How do i save pic to the same png rather than creating a new png each time a pic is taken

Question

i have a question, How do i save pic to the same png rather than creating a new png each time a pic is taken

this is the command that execute the pic:

*cd ~
mkdir picture
cd picture
screen
raspistill -o a%04d.jpg -t 21600000 -tl 30000*

taken from this website: http://computers.tutsplus.com/tutorials/creating-time-lapse-photography-with-a-raspberry-pi--cms-20794

Answer 1

The command you want to change is raspistill -o a%04d.jpg -t 21600000 -tl 30000*

The filename portion of that follows the -o switch: a%04d.jpg I'm not sure whats being replaced without further study but the % is allowing the expanded file name to change with each run.

Change that to a plain file name such as photo.jpg.

Resulting in raspistill -o photo.jpg -t 21600000 -tl 30000*

Now each new photo will replace the last.

Note: your title reflects .png the command however clearly has .jpg for file type.