How to obtain the DCT ( discrete cosine transform )?

I want to btain the DCT on kids.tif image but I have these errors, What should I have do ?

RGB = imread ('kids.tif');
I = rgb2gray(RGB);
J= dct2 (I);
%taking logarithm
imshow (log(abs(J)),[]), colormap(jet(64)), colorbar

Now set values smaller than 10 in dct matrix to 0 and reconstruct the image using idct.

J(abs(J)<10) = 0;
K = idct2(J)/255;
imshow(K);

Error using rgb2gray>parse_inputs (line 81)
MAP must be a m x 3 array.

Error in rgb2gray (line 35)
X = parse_inputs(varargin{:});
Error using rgb2gray>parse_inputs (line 81)
MAP must be a m x 3 array.

Error in rgb2gray (line 35)
X = parse_inputs(varargin{:});

Answer 1

[Dishant Arora]

The image must be an indexed image not a RGB image. You shall use ind2gray.

[I, map]=imread('kids.tif');
I1=ind2gray(I,map);