upload exercises

Exercise2c/README.md

@@ -0,0 +1,20 @@
+## Exercise 2c
+
+Processing images with simultaneous multiprocessing and multithreading.
+
+`process_image.py` processes a single image.
+It can be used as a script: `process_image.py foo.jpg`
+It is also an importable module. `process_image.magic("foo.jpg")`
+
+`process_multiple_images` uses `process_image` to process a series of images.
+It should be called as following:
+`process_multiple_images n_processes n_threads filename1.png filename2.png …`
+
+1. start a separate terminal window with `htop`: `gnome-terminal -- htop &`
+
+2. call `python process_multiple_images.py 2 2 images/*.png`
+
+You should see `htop` showing 4 threads (2 worked processes × 2 numpy threads).
+
+Play with different numbers of processes and threads.
+Which combination is optimum (fastest)?