how to correlation plots from image

I = imread('Figure_1.png');

J = medfilt2(I);

R = corr2(I,J)

it showing error like

Error using medfilt2

Expected input number 1, A, to be two-dimensional.

Error in medfilt2>parse_inputs (line 107)

validateattributes(a, ...

Error in medfilt2 (line 49)

[a, mn, padopt] = parse_inputs(args{:});

Error in untitled15 (line 6)

J = medfilt2(I);

>>

Answer 1

[Tala]

I needs to be grayscale image. you want to convert your image to grayscale before passing ut to your filter. use imgtype = getImageType(I) and then convert it to grayscale

Answer 2

[nune pratyusha]

but i am getting different hystogram plots using below code

A = imread('Figure11(b).png');

Ref = imread('Figure(b).png');

montage({A,Ref})

figure

displayHistogramChannels(A,Ref)

my output is comes like in untitled.fig

how to get histogram plots like Untitled.png