Hi Ozan, the below code might help!
img = imread('kodim07.png');
imshow(img)
img = imresize(img, 2, 'bicubic');
figure
imshow(img)
% define filter kernel
kernel = [1, -5, 20, 20, -5, 1] / 32;
% extracting rgb channels individually
rChannel = img(:, :, 1);
gChannel = img(:, :, 2);
bChannel = img(:, :, 3);
% applying filter to the extracted matrices separately
rChannelNew = filter2(kernel, rChannel);
gChannelNew = filter2(kernel, gChannel);
bChannelNew = filter2(kernel, bChannel);
% concatenate matrices along 3rd dimension
outputImg = cat(3, rChannelNew, gChannelNew, bChannelNew);
% convert the numeric matrix to image
outputImg = mat2gray(outputImg);
figure
imshow(outputImg)