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doubt in the specific lines

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Rd
Rd on 23 Jul 2020
Commented: Rd on 23 Jul 2020
could you explain this line
mask_h=4;
mask_w=20
mask = zeros(mask_h,mask_w);
mask(1:mask_h/2,:) = -1;
mask(mask_h/2 + 1:end,:) = 1;
img_filt = imfilter(img, mask,'replicate');
img_filt_up = img_filt(1:floor(img_h/2),:);
i cant understand what it means in general (,:,:,).

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Accepted Answer

Deepak Gupta
Deepak Gupta on 23 Jul 2020
':' means 'All'.
For example in your code you have created a mask of size 4*20 and initialized it with zeros. i.e.
mask = zeros(mask_h,mask_w);
In the next line you are assigning some perticular values to your mask. i.e.
mask(1:mask_h/2,:) = -1;
Here, 1: mask_h/2 = 1:2, because mask_h has value 4
and then ':' means 'All'. First index represents rows and second one column. So this line of code will assign value -1 to rows from 1 to 2 and in all columns. You can verify it by printing the mask value.
Same is for next line, where value of 1 is assigned for rest of the rows (3 to 4) in all columns.
If you don't want to assign values in all columns, then you will write something like:
mask(1:2, 1:10) = -1. Here value -1 will be assigned for rows 1 to 2 and columns 1 to 10 only.

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Rd
Rd on 23 Jul 2020
i understood. thank you so much for your explanation

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