To my understanding, you have created a noise reduction code but cannot see the output image.
The error is probably coming in line 8 of your code i.e.
k = filter2(fspecial('average',3),g)/255;
It is because this filter is in return using conv2 on RGB image which is not supported. Hence, you need to convert the RGB image to gray then perform the operations.
The code would look like:
f = imread("peppers.png");
f = rgb2gray(f); %% converting to grayscale
imshow(f),title('original image');
g =imnoise(f,'gaussian',0,0.1);
figure,imshow(g),title('noisy image')
h = fspecial('unsharp');
j =imfilter(g,h);
figure,imshow(j),title(' linear filtered image')
k = filter2(fspecial('average',3),g)/255;
figure,imshow(k),title('FIR filtered image')
l = medfilt2(g,[3 3]);
figure,imshow(l),title(' median filtered image')
m = wiener2(g,[5 5]);
figure, imshow(m),title('adaptive filtered image')
You can refer to rgb2gray MathWorks Documentation page to learn more on converting RGB image or colormap to grayscale.
