Needing to get the coordinates of the illuminated pixels

Hi, I'm trying to get the coordinates of the pixels in the lit area of greyImg. Is this possible?

 RGB=imread('image_0.png');
greyImg = rgb2gray(RGB);

Answer 1

[Thorsten]

You can define a threshold by visual inspection to separate the lit from the unlit pixels to get a binary image.

mythreshold = 0.55;
BW = im2bw(I, mythreshold);

idx = BW == 1; % logical index
idx = find(BW); % numerical index

Answer 2

[Antonio Cebrián]

sorry but it doesn't work. I have got an empty matrix