How can i make Compression Ration In this Case

I have this three Questions :

1)Read the Image ('flag.png')

2) convert it into ondex type and display it

3)Compression Ration ((Assignement))

Assignement:

HSI color space

HSV color space

YCbCr color space

I solve the first and second Question but How can i solve the third Question ?

figure

image_mat = imread('picture1.png');

imshow(image_mat)

[image_mat, cmap] = imread('picture1.png');

if isempty(cmap)

if ndims(image_mat) > 2

image_rgb = image_mat;

else

image_rgb = repmat(image_mat, [1 1 3]);

end

else

image_rgb = ind2rgb(image_mat, cmap);

end

imshow(image_rgb)