MATLAB: How to give the spectrogram a colormap option and save it as it is when plotted

spectrogram

Here's my code
% feature_size :[257,7]
figure(1)
imagesc( some_image_smaple )
colormap(jet(128))
set(gca,'YDir','normal')
above code shows like this :
But when I try to save this feature, if I use the code below,
cmap=jet(128);
imwrite( some_image_sample, cmap, 'sample.jpg');
it shows like this :
I'm not sure what's wrong, but I'd appreciate it if you let me know.

Best Answer

Hi,
In general, “imwrite” save an image which is of the format RGB. So, there is necessity to change the image displayed by “imagesc” (which scales the image such that the full range of colormap) in order to save the same image. This change is such that the normalized image array with colormap indices should be passed into imwrite function.
The following code solves your issue.
figure(1)
im = imagesc(some_image_matrix);
colormap(jet(128))
set(gca,'YDir','normal')
cmap=jet(128);
img_o = im.CData; % im is an image object and im.CData gives the image matrix
min_ = min(img_o(:));
max_ = max(img_o(:)); 
imgr = round((single((im.CData)-min_)./max_-min_)*128); % normalized and converted into colormap indices
img1 = ind2rgb(imgr,cmap); % Converts the indexed array into rgb format
imwrite(flip(img1), 'sample.jpg'); % flip is used as 'imagesc' inverts the axes when displayed
Related Question