A ’BGR’ image.

a 3x3 Gaussian filter with BGR image Thanks.

Answer 1

[Constantino Carlos Reyes-Aldasoro]

Hello:

First, changing channels is very simple you just need to change the third dimension of the image, e.g.

image1=imread('peppers.png');
imagesc(image1)

Now, let's change channels from RGB to BGR:

image2(:,:,1) = image1(:,:,3);
image2(:,:,2) = image1(:,:,2);
image2(:,:,3) = image1(:,:,1);
imagesc(image2)

Now in terms of the filtering with a Gaussian, if you apply a 3x3 to every channel, that would be the same if you do in RGB or in BGR as you are averaging pixels in a channel.

Hope that answers your question.

[Ben Ma]

Can you also apply a 3x3 Gaussian filter to the original RGB image please? thanks

[Constantino Carlos Reyes-Aldasoro]

Yes, you can apply the filter to the original or to the transformed. E.g. to apply to the RGB you do the following:

image1=imread('peppers.png');
image1_filtered = imfilter(image1,  fspecial('Gaussian',3,1));
figure
subplot(221)
imagesc(image1)
subplot(222)
imagesc(image1_filtered)
subplot(223)
imagesc(image1(100:150,100:150,:))
subplot(224)
imagesc(image1_filtered(100:150,100:150,:))

If you want to apply to the transformed, do the same once it has been transformed.

Answer 2

[Image Analyst]

Ben, you can use imgaussfilt(). It's very straightforward but let us know if you can't figure out my code below.

clc;    % Clear the command window.
clear all;
close all;
workspace;  % Make sure the workspace panel is showing.
format short g;
format compact;
fontSize = 15;
fprintf('Beginning to run %s.m ...\n', mfilename);

rgbImage = imread('peppers.png');
subplot(2, 1, 1);
imshow(rgbImage);
title('Original Image', 'FontSize', fontSize);
% Split into channels.
[r, g, b] = imsplit(rgbImage);
% Blur each channel.
sigma = 9; % Whatever.
smoothr = imgaussfilt(r, sigma);
smoothg = imgaussfilt(g, sigma);
smoothb = imgaussfilt(b, sigma);
% Combine individual blurred color channels into a new RGB image.
blurredImage = cat(3, smoothr, smoothg, smoothb);
% Display the blurred image.
subplot(2, 1, 2);
imshow(blurredImage);
caption = sprintf('Blurred with a sigma of %.1f', sigma);
title(caption, 'FontSize', fontSize);