Why is the line over imagesc not where I expected it to be?

Question

Larissa Perez 2023-3-31

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https://ww2.mathworks.cn/matlabcentral/answers/1938804-why-is-the-line-over-imagesc-not-where-i-expected-it-to-be

回答： Star Strider 2023-3-31

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Hi,

I'm trying to make a plot over an imagesc plot. Currently, it looks like this:

However, the red lines should be around the peak frequencies (close to 0.12 Hz).

The code is:

hold on
	hc=tplot(Tx, t, fs, opt);
	plot(t,UpperCs(:,1), 'LineWidth', 2, 'Color','k');
	plot(t,LowerCs(:,1), 'LineWidth', 2,'Color','r');
hold off

where tplot is a function that created the imagesc. UpperCs and LowerCs are vectors of the same length as t and with values around 0.12, as I expected. So I don't understand why the lines are being plotted near 1.

Many thanks!

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Answer 1

Star Strider 2023-3-31

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1938804-why-is-the-line-over-imagesc-not-where-i-expected-it-to-be#answer_1205944

The image functions such as imagesc reverse the y-axis direction.

Experiment with:

set(gca, 'YDir','normal')

to see if that will do what you want.

If it also reverses the image, then experiment with the flipud function on the matrix being plotted to see if that puts everhything the way you want it.