The purpose of code on programming

Hi.

I met a few questions when i watch this code

i seen the comment, but i have no idea why the picture produced like that.

i also confuse for the imageData=[imageData; imageRow]; i know the function of ";", but why it used in here?

% make a 2d array of values.

imageData=[]; % set up an empty array

imSize=100;

numRows=imSize;

numCols=imSize;

%populate using a nested loop

for row=[1:numRows]

imageRow=[]; %empty vector for row

for col=[1:numCols]

pixelVal=uint8((row+col)/(imSize*2) * 255); % make a pixel val in 0..255

imageRow=[imageRow pixelVal]; %add value for pixel

end

imageData=[imageData; imageRow]; % add row of pixels

end

% display as an image

imshow(imageData);

% save as an image

imwrite(imageData,'test.png');

% load an image

newImageData=imread('test.png');

% print information about what is stored in the variable

whos newImageData;

Answer 1

[Image Analyst]

I'm not sure why you said "i know the function of ";", but why it used in here?"

In

imageData=[imageData; imageRow];

the first semicolon says that the rowVector imageRow is to be concatenated below the 3-D matrix imageData.

They're essentially building up the matrix row-by-row by appending the current row to the matrix they're building up.

The second semicolon tells it not to type the whole matrix -- all values of it -- to the command window.

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[Shuoze Xu]

Ok, thank you.

And may you tell the purpose of pixelVal=uint8((row+col)/(imSize*2) * 255) on this program?

[Image Analyst]

That's the formula they're using to make the values go from 0 in the upper left to 255 in the lower right.

[Shuoze Xu]

I got it.

Thank you for your help.