time domain to frequency domain conversion

I have a image of signal in time domain taken from a DSO in .jpeg form. I need to convert this signal into frequency domain and obtain the graph of frequency versus amplitude. I used grabit command and obtained the data from the image. Then i converted it using a program which i found on mathworks website and i got the X axis and Y axis values. When i plot frequency graph,the frequency what i am getting is very less (0.2-0.5 Hz). How can i correct it? please help me...

Answer 1

[Abhishek Ballaney]

https://in.mathworks.com/help/matlab/ref/fft2.html