doubt in the specific lines

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 (,:,:,).

Answer 1

[Deepak Gupta]

':' 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.

[Rd]

i understood. thank you so much for your explanation