Create a new matrix that contains indices for values that are larger than X

Task 2: Use the matrix that you previously created for the values of green
(G) Create a new matrix that contains
indices for green values that are larger than the intensity threshold,
(S) The size of this matrix should be
“number of pixels” x “number of pixels”. Clearly label this new matrix. Create a new matrix with size “number of pixels” x “number of
pixels x 3”, where the matrix obtained in the previous step is “duplicated”
along the 3 dimensions. This generates a “mask” that tells us whether or
not the RGB content at any pixel met the criteria in the previous task (i.e.,
whether the green channel intensity was greater than the threshold).

Task 4: Display in figure 3 a new image where the background from the
original image has been replaced with a white background. Hint: the color
white implies an intensity of 255 for all three channels, R, G, and B