how to apply dct code on each color plane of an RGB image

 i understand how to separate a 3d color image into its rgb color planes written below but how to apply the dct to each plane? 

 % Extract the individual red, green, and blue color channels.

R= rgbImage(:, :, 1);

G= rgbImage(:, :, 2);

B= rgbImage(:, :, 3);

Answer 1

[David Young]

Rtrans = dct2(R);

etc.