problem exporting figure to a single channel

after exporting the plotted figure to figure-01.png, the ,file dimenstion si already in 3 channels.

the code:

exportgraphics(figure(1),sprintf('fig_%02d.png', i),'Colorspace', 'gray')

A = imread("fig_01.png")

As result, the dimention of A = [h w 3]

[Catalytic]

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Answer 1

[Stephen23]

plot(rand(7,3))

F = getframe(figure(1));

I = im2gray(F.cdata);
imwrite(I,'test.png')
size(I)

ans = 1×2

420 561

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clearvars

J = imread('test.png');
size(J)

ans = 1×2

420 561

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