lighthouse.jpg imread into matrix and calculate mean and std? - Homework

28 次查看（过去 30 天）
Nora
Nora 2013-11-19
评论： DGM 2024-11-18，5:10
Attached it the lighthouse.jpg. I am trying to use imread to load this picture onto a matrix. Then I am trying to calculate and print the mean separately of the red, green, and blue components in the matrix and also the standard deviation for each. I am having trouble getting the mean and std to work.
This is my script.
im1 = imread('Lighthouse.jpg'); % READ IMAGE
imshow(im1); % SHOW IMAGE
size(im1); % SIZE BY [ROW COLUM COLORMATRIX]
% COLORMATRIX USUALLY 3 WHICH IS FOR
% RGB, AND SHOWS 3 MATRIXES OF
% [ROW COLUM] DIMENTIONS.
imr = im1(:,:,1); % SHOW TRUE COLOR IMAGING FOR RGB IN SUBPLOTS
img = im1(:,:,2);
imb = im1(:,:,3);
immr = mean(mean(imr));
immg = mean(mean(img));
immb = mean(mean(imb));
imsr = std(std(imr));
imsg = std(std(img));
imsb = std(std(imb));
subplot(3,3,1);
imshow(im1);
subplot(3,3,2);
imshow(immr);
subplot(3,3,3);
imshow(immg);
subplot(3,3,4);
imshow(immb);
subplot(3,3,5);
What happens to be the problem?

请先登录，再回答此问题。

采纳的回答

Image Analyst
Image Analyst 2013-11-19
编辑：Image Analyst 2024-11-16，22:54
Ran in:
The standard deviation of the standard deviation of the columns is not the standard deviation of the entire image! It's not like the max, min, and mean functions. Try a simple example and you'll see. Just do
%imsr = std(imr(:));
to get the standard deviation of an entire array (a single color channel). imr(:) converts the 2D array into a 1D array.
% Demo by Image Analyst.
% Initialization steps.
clc; % Clear the command window.
fprintf('Beginning to run %s.m ...\n', mfilename);
Beginning to run LiveEditorEvaluationHelperEeditorId.m ...
close all; % Close all figures (except those of imtool.)
clearvars;
workspace; % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 16;
% Read in original image.
rgbImage = imread('lighthouse.png'); % READ IMAGE
[rows, columns, numberOfColorChannels] = size(rgbImage) % SIZE IS [ROWS COLUMNS NUMCOLORs]
rows = 640
columns = 480
numberOfColorChannels = 3
[redChannel, greenChannel, blueChannel] = imsplit(rgbImage);
meanRedValue = mean(redChannel, 'all');
meanGreenValue = mean(greenChannel, 'all');
meanBlueValue = mean(blueChannel, 'all');
sdRed = std(double(redChannel(:)));
sdGreen = std(double(greenChannel(:)));
sdBlue = std(double(blueChannel(:)));
subplot(2, 2, 1);
imshow(rgbImage);
title('Original Image');
subplot(2, 2, 2);
imshow(redChannel);
caption = sprintf('Red Channel.\nMean = %.2f, SD = %.2f', meanRedValue, sdRed);
title(caption);
subplot(2, 2,3);
imshow(greenChannel);
caption = sprintf('Green Channel.\nMean = %.2f, SD = %.2f', meanGreenValue, sdGreen);
title(caption);
subplot(2, 2,4);
imshow(blueChannel);
caption = sprintf('Blue Channel.\nMean = %.2f, SD = %.2f', meanBlueValue, sdBlue);
title(caption);
  6 个评论
显示 4更早的评论
DGM
DGM 2024-11-17，0:28
编辑：DGM 2024-11-17，0:31
Ran in:
inpict = imread('lighthouse.png');
inpict = reshape(inpict,[],size(inpict,3));
channelwisemean = mean(inpict,1)
channelwisemean = 1×3
106.4334 150.0902 171.3984
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
channelwisestd = std(double(inpict),0,1)
channelwisestd = 1×3
70.6482 66.4553 87.9043
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>

请先登录，再进行评论。

更多回答（2 个）

Walter Roberson
Walter Roberson 2013-11-19
The mean and standard deviations are scalar values; you would not show a scalar value as an image. You might fprintf() the values out on a single line (or two) though.
Dimitrios
Dimitrios 2024-11-16，19:21
can you help me with ghow to get the code for the lighthouse pic and also l,a,b code and pic?
  5 个评论
显示 3更早的评论
Image Analyst
Image Analyst 2024-11-17，15:20
Ran in:
@Dimitrios, @DGM pretty much already gave you the code. If you'd like a more fleshed out demo, then try this:
% Demo by Image Analyst.
% Initialization steps.
clc; % Clear the command window.
fprintf('Beginning to run %s.m ...\n', mfilename);
Beginning to run LiveEditorEvaluationHelperEeditorId.m ...
close all; % Close all figures (except those of imtool.)
clearvars;
workspace; % Make sure the workspace panel is showing.
format long g;
format compact;
% Read in original image.
rgbImage = imread('lighthouse.png'); % READ IMAGE
[rows, columns, numberOfColorChannels] = size(rgbImage) % SIZE IS [ROWS COLUMNS NUMCOLORs]
rows = 640
columns = 480
numberOfColorChannels = 3
[redChannel, greenChannel, blueChannel] = imsplit(rgbImage);
meanRedValue = mean(redChannel, 'all');
meanGreenValue = mean(mean(greenChannel));
meanBlueValue = mean(mean(blueChannel));
sdRed = std(double(redChannel(:)));
sdGreen = std(double(greenChannel(:)));
sdBlue = std(double(blueChannel(:)));
subplot(2, 2, 1);
imshow(rgbImage);
title('Original Image');
subplot(2, 2, 2);
imshow(redChannel);
impixelinfo; % Let user mouse around and see values displayed on the figure.
caption = sprintf('Red Channel.\nMean = %.2f, SD = %.2f', meanRedValue, sdRed);
title(caption);
subplot(2, 2, 3);
imshow(greenChannel);
impixelinfo; % Let user mouse around and see values displayed on the figure.
caption = sprintf('Green Channel.\nMean = %.2f, SD = %.2f', meanGreenValue, sdGreen);
title(caption);
subplot(2, 2, 4);
imshow(blueChannel);
impixelinfo; % Let user mouse around and see values displayed on the figure.
caption = sprintf('Blue Channel.\nMean = %.2f, SD = %.2f', meanBlueValue, sdBlue);
title(caption);
% Convert RGB image into LAB image.
labImage = rgb2lab(rgbImage);
[lImage, aImage, bImage] = imsplit(labImage);
% Display them
figure; % Open up a new window.
subplot(2, 2, 1);
imshow(rgbImage);
title('Original Image');
subplot(2, 2, 2);
imshow(lImage, []);
impixelinfo; % Let user mouse around and see values displayed on the figure.
title('L Image');
subplot(2, 2, 3);
imshow(aImage, []);
impixelinfo; % Let user mouse around and see values displayed on the figure.
title('A Image');
subplot(2, 2, 4);
imshow(bImage, []);
impixelinfo; % Let user mouse around and see values displayed on the figure.
title('B Image');
To learn other fundamental concepts, invest 2 hours of your time here:
MATLAB Academy - Free 2 hour training
DGM
DGM 2024-11-18，5:10
@Dimitrios Repeating it doesn't clarify anything. You haven't answered any of the questions I've asked you, so there's nothing new to tell you other than the same guesses. If that's not what you want, you have to explain why.
To repeat:
There are multiple standard images of lighthouses. Which one? Does it matter? If it doesn't matter, why does it even need to be a lighthouse?
If you're asking for "the l, a and b", I have to assume you're talking about CIELAB. If you are, then we've both given you examples. That much might seem obvious, but arguably the most common standard "lighthouse picture" is grayscale, so it's plausible that the request for the LAB image doesn't make sense in context.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Image Quality 的更多信息

标签

产品

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by