How do I understand the following code?

Hello,

I found this code online and I am trying to understand it for my study. I am unable to understand the following lines of code and I was wondering if someone will assist me in understanding. Specifically, I don't understand the part "%set the image size to suitable value" where it is giving scale and resizing the image and "%% image Resize"

%% Uploading input image
[filename,pathname] = uigetfile('*.*','Choose the input image');
im = imread([pathname,filename]);
% set the image size to suitable value
scale = 600/(max(size(im(:,:,1))));        
im = imresize(im,scale*size(im(:,:,1)));
% % Image resize
[m,n,~] = size(im);

I would appreciate the assistance.

Thank you in advance.

Answer 1

[Adam Danz]

The best way to understand it is by using the help or doc commands to look up each function name. At the top of each page you'll see a brief description of the function, inputs and outputs.

Here's a very general description of each line

% CHOOSE A FILE
[filename,pathname] = uigetfile('*.*','Choose the input image');

% READ THE IMAGE FILE IN AS IMAGE DATA
im = imread([pathname,filename]);

% DETERMINE THE SCALE OF THE IMAGE DATA 
% (max(size(...)) returns the images maximum dimension 
% THE IMAGE DATA (im) IS AN nXmX3 ARRAY OF R-G-B- COLOR VALUES
% BUT THIS LINE ONLY REFERENCES THE "R" VALUES
scale = 600/(max(size(im(:,:,1))));       

% SCALE THE IMAGE
im = imresize(im,scale*size(im(:,:,1)));

% GET THE NEW IMAGE SIZE
[m,n,~] = size(im);

You can use imshow(im) to see the image.

[Vinay Chawla]

Thank you. I tried using the help or doc commands for functions and got some of them but not the othres.

The line " scale = 600/(max(size(im(:,:,1)))); " is still very unclear to me.

What is it doing?

Is it creating a scale for the image? or setting it to the actual scale of the image.

as for the " im = imresize(im,scale*size(im(:,:,1)));" Is this resizing the image based on actual scale (Ground Distance).

These lines are part of the code for determining crack dimensions. So I was wondering if the scale and resizing is given based on the actual field dimensions.

I am very new to MATLAB and Image Processing and I would really appreciate if you can provide an easier and detailed explanation on this.

Thank you for your help.

[Adam Danz]

"Is it creating a scale for the image?"

Yes.

This section gets the size of the first two dimensions of the image (width & height)

 size(im(:,:,1))

This returns the max (width or height)

(max(size(im(:,:,1)))

This computes the scaling factor. So, if you're working with a tall image (height>width), then this will divide 600 by the height of the image. If height is smaller than 600, the scaling factor will be larger than 1 so the size of the image will increase. I don't know where 600 comes from.

600/(max(size(im(:,:,1))))

[Image Analyst]

It's possible that they want the algorithm to work for any size image but some of the parameters, for example filter window sizes, are built assuming a certain size of the image in pixels. If the image is not that size (say they're 10 times bigger), then the filters might not work as intended - as they did for the smaller images.

[Vinay Chawla]

Thank you so much for your responses. I really appreciate.

About the line "((max(size(im(:,:,1)))", only referencing the R-Values. After analyzing the image, I realized all the three color channerl values are similar. It is possible that that is the reason why only R value is considered? And is it possible that an image will have all the same RGB values? Please refer to th image below:

II would really appreciate any assistance in this regard.

Thank you.

[Adam Danz]

> It is possible that that is the reason why only R value is considered?

Possibly. I advise reading about the array returned by imread so you can you can understand what im is

https://www.mathworks.com/help/matlab/ref/imread.html#btnczv9-1-A

> is it possible that an image will have all the same RGB values

Yes, when all 3 RGB values are the same, it's a shade of gray/black.white

rgb = repmat(0:.1:1, 3,1)'

rgb = 11×3

0 0 0 0.1000 0.1000 0.1000 0.2000 0.2000 0.2000 0.3000 0.3000 0.3000 0.4000 0.4000 0.4000 0.5000 0.5000 0.5000 0.6000 0.6000 0.6000 0.7000 0.7000 0.7000 0.8000 0.8000 0.8000 0.9000 0.9000 0.9000

●

scatter(1:11,.5.*ones(1,11),250,rgb,'filled','MarkerEdgeColor','k')

●

[Vinay Chawla]

Thank you.