Expert Answer:
Here's an example of how to use graythresh on an indexed image in MATLAB:
% Load an indexed image
[X,map] = imread('example.tif');
% Convert the indexed image to a grayscale image
I = ind2gray(X,map);
% Use graythresh to determine the threshold level
level = graythresh(I);
% Convert the grayscale image to a binary image using the threshold level
BW = imbinarize(I,level);
% Display the binary image
imshow(BW)
In this example, the ind2gray function is used to convert the indexed image X and its colormap map to a grayscale image I. Then, graythresh is used to determine the threshold level for the grayscale image I. Finally, imbinarize is used to convert the grayscale image I to a binary image BW using the threshold level.
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