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Applying Matlab Images Filter On RGB Images

i have the following Matlab code to manipulate two images, gray scale image, and RGB image. The point is to apply Average,Gaussian, and Laplacian filters on both images.

%%Clear
clear
clc
%%Reading images
gray=imread('cameraman.tif')
[gray_table gray_map]=gray2ind(gray,256)
rgb=imread('peppers.png')
[rgb_table rgb_map]=rgb2ind(rgb,256)
%%Creating filters
average=fspecial('average',3)
gaussian=fspecial('gaussian',3,0.5)
laplacian=fspecial('laplacian',0.9)
%%Applying filters
average_filterd_gray_table=imfilter(gray_table,average)
gaussian_filterd_gray_table=imfilter(gray_table,gaussian)
laplacian_filterd_gray_table=imfilter(gray_table,laplacian)
average_filterd_rgb_table=imfilter(rgb_table,average)
gaussian_filterd_rgb_table=imfilter(rgb_table,gaussian)
laplacian_filterd_rgb_table=imfilter(rgb_table,laplacian)
%%view
figure
subplot(1,4,1),imshow(gray_table,gray_map),title('Original Indexed Gray')
subplot(1,4,2),imshow(average_filterd_gray_table,gray_map),title('Average Filtered Indexed Gray')
subplot(1,4,3),imshow(gaussian_filterd_gray_table,gray_map),title('Gaussian Filtered Indexed Gray')
subplot(1,4,4),imshow(laplacian_filterd_gray_table,gray_map),title('Laplacian Filtered Indexed Gray')
figure
subplot(1,4,1),imshow(rgb_table,rgb_map),title('Original Indexed RGB')
subplot(1,4,2),imshow(average_filterd_rgb_table,rgb_map),title('Average Filtered Indexed RGB')
subplot(1,4,3),imshow(gaussian_filterd_rgb_table,rgb_map),title('Gaussian Filtered Indexed RGB')
subplot(1,4,4),imshow(laplacian_filterd_rgb_table,rgb_map),title('Laplacian Filtered Indexed RGB')

The code is working fine for the gray scale image. but on RGB image it just gives a distorted result. How to fix that?

Solution

  • According to the doc for rgb2ind (click here):

    when loading a rgb image like so:

    [X,map] = rgb2ind(RGB,n), the doc says:

    Note The values in the resultant image X are indexes into the colormap map and should not be used in mathematical processing, such as filtering operations.

    So you might be better off filtering directly the RGB images. The following works fine:

    clear
clc
close all

RGBImage = imread('peppers.png');

average = fspecial('average',3);
gaussian=fspecial('gaussian',3,0.5);
laplacian=fspecial('laplacian',0.9);

RGB_Average = imfilter(RGBImage,average);
RGB_Gaussian= imfilter(RGBImage,gaussian);
RGB_Laplacian = imfilter(RGBImage,laplacian);

figure;
subplot(2,2,1)
imshow(RGBImage)
title('Original')

subplot(2,2,2)
imshow(RGB_Average)
title('Average')

subplot(2,2,3)
imshow(RGB_Gaussian)
title('Gaussian')

subplot(2,2,4)
imshow(RGB_Laplacian)
title('Laplacian')

    which gives this:

    enter image description here