Hi Minho, This is because when you call CWT with no output arguments, the CWT uses a logarithmic frequency axis, it actually uses log to the base 2 as explained in the help.
"The frequency or period axis in the scalogram uses a log2 scale."
The wavelet transform most appropriately uses logarithmic scaling on the frequency axis because of the dilation property of the wavelet. So if you use a logarithmic axis
[wt,f,coi] = cwt(kobe,1);
imagesc((1:numel(kobe))./60,log2(f*1e3),abs(wt));
ax = gca;
ytick = str2num(cell2mat(ax.YTickLabel));
ax.YTickLabel = num2str(2.^ytick);
set(gca,'Ydir','normal');
xlabel('Time(mins)')
ylabel('Frequency[mHz]')
You will see it is the same. In your example, you are using a linear frequency axis. That is what accounts for the difference in what you see.
