How to obtain the array of black pixel columnwise??

here I want to get the size of the letter.For that i want the array of black pixels columnwise.I know to calculate the entire pixels of the word.But please help me with this.

Answer 1

[Walter Roberson]

col_idx_first_black = sum(cumprod(YourImage,1)) + 1;
col_idx_last_black  = size(YourImage,1) - sum(cumprod(flipud(YourImage),1));
col_letter_size = max(0, col_idx_last_black - col_idx_first_black + 1);

Note: col_letter_size will be 0 for columns that contain no black. The first occupied row for the column will be in col_idx_first_black and the last occupied row for the column will be in col_idx_last_black (but those will have misleading values if the row has no black.)

[Poornima Gokhale]

Sir, its not working.I am getting the following error. Error using cumprod CUMPROD is only supported for floating point input.

Error in col (line 2) col_idx_first_black = sum(cumprod(YourImage,1)) + 1;

[Walter Roberson]

dImage = double(YourImage);
col_idx_first_black = sum(cumprod(dImage,1)) + 1;
col_idx_last_black  = size(dImage,1) - sum(cumprod(flipud(dImage),1));
col_letter_size = max(0, col_idx_last_black - col_idx_first_black + 1);

[Walter Roberson]

When I test in R2014a, I do not get that error: cumprod works on logical values and uint8 and int64 and uint64, and for char or struct values you get the typical

Undefined function 'cumprod' for input arguments of type 'char'.

Which MATLAB version are you using?

[Poornima Gokhale]

I am using 2012a. And i did not understand your note.

[Poornima Gokhale]

And i am getting 0 for col_letter_size for every column

[Poornima Gokhale]

Sir. now its working. I am getting 182 columns and its values. Does it mean that it is considering the first column and visiting all the rows of that column and giving its black pixel. If so how many rows are there?

[Walter Roberson]

It is visiting every column and locating the first black pixel in the column and returning the row index within the column. It also visits every column and locates the last black pixel in the column and returns the row index within the column. It also calculates the difference between the first and last index for each column in order to tell you the "size" in rows of the letter in that column -- but keep in mind that two columns that are the same "size" for the letter might have very different locations within the column.

The total number of rows in the image is size(YourImage,1)

[Poornima Gokhale]

thanks a lot sir.