How to count no of black spots in a image??

clc
A5=imread('C:\Users\AMIT\Desktop\CB\sulphur\4-1.jpg');
imshow(A5);
background = imopen(A5,strel('disk',15));
I2 = A5- background;
figure, imshow(I2)
I3 = imadjust(I2);
figure, imshow(I3);
level = graythresh(I3); %Threshold the Image
bw = im2bw(I3,level);
C = imcrop(bw);
bw2 = bwareaopen(C,2);
figure, imshow(bw2)
cc = bwconncomp(bw2,8) %Identify Objects in the Image
P=cc.NumObjects;
SP=0.64/4;
defectdata = regionprops(cc, 'basic') %Compute Area of Each Object
DA = SP*[defectdata.Area];
[min_area, idx] = min(DA)  %Compute Area-based Statistics
[max_area, idx] = max(DA)
nbins = 20;                     %Create Histogram of the Area
figure, hist(DA,nbins)
title('Histogram of defect Area');
xlabel('Area of defect mm2');
ylabel('Number of defects')
Ylim ([0 50])
DA

[AMIT VERMA]

black dots marked in that red boundary is to be counted

[Wu Changjin Wu]

Hi, I have tried with the code, but it shows the error

"Error in number_of_blackspots (line 7)

I3 = imadjust(I2); "

do you know why and how to correct it?

[Walter Roberson]

Is the expected answer "3" or is it "lots" ?

[Walter Roberson]

imadjust() is only for grayscale images. Your I2 is RGB.

Answer 1

[Image Analyst]

You already compute it, in your "P" variable. You probably just didn't notice because of the poor choice of some of your variable names that are not descriptive at all.

See my Image Segmentation Tutorial:

Image Analyst's File Exchange

You might need to define just how small of a spot do you want to find.