wrote more explanations

docs/exercise3.rst

@@ -3,8 +3,8 @@ Exercise 3: Manage data in files and command line input
 
 The purpose of this exercise is to learn how to pass data between fireworks as 
 files and process these data using the custom ``CommandLineTask``. The built-in 
-``ScriptTask`` used in **Exercise 1** allows to run a script which does not provide 
-methods to stage data between fireworks and handling of command line options, flags 
+``ScriptTask`` used in **Exercise 1** allows to run a script but provides no
+methods to move data between fireworks and no handling of command line options, flags 
 input and output as workflow data. 
 
 Given is a set of reusable operations implemented using the ``convert`` and 
@@ -18,7 +18,7 @@ command line flags. These are:
     - Swirl
     - Animate
 
-The corresponding fireworks with test inputs can be found in 
+The fireworks corresponding to these operations can be found in 
 **exercises/demos/3_files_and_commands**. The provided solutions in 
 **exercises/solutions/3_files_and_commands** are suitable for the input for 
 letter "A" in **exercises/inputs/3_files_and_commands/A**. 
@@ -26,25 +26,28 @@ letter "A" in **exercises/inputs/3_files_and_commands/A**.
 Problem 3.1
 -----------
 
-The input files are images of different 2x2-tiled capital letters. Some of the 
-input tiles are rotated or mirrored vertically or horizontally and some missing 
+The input image files are some parts of 2 × 2 tiled capital letters. Some of 
+the input tiles are rotated or mirrored vertically or horizontally and some missing 
 tiles can be recovered by the same operations using the symmetry. The task is 
 to recover all tiles and put them together to reconstruct the image of the 
 selected letter.
 
-Select input images for a letter from the folder **exercises/inputs/3_files_and_commands**. 
-Then use the provided fireworks and compose a workflow for the selected letter 
-by adjusting the concrete parameters, inputs and outputs. Verify, add and run the 
-workflow and check the resulting image.
+Select a set of input images (**piece-1.png** and **piece-2.png**) for a letter 
+from the folder **exercises/inputs/3_files_and_commands**. 
+Then use the provided fireworks and compose a workflow to reconstruct the 
+selected letter by adjusting the image processing parameters, inputs and outputs. 
+Verify, add and run the workflow and check the resulting image.
 
 
 Problem 3.2
 -----------
 
-Given an image as input, swirl the image at the angles 90°, 180°, 270° and 360°
+Given an image as input, "swirl" the image at the angles 90°, 180°, 270° and 360°
 producing four new images. Arrange the original and the resulting images in the 
 sequence: 
 
 0° → 90° → 180° → 270° → 360° → 270° → 180° → 90° → 0°
 
-and make an animation.
+and make an animation. As input you can use either the image file **letter.png**
+from **exercises/inputs/3_files_and_commands** or the reconstructed image from
+**Problem 3.1**.