Undefined function 'conv2' for input arguments of type 'double' and attributes 'full 3d real'. - Matlab

Question

I'm trying to filter an image in the space domain so i'm using the conv2 function.

here's my code.

cd /home/samuelpedro/Desktop/APIProject/

close all
clear all
clc

img = imread('coimbra_aerea.jpg');
%figure, imshow(img);

size_img = size(img);

gauss = fspecial('gaussian', [size_img(1) size_img(2)], 50);

%figure, surf(gauss), shading interp

img_double = im2double(img);

filter_g = conv2(gauss,img_double);

I got the error:

Undefined function 'conv2' for input arguments of type 'double' and attributes 'full 3d
real'.

Error in test (line 18)
filter_g = conv2(gauss,img_double);

now i'm wondering, can't I use a 3 channel image, meaning color image.

Answer 1

Color images are 3 dimensional arrays (x,y,color). conv2 is only defined for 2-dimensions, so it won't work directly on a 3-dimensional array.

Three options:

• Use an n-dimensional convolution, convn()

• Convert to a grayscale image using rgb2gray(), and filter in 2D:

  filter_g = conv2(gauss,rgb2gray(img_double));

• Filter each color (RGB) separately in 2D:

  filter_g = zeros(size(im_double));
  for i = 1:3
    filter_g(:,:,i) = conv2(gauss, im_double(:,:,i);
  end