# How to find the x-axis of modulation transfer function of a gaussian curve in MATLAB?

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Manu Francis 2019 年 7 月 25 日
コメント済み: Cinzia Emmanuello 2020 年 3 月 13 日
I am trying to find modulation transfer function of a gaussian curve by using MATLAB. The gaussian curve is as below: x- axis is distance(form -15mm to 15mm) and y axis is count(Magnitude). I used the following code to find find fourier transfrom of gaussian curve.
FFT_y = fft(y); %take fourier transform
FF_mag = abs(FFT_y )/(length(FFT_y )); %find magnitude
FF_mag = (FF_mag-min(FF_mag))./(max(FF_mag)-min(FF_mag)); %normalize magnitude
I cropped FF_mag by using the following codes
FF_mag_nw = FF_mag(1:(length(FF_y)/32));
plot(FF_mag_nw);
I used 32 in above code to get main portion of graph and I got MTF plot as below: I am confused about X-axis. What will be the range of X-axis in per mm? Can anyone help me give an idea to calculate X-axis of MTF plot?

#### 1 件のコメント

Cinzia Emmanuello 2020 年 3 月 13 日
Dear Manu and whoever comes to this question while googling stuff,
I do not know in which field you are working in (you could have specified it) but anyway the x-axis is in the spatial frequency domain (line pairs/mm). The axis is not in mm anymore, you just applied a Fourier transformation.
Regards,
Cinzia

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### 回答 (1 件)

Nikhil Sonavane 2019 年 8 月 2 日
Referring to the last plot function used-
plot(FF_mag_nw);
The above command will plot FF_mag_nw which is a one-dimensional matrix against its row number as its x co-ordinate. X-axis in the plot will span from 1 to length(FF_y)/32. Hence, x-axis in your plot will only signify the total number of data points in FF_mag_nw.

#### 1 件のコメント

madhan ravi 2019 年 8 月 2 日
https://in.mathworks.com/help/matlab/ref/plot.html#description [see under plot(Y)]- exactly as mentioned in the doc, which is what Nikhil describes in his answer.

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