MATLAB: Undefined function ‘dyaddown’ for input arguments of type ‘uint8’.

downsampleImage Processing Toolboxinput argumentsundefinedunit8Wavelet Toolbox

Getting the error:
Undefined function 'dyaddown' for input arguments of type 'uint8'.
Code is:
   %Clear command window.
clc;
    %Clear workspace.
clear;
    %Load the Lena file.
RGB = imread ('Lena.tiff'); 
    %Display the result of the conversion.
figure, imshow(RGB);
    %Convert RGB image to YCbCr Components.
YCbCr = rgb2ycbcr(RGB);
    %Isolate Y. 
Y = YCbCr(:,:,1);
    %Isolate Cb. 
Cb = YCbCr(:,:,2);
    %Isolate Cr. 
Cr= YCbCr(:,:,3);
    %downsample
dem = dyaddown(Cb,1,'m') % Downsample rows and columns
                        % with odd indices.
Why is this? How to I fix it?
Many thanks.

Best Answer

I've never heard of dyaddown(). If you want to subsample Cb to get only the odd indexes and end up with an image 1/4 as big, do this:
dem = Cb(1:2:end, 1:2:end);  % Extract only odd indexes.
For even indices, do this:
dem = Cb(2:2:end, 2:2:end);  % Extract only even indexes.
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