Segmentation of the microscope circle

I would like to remove the black area(background) of these images so that I can segment only the targetted region, which is the circle. Please help, thank you in advance.

[darova]

Did you try to binarize?

[Ramanaesh Rao]

Hi, yes I did but i lost the region of interest too.

Answer 1

[KALYAN ACHARJYA]

You can direct thresold the largest black area. Here the shown code is quite lengthy, but it is easier to understand.

bwImage=imbinarize(rgb2gray(rgbImage));
mask=bwareafilt(~bwImage,1);
R_data=rgbImage(:,:,1);
G_data=rgbImage(:,:,2);
B_data=rgbImage(:,:,3);
R_data(mask)=255;
G_data(mask)=255;
B_data(mask)=255;
result=cat(3,R_data,G_data,B_data);
figure,imshow(result);

[Ramanaesh Rao]

Hi Sir, I am getting Unrecognized function or variable 'rgbImage'

[KALYAN ACHARJYA]

You have to load the image first-

rgbImage=imread('Imagefilename.jpg');
%......................^Check the image file name & extention

%After this paste previous code 

[Ramanaesh Rao]

Thank you so much sir.