxList{4} % 4 indicate 4th element

It will give linear indexes of pixel. To get row and column index, read my answer here: https://www.mathworks.com/matlabcentral/answers/645283-how-to-know-the-location-pixel#answer_542043

[mohd akmal masud]

ok, thank you so much sir.

then how to to fill the color in every object. lets say i want fill blue color in object no.4?