How can i filter the spectrogram colours and take as matrix?

Hello, I am trying to change spectrogram matrix colours. I am writing audio and music recognition system based on Spectrogram.

function spectrogram_graph(audiofile_name)
[y,fs]=audioread(audiofile_name);
fprintf("Amount of Fs is:%d \n",fs)
specgram(y);
xlabel("Samples")
ylabel("Normalized Frequency (x pi radians/sample)")
colormap gray
c=colorbar;
c.Label.String="Powerfrequency dB(rad/sample)";

end

I have this table from this function:

I need to filter, for example: Higher than -40dB will be white and lowers will be black. I need to recieve this as matrix with only ones and zeros. Thats why i am using grayscale.

Firsty, I couldnt filter and change the colours of the spectrogram.

Secondly, I couldnt obtain 2D matrix of the spectrogram.

Can you help me please guys, best wishes

Altemur

[Mathieu NOE]

hello

so if I understand right, the spectrogram should be converted to 0 and 1 only based on threshold value -40 dB ?

this is how I modified your code and the outcome of it :

[y,fs]=audioread('test_voice.wav');
fprintf("Amount of Fs is:%d \n",fs)
[yo,fo,to] = specgram(y(:,1)); % NB the amplitude of spectrogram is not in dB but in linear scale
yo = abs(yo);
figure(1),imagesc(to,fo,yo);axis('xy');
colormap jet
c=colorbar;

% apply threshold to make binary image
threshold = 0.01*max(yo,[],'all'); % equivalement in linear scale to -40 dB of max (in dB) )
spg_thres = zeros(size(yo));
ind = find(yo>threshold);
spg_thres(ind) = 1;
figure(2),imagesc(to,fo,spg_thres);axis('xy');
xlabel("Samples")
ylabel("Normalized Frequency (x pi radians/sample)")
colormap gray
c=colorbar;

[Altemur Çelikayar]

Thats exactly what i need. How can i obtain this spectrogram img as matrix from top left to right bottom? Thanks a lot :D

[Mathieu NOE]

the data are stored in array spg_thres

[Altemur Çelikayar]

You are amazing. Thanks a lot <3

[Mathieu NOE]

You're welcome !