How do I fix an error when regionprops finds no blob?

In my binary image, there is no blob/ 0 pixel /white pixel. It shows me an error.

Here is my code:

 Obj = regionprops(binaryImage, gambarAsliParkir1, 'Area' , 'BoundingBox');
 [~, numbersOBJECT] = bwlabel(binaryImage);
 clear P1;
    for i=1:numbersOBJECT
        area= Obj(i).Area;
        P1(i)=area; %#ok<AGROW>
    end

[KALYAN ACHARJYA]

Provide the data binaryImage & gambarAsliParkir1??

[Aaron Abel]

Yes, the explaination of the syntax is:

"stats = regionprops(___,I,properties) returns measurements for the set of properties specified by properties for each labeled region in the image I. The first input to regionprops (BW, CC, or L) identifies the regions in I."

I can get the blobs from gambarAsliParkir1 which is grayscale image. binaryImage is the binary image from gambarAsliParkir1 which have been processed.

[Walter Roberson]

What error message are you getting?

With you clearing P1 and iterating 1:numberOfObjects, if there are no objects, you would leave P1 undefined. Perhaps you should be using

P1 = zeros(1, numbersOBJECT);

Or you could just use

P1 = [Obj.Area];

which would extract all of the Area values without using any loop.

[Aaron Abel]

I forgot to add the last syntax.

Obj = regionprops(binaryImage, gambarAsliParkir1, 'Area' , 'BoundingBox');
 [~, numbersOBJECT] = bwlabel(binaryImage);
 clear P1;
    for i=1:numbersOBJECT
        area= Obj(i).Area;
        P1(i)=area; %#ok<AGROW>
    end 
pixel1=sum(P1);

the error is

Undefined function or variable 'P1'.

Yes, as you said, P1 is undefined.

I need to sum the number of the pixels and find the largest object, then I can crop it, if there are objects in binaryImage.

Thank you very much, I found it succesful that I replaced the loop with

P1 = [Obj.Area];

At the moment, I don't need

bwlabel

anymore.

But, I find this problem

    Obj = regionprops(binaryImage, gambarAsliParkir1, 'Area' , 'BoundingBox');
    clear ruangParkir1;
    P1=[Obj.Area];
    pixel1=sum(P1);
    pixel1max=max(P1);
    P1=P1==pixel1max;
    ObjBB = Obj(P1).BoundingBox; 
    Image1= imcrop(gambarAsliParkir1, ObjBB);

This is the error.

Insufficient number of outputs from right hand side of equal sign to satisfy assignment.

Error in untitled>pushbutton3_Callback (line 677)

ObjBB = Obj(P1).BoundingBox;

[Walter Roberson]

Your code is ambiguous in the case that the two largest blobs have exactly the same area; what do you want to do in that case?

Answer 1

[Image Analyst]

Label it before

[labeledImage, numberOfRegions] = bwlabel(binaryImage);
props = regionprops(labeledImage, gambarAsliParkir1, 'Area' , 'BoundingBox');
allAreas = [props.Area] % Vector with list of all the areas.
pixel1 = sum(allAreas)    % Sum them up

No for loop needed.

You really don't even need to call bwlabel, though it's often useful to get a labeled image if you want to do something like filtering on computer/derived measurements (like circularity), or to give unique colors to individual blobs with label2rgb() which makes it easy to determine if nearby blobs are connected or not. So you could do

props = regionprops(binaryImage, gambarAsliParkir1, 'Area' , 'BoundingBox');
allAreas = [props.Area] % Vector with list of all the areas.
pixel1 = sum(allAreas)    % Sum them up

[Aaron Abel]

Thank you for answering, I appreciate it. Your information is useful. I will try it.