i am getting this error

i=imread("Lena512.png")
i_i=im2double(i);
k=ones(4,4)/16;
b=1
conv2d(i_i,k,512)

function conv2d(i,k,b)
    [m,n]= size(k);
    [y,x]=size(i);
     y=y-m+1;
     x=x-m+1;
     ni=zeros(y,x)
       for l=2:1:y
           for j=2:1:x
                ni(l,j)=sum(i(l:l+m-1,j:j+n-1)*k)+b
           end
       end
end

Unable to perform assignment because the size of the left side is 1-by-1 and the size of the right side is 1-by-4.

Error in untitled2>conv2d (line 15)

ni(l,j)=sum(i(l:l+m-1,j:j+n-1)*k)+b

respective python code its working

# -*- coding: utf-8 -*-
"""
Created on Mon Oct 24 21:29:27 2022

@author: rishi
"""

import numpy as np
import cv2
import os
os.chdir(r"C:\Users\rishi\Downloads")
image=cv2.imread("Lena512.png")
image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
k=np.ones([4,4],dtype='int')/16
def convolution2d(image, kernel,bias):
    m, n = kernel.shape
    if (m == n):
        y, x = image.shape
        y = y - m + 1
        x = x - m + 1
        new_image = np.zeros((y,x))
        for i in range(y):
            for j in range(x):
                new_image[i][j] = np.sum(image[i:i+m, j:j+m]*kernel) + bias
    return new_image
x=convolution2d(image,k,bias=1)
cv2.imwrite('blurrey.jpg',x)

Answer 1

[DGM]

Two things:

• use elementwise multiplication between the sample and the filter kernel
• sum() normally only takes the sum over the first non-singleton dimension. If you need the sum over more than one dimension, you'll have to do so in one way or another.

This is a start

inpict = imread('cameraman.tif');
inpict = im2double(inpict);

fk = ones(4,4)/16; % sum-normalized 
b = 0; % offset?

outpict = conv2d(inpict,fk,b);
imshow(outpict)

function output = conv2d(thisimg,thisfk,offset)
    [m,n] = size(thisfk);
    [y,x] = size(thisimg);
    
    y = y-m+1;
    x = x-m+1;
    output = zeros(y,x);
    
    for l = 2:1:y
        for j = 2:1:x
            sample = thisimg(l:l+m-1,j:j+n-1);
            output(l,j) = sum(sample.*thisfk,'all') + offset;
        end
    end
end

Depending on your goals, the window positioning and image padding may be issues of concern. See the related questions and answers.

general sliding/moving window filter base

https://www.mathworks.com/matlabcentral/answers/1466576-changing-a-3x3-to-5x5-median-filter

same thing only with a gaussian mean setup

https://www.mathworks.com/matlabcentral/answers/1648495-i-am-trying-to-write-a-program-for-a-grayscale-image-blurring-without-using-gaussian-or-conv2-functi

basic mean filter examples

https://www.mathworks.com/matlabcentral/answers/1571763-rgb2gray-by-5-5-vicinity-marix

https://www.mathworks.com/matlabcentral/answers/1632145-mean-filter-with-kernel-size

basic convolution build (full size)

https://www.mathworks.com/matlabcentral/answers/820635-how-to-convolve-two-matrices-with-different-sizes

basic convolution build (same size)

https://www.mathworks.com/matlabcentral/answers/791809-2d-convolution-with-same-dimensions