Error in computing median filter and histogram equalization on an image. How can i solve it?

I am trying to perform median filter on an image using simple median filter code like this

a = imread('1a.jpg');
figure; imshow (a)
b = imnoise(a,'salt & pepper',0.02);
figure; imshow (b)
c = medfilt2(b);
figure; imshow (c)

but i am getting this error:

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 48)

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

Error in medianFilter (line 11)

c = medfilt2(b);

Also when i tried to perform histogram equalization also using this code

a = imread('1a.jpg');
img_eq = histeq(a); 
figure; imshow(img_eq);

I also get this error:

Error using histeq

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

Error in histeq (line 69)

validateattributes(a,{'uint8','uint16','double','int16','single'}, ...

Error in Histogramequalization (line 13)

img_eq = histeq(a);

How can i go about it pls.

Here are the two types of images i used.

Answer 1

[DGM]

The image is a JPG, and most JPGs are RGB.

fname = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/280425/1a.jpg';
inpict = imread(fname); % RGB, uint8
size(inpict) % this is not a single-channel image

ans = 1×3

181 146 3

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We can also look at metadata if that's not certain enough

S = imfinfo(fname);
S.ColorType % 24b RGB

ans = 'truecolor'

S.NumberOfSamples % 3 channels

ans = 3

S.BitDepth % 8b x 3channels = 24b

ans = 24

If the image is nominally gray and is to be treated as gray, then just convert it using im2gray() (or rgb2gray() in older versions)

% the simple modern way
% im2gray() will convert RGB inputs and pass gray inputs
graypict1 = im2gray(inpict);

% but rgb2gray() will throw an error if it receives anything but a 3-ch image,
% so you have to do its input handling for it externally.
% if you're not going to use anything older than R2020b, just use im2gray().
if size(inpict,3) ~= 1
    graypict2 = rgb2gray(inpict);
end

See also:

https://www.mathworks.com/matlabcentral/answers/261817-how-to-remove-error-error-using-iptcheckinput-function-medfilt2-expected-its-first-input-a#answer_1555551