Fundamentals of Python First Programs Chapter 7 Simple

Fundamentals of Python: First Programs Chapter 7: Simple Graphics and Image Processing Modifications by Mr. Dave Clausen

Objectives After completing this chapter, you will be able to: • Use the concepts of object-based programming— classes, objects, and methods—to solve a problem • Develop algorithms that use simple graphics operations to draw two-dimensional shapes • Use the RGB system to create colors in graphics applications and modify pixels in images Fundamentals of Python: First Programs 2

Objectives (continued) • Develop recursive algorithms to draw recursive shapes • Write a nested loop to process a two-dimensional grid • Develop algorithms to perform simple transformations of images, such as conversion of color to grayscale Fundamentals of Python: First Programs 3

Simple Graphics • Graphics: Discipline that underlies the representation and display of geometric shapes in two- and three-dimensional space • A Turtle graphics toolkit provides a simple and enjoyable way to draw pictures in a window – turtle is a non-standard, open-source Python module Fundamentals of Python: First Programs 4

Overview of Turtle Graphics • Turtle graphics originally developed as part of the children’s programming language Logo – Created by Seymour Papert and his colleagues at MIT in the late 1960 s • Analogy: Turtle crawling on a piece of paper, with a pen tied to its tail – Sheet of paper is a window on a display screen – Position specified with (x, y) coordinates • Cartesian coordinate system, with origin (0, 0) at the center of a window Turtle Graphics Documentation Fundamentals of Python: First Programs 5

Overview of Turtle Graphics (continued) • Together, these attributes make up a turtle’s state Fundamentals of Python: First Programs 6

Turtle Operations Fundamentals of Python: First Programs 7

Turtle Operations (continued) Fundamentals of Python: First Programs 8

Turtle Motion (Move and Draw) turtle. forward(distance) turtle. ftance) integer or float Move the turtle forward by the specified distance, in the direction the turtle is headed. turtle. back(distance) turtle. backward(distance) integer or float Move the turtle backward by distance, opposite to the direction the turtle is headed. Do not change the turtle’s heading turtle. right(angle) turtle. rt(angle) integer or float Turn turtle right by angle units. (Units are by default degrees, but can be set via the degrees() and radians() functions. ) Angle orientation depends on the turtle mode, turtle. left(angle) turtle. lt(angle) integer or float Turn turtle left by angle units. (Units are by default degrees, but can be set via the degrees() and radians() functions. ) Angle orientation depends on the turtle mode turtle. goto(x, y=None) turtle. setposition(x, y=None) x – a number or a pair/vector of numbers y – a number or None If y is None, x must be a pair of coordinates or a Vec 2 D (e. g. as returned by pos()). Move turtle to an absolute position. If the pen is down, draw line. Do not change the turtle’s orientation. Fundamentals of Python: First Programs 9

Turtle Motion (Move and Draw 2) turtle. setx(x) integer or float Set the turtle’s first coordinate to x, leave second coordinate unchanged. turtle. sety(y) integer or float Set the turtle’s second coordinate to y, leave first coordinate unchanged. turtle. setheading(to_angle) turtle. seth(to_angle) integer or float Set the orientation of the turtle to to_angle. Here are some common directions in degrees: standard mode logo mode 0 - east 0 - north 90 - north 90 - east 180 - west 180 - south 270 - south 270 – west turtle. home() turtle. circle(radius, extent=Non e, steps=None Move turtle to the origin – coordinates (0, 0) – and set its heading to its start-orientation (which depends on the mode, see mode()) radius – a number extent – a number (or None) steps – an integer (or None) Fundamentals of Python: First Programs Draw a circle with given radius. The center is radius units left of the turtle; extent – an angle – determines which part of the circle is drawn. If extent is not given, draw the entire circle. If extent is not a full circle, one endpoint of the arc is the current pen position. Draw the arc in counterclockwise direction if radius is positive, otherwise in clockwise direction. Finally the direction of the turtle is changed by the amount of extent. As the circle is approximated by an inscribed regular polygon, steps determines the number of steps to use. If not given, it will be calculated automatically. May be used to draw regular polygons. 10

Turtle Motion (Move and Draw 3) turtle. dot(size=Non e, *color) size – an integer >= 1 (if given) color – a colorstring or a numeric color tuple turtle. stamp() Draw a circular dot with diameter size, using color. If size is not given, the maximum of pensize+4 and 2*pensize is used. Stamp a copy of the turtle shape onto the canvas at the current turtle position. Return a stamp_id for that stamp, which can be used to delete it by calling clearstamp(stamp_id). turtle. clearstamp(sta mpid) stampid – an integer, must be return value of previous stamp() call Delete stamp with given stampid. turtle. clearstamps(n =None) n – an integer (or None) Delete all or first/last n of turtle’s stamps. If n is None, delete all stamps, if n > 0 delete first n stamps, else if n < 0 delete last n stamps turtle. undo() turtle. speed(speed= None) Undo (repeatedly) the last turtle action(s). Number of available undo actions is determined by the size of the undobuffer. . speed – an integer in the range 0. . 10 or a speedstring (see below) Fundamentals of Python: First Programs Set the turtle’s speed to an integer value in the range 0. . 10. If no argument is given, return current speed. If input is a number greater than 10 or smaller than 0. 5, speed is set to 0. Speedstrings are mapped to speedvalues as follows: “fastest”: 0 “fast”: 10 “normal”: 6 “slow”: 3 “slowest”: 1 Speeds from 1 to 10 enforce increasingly faster animation of line drawing and turtle turning. Attention: speed = 0 means that no animation takes place. forward/back makes turtle jump and likewise left/right make the turtle turn instantly. 11

Tell Turtle’s State turtle. position() turtle. pos() turtle. towards(x, y=None) Return the turtle’s current location (x, y) (as a Vec 2 D vector). x – a number or a pair/vector of numbers or a turtle instance y – a number if x is a number, else None Return the angle between the line from turtle position to position specified by (x, y), the vector or the other turtle. This depends on the turtle’s start orientation which depends on the mode - “standard”/”world” or “logo”). turtle. xcor() Return the turtle’s x coordinate. turtle. ycor() Return the turtle’s y coordinate. turtle. heading() Return the turtle’s current heading (value depends on the turtle mode, see mode()) turtle. distance(x, y=None ) x – a number or a pair/vector of numbers or a turtle instance y – a number if x is a number, else None Fundamentals of Python: First Programs Return the distance from the turtle to (x, y), the given vector, or the given other turtle, in turtle step units. . 12

Drawing State turtle. pendown() turtle. pd() turtle. down() Pull the pen down – drawing when moving. . turtle. penup() turtle. pu() turtle. up() Pull the pen up – no drawing when moving. turtle. pensize(width=None) turtle. width(width=None) width – a positive number turtle. isdown() turtle. pen(pen=None, **pen dict) Set the line thickness to width or return it. If resizemode is set to “auto” and turtleshape is a polygon, that polygon is drawn with the same line thickness. If no argument is given, the current pensize is returned. Return True if pen is down, False if it’s up. pen – a dictionary with some or all of the below listed keys pendict – one or more keywordarguments with the below listed keys as keywords Fundamentals of Python: First Programs Return or set the pen’s attributes in a “pen-dictionary” with the following key/value pairs: “shown”: True/False “pendown”: True/False “pencolor”: color-string or color-tuple “fillcolor”: color-string or color-tuple “pensize”: positive number “speed”: number in range 0. . 10 “resizemode”: “auto” or “user” or “noresize” “stretchfactor”: (positive number, positive number) “outline”: positive number “tilt”: number This dictionary can be used as argument for a subsequent call to pen() to restore the former pen-state. Moreover one or more of these attributes can be provided as keyword-arguments. This can be used to set several pen attributes in one statement. 13

Color Control turtle. pencolor(*args) Return or set Four input formats are allowed: the pencolor() Return the current pencolor as color specification string or as a tuple (see example). May be used as input to another color/pencolor/fillcolor call. pencolor(colorstring) Set pencolor to colorstring, which is a Tk color specification string, such as "red", "yellow", or "#33 cc 8 c". pencolor((r, g, b)) Set pencolor to the RGB color represented by the tuple of r, g, and b. Each of r, g, and b must be in the range 0. . colormode, where colormode is either 1. 0 or 255 (see colormode()). pencolor(r, g, b) Set pencolor to the RGB color represented by r, g, and b. Each of r, g, and b must be in the range 0. . colormode. turtle. fillcolor(*args) Return or set Four input formats are allowed: fillcolor() Return the current fillcolor as color specification string, possibly in tuple format (see the fillcolor. example). May be used as input to another color/pencolor/fillcolor call. fillcolor(colorstring) Set fillcolor to colorstring, which is a Tk color specification string, such as "red", "yellow", or "#33 cc 8 c". fillcolor((r, g, b)) Set fillcolor to the RGB color represented by the tuple of r, g, and b. Each of r, g, and b must be in the range 0. . colormode, where colormode is either 1. 0 or 255 (see colormode()). fillcolor(r, g, b) Set fillcolor to the RGB color represented by r, g, and b. Each of r, g, and b must be in the range 0. . colormode turtle. color(*args) Return or set pencolor and fillcolor. Several input formats are allowed. They use 0 to 3 arguments as follows: color() Return the current pencolor and the current fillcolor as a pair of color specification strings or tuples as returned by pencolor() andfillcolor(). color(colorstring), color((r, g, b)), color(r, g, b)Inputs as in pencolor(), set both, fillcolor and pencolor, to the given value. color(colorstring 1, colorstring 2), color((r 1, g 1, b 1), (r 2, g 2, b 2))Equivalent to pencolor(colorstring 1) and fillcolor(colorstring 2) and analogously if the other input format is used. Fundamentals of Python: First Programs 14

Filling Shapes turtle. filling() Return fillstate (True if filling, False else). turtle. begin_fill() To be called just before drawing a shape to be filled. turtle. end_fill() Fill the shape drawn after the last call to begin_fill(). Fundamentals of Python: First Programs 15

More Drawing Control turtle. reset() Delete the turtle’s drawings from the screen, recenter the turtle and set variables to the default values. turtle. clear() Delete the turtle’s drawings from the screen. Do not move turtle. State and position of the turtle as well as drawings of other turtles are not affected. turtle. write(arg, move=False, align="left", font=("Arial", 8, "normal")) arg – object to be written to the Turtle. Screen move – True/False align – one of the strings “left”, “center” or right” font – a triple (fontname, fontsize, fonttype) Fundamentals of Python: First Programs Write text - the string representation of arg - at the current turtle position according to align (“left”, “center” or right”) and with the given font. Ifmove is true, the pen is moved to the bottomright corner of the text. By default, move is False. 16

Turtle State - Visibility turtle. hideturtle() turtle. ht() Make the turtle invisible. It’s a good idea to do this while you’re in the middle of doing some complex drawing, because hiding the turtle speeds up the drawing observably. turtle. showturtle() turtle. st() Make the turtle visible. turtle. isvisible() Return True if the Turtle is shown, False if it’s hidden. Fundamentals of Python: First Programs 17

Window Control turtle. bgcolor(*args) args – a color string or three numbers in the range 0. . colormode or a 3 -tuple of such numbers Set or return background color of the Turtle. Screen turtle. clear() turtle. clearscreen() Delete all drawings and all turtles from the Turtle. Screen. Reset the now empty Turtle. Screen to its initial state: white background, no background image, no event bindings and tracing on. turtle. reset() turtle. resetscreen() Reset all Turtles on the Screen to their initial state. turtle. screensize(canvwidth=Non e, canvheight=None, bg=None) canvwidth – positive integer, new width of canvas in pixels canvheight – positive integer, new height of canvas in pixels bg – colorstring or colortuple, new background color Fundamentals of Python: First Programs If no arguments are given, return current (canvaswidth, canvasheight). Else resize the canvas the turtles are drawing on. Do not alter the drawing window. To observe hidden parts of the canvas, use the scrollbars. With this method, one can make visible those parts of a drawing which were outside the canvas before. 18

How to Configure Screen and Turtles If you want to use a different configuration which better reflects the features of this module or which better fits to your needs, , you can prepare a configuration file turtle. cfg which will be read at import time and modify the configuration according to its settings. The built in configuration would correspond to the following turtle. cfg: width = 0. 5 height = 0. 75 leftright = None topbottom = None canvwidth = 800 canvheight = 400 mode = standard colormode = 1. 0 delay = 10 undobuffersize = 1000 shape = classic pencolor = black fillcolor = black resizemode = noresize visible = True language = english exampleturtle = turtle examplescreen = screen title = Python Turtle Graphics using_IDLE = False Fundamentals of Python: First Programs 19

Turtle Operations (continued) • Interface: set of methods of a given class – Used to interact with an object – Use docstring mechanism to view an interface • help(<class name>) • help(<class name>. <method name>) draw. Square. py Fundamentals of Python: First Programs 20

Object Instantiation and the turtle Module • Before you apply any methods to an object, you must create the object (i. e. , an instance of) • Instantiation: Process of creating an object • Use a constructor to instantiate an object: • To instantiate the Turtle class: Fundamentals of Python: First Programs 21

Object Instantiation and the turtle Module (continued) • To close a turtle’s window, click its close box • Attempting to manipulate a turtle whose window has been closed raises an error Fundamentals of Python: First Programs 22

Object Instantiation and the turtle Module (continued) Fundamentals of Python: First Programs 23

Drawing Two-Dimensional Shapes • Many graphics applications use vector graphics, or the drawing of simple two-dimensional shapes, such as rectangles, triangles, and circles draw. Polygon. py Fundamentals of Python: First Programs 24

Drawing Two-Dimensional Shapes (continued) Fundamentals of Python: First Programs 25

Taking a Random Walk • Like any animal, a turtle can wander around randomly: random. Walk. py Fundamentals of Python: First Programs 26

Taking a Random Walk (continued) Fundamentals of Python: First Programs 27

Colors and the RGB System • Display area on a computer screen is made up of colored dots called picture elements or pixels • Each pixel represents a color – the default is black • RGB is a common system for representing colors – RGB stands for red, green, and blue – Each color component can range from 0 – 255 • 255 maximum saturation of a color component • 0 total absence of that color component – A true color system Fundamentals of Python: First Programs 28

Colors and the RGB System (cont’d) • Each color component requires 8 bits; total number of bits needed to represent a color value is 24 – Total number of RGB colors is 224 (16, 777, 216) Fundamentals of Python: First Programs 29

Example: Drawing with Random Colors • The Turtle class includes a pencolor method for changing the turtle’s drawing color – Expects integers for the three RGB components Fundamentals of Python: First Programs 30

Examining an Object's Attributes • Mutator methods change the internal state of a Turtle method – Example: pencolor method • Accessor methods return the values of a Turtle object’s attributes without altering its state – Example: position method Fundamentals of Python: First Programs 31

Manipulating a Turtle’s Screen • The Screen object’s attributes include its width and height in pixels and its background color • Use t. screen to access a turtle’s Screen object, then call a Screen method on this object Fundamentals of Python: From First Programs Through Data Structures 32

Background Scenes • After you have drawn your background scenes with turtle commands: – Press the “Print Screen” key on the keyboard to capture each background scene. – Edit and crop the picture in Paint or Photoshop to only include what you have drawn (keep this as 800 by 400 pixels, or as close to this as possible). – Save the pictures as GIF files using filenames like, Scene 1. gif, Scene 2. gif, etc. • Comment out all the function calls to functions that draw the backgrounds (Do NOT delete these functions. ) • Load the background scene using screen. bgpic("Background. Pic. gif") and the name of your background pictures. Fundamentals of Python: From First Programs Through Data Structures 33

Using Multiple Turtles • Instantiate more than one turtle, for example: t = Turtle() t 2 = Turtle() t 3 = Turtle() • Register and associate the turtles to shapes (. gif) t. screen. register_shape(“picture 1 name. gif") t 2. screen. register_shape(“picture 2 name. gif") t 3. screen. register_shape(“picture 3 name. gif") • Set the shape for each turtle t. shape(“picture 1 name. gif") t 2. shape(“picture 2 name. gif") t 3. shape(“picture 3 name. gif") • Use transparent GIF files for turtle shapes. Fundamentals of Python: From First Programs Through Data Structures 34

Simple Animation • You could have a loop moving each turtle with a delay to adjust the speed of the animation. Here is an example that moves three turtles a random number of pixels each iteration of the loop: for point in range(600): t. fd(random. randint(1, 3)) t 2. fd(random. randint(1, 3)) t 3. fd(random. randint(1, 4)) screen. delay(3) Fundamentals of Python: From First Programs Through Data Structures 35

Case Study: Recursive Patterns in Fractals • Fractals are highly repetitive or recursive patterns • A fractal object appears geometric, yet it cannot be described with ordinary Euclidean geometry • Strangely, a fractal curve is not one-dimensional, and a fractal surface is not two-dimensional – Every fractal shape has its own fractal dimension • One example of a fractal curve is the c-curve Fundamentals of Python: First Programs 36

Case Study: Recursive Patterns in Fractals (continued) Fundamentals of Python: First Programs 37

Case Study: Recursive Patterns in Fractals (continued) • Request: – Write a program that allows the user to draw a particular c-curve in varying degrees • Analysis: – Program should prompt the user for the level of the c -curve – Next, program should display a Turtle graphics window in which it draws the c-curve Fundamentals of Python: First Programs 38

Case Study: Recursive Patterns in Fractals (continued) • Design: Fundamentals of Python: First Programs 39

Case Study (continued) • Implementation: ccurve. py Fundamentals of Python: First Programs 40

Case Study (continued) • Implementation (continued): Fundamentals of Python: First Programs 41

Image Processing • Digital image processing includes the principles and techniques for the following: – The capture of images with devices such as flatbed scanners and digital cameras – The representation and storage of images in efficient file formats – Constructing the algorithms in image-manipulation programs such as Adobe Photoshop Fundamentals of Python: First Programs 42

Analog and Digital Information • Computers must use digital information which consists of discrete values – Example: Individual integers, characters of text, or bits • The information contained in images, sound, and much of the rest of the physical world is analog – Analog information contains a continuous range of values • Ticks representing seconds on an analog clock’s face represent an attempt to sample moments of time as discrete values (time itself is analog) Fundamentals of Python: First Programs 43

Sampling and Digitizing Images • A visual scene projects an infinite set of color and intensity values onto a two-dimensional sensing medium – If you sample enough of these values, digital information can represent an image more or less indistinguishable (to human eye) from original scene • Sampling devices measure discrete color values at distinct points on a two-dimensional grid – These values are pixels – As more pixels are sampled, the more realistic the resulting image will appear Fundamentals of Python: First Programs 44

Image File Formats • Once an image has been sampled, it can be stored in one of many file formats • A raw image file saves all of the sampled information • Data can be compressed to minimize its file size – JPEG (Joint Photographic Experts Group) • Uses lossless compression and a lossy scheme – GIF (Graphic Interchange Format) • Uses a lossy compression and a color palette of up to 256 of the most prevalent colors in the image Fundamentals of Python: First Programs 45

Image-Manipulation Operations • Image-manipulation programs either transform the information in the pixels or alter the arrangement of the pixels in the image • Examples: – – – – Rotate an image Convert an image from color to grayscale Blur all or part of an image Sharpen all or part of an image Control the brightness of an image Perform edge detection on an image Enlarge or reduce an image’s size Fundamentals of Python: First Programs 46

The Properties of Images • The coordinates of pixels in the two-dimensional grid of an image range from (0, 0) at the upper-left corner to (width-1, height-1) at lower-right corner – width/height are the image’s dimensions in pixels – Thus, the screen coordinate system for the display of an image is different from the standard Cartesian coordinate system that we used with Turtle graphics • The RGB color system is a common way of representing the colors in images Fundamentals of Python: First Programs 47

The images Module • Non-standard, open-source Python tool – Image class represents an image as a twodimensional grid of RGB values: smokey. gif Fundamentals of Python: First Programs 48

The images Module (continued) Fundamentals of Python: First Programs 49

A Loop Pattern for Traversing a Grid • Most of the loops we have used in this book have had a linear loop structure • Many image-processing algorithms use a nested loop structure to traverse a two-dimensional grid of pixels Fundamentals of Python: First Programs 50

A Loop Pattern for Traversing a Grid (continued) • Previous loop uses a row-major traversal – We use this template to develop many of the algorithms that follow: Fundamentals of Python: First Programs 51

A Word on Tuples • A pixel’s RGB values are stored in a tuple: Fundamentals of Python: First Programs 52

Converting an Image to Black and White • For each pixel, compute average of R/G/B values • Then, reset pixel’s color values to 0 (black) if the average is closer to 0, or to 255 (white) if the average is closer to 255: black. And. White. py Fundamentals of Python: First Programs 53

Converting an Image to Black and White (continued) Fundamentals of Python: First Programs 54

Converting an Image to Grayscale • Black and white photographs contain various shades of gray known as grayscale • Grayscale can be an economical scheme (the only color values might be 8, 16, or 256 shades of gray) • A simple method: – Problem: Does not reflect manner in which different color components affect human perception • Scheme needs to take differences in luminance into account gray. Scale. py Fundamentals of Python: First Programs 55

Converting an Image to Grayscale (continued) Fundamentals of Python: First Programs 56

Copying an Image • The method clone builds and returns a new image with the same attributes as the original one, but with an empty string as the filename Fundamentals of Python: First Programs 57

Blurring an Image • Pixilation can be mitigated by blurring Fundamentals of Python: First Programs 58

Edge Detection • Edge detection removes the full colors to uncover the outlines of the objects represented in the image edge. Detection. py Fundamentals of Python: First Programs 59

Edge Detection (continued) Fundamentals of Python: First Programs 60

Reducing the Image Size • The size and the quality of an image on a display medium depend on two factors: – Image’s width and height in pixels – Display medium’s resolution • Measured in pixels, or dots per inch (DPI) • The resolution of an image can be set before the image is captured – A higher DPI causes sampling device to take more samples (pixels) through the two-dimensional grid • A size reduction usually preserves an image’s aspect ratio image. Shrink. py Fundamentals of Python: First Programs 61

Reducing the Image Size (continued) • Reducing size throws away some pixel information Fundamentals of Python: First Programs 62

Summary • Object-based programming uses classes, objects, and methods to solve problems • A class specifies a set of attributes and methods for the objects of that class • The values of the attributes of a given object make up its state • A new object is obtained by instantiating its class • The behavior of an object depends on its current state and on the methods that manipulate this state • The set of a class’s methods is called its interface Fundamentals of Python: First Programs 63

Summary (continued) • Turtle graphics is a lightweight toolkit used to draw pictures in a Cartesian coordinate system • RGB system represents a color value by mixing integer components that represent red, green, and blue intensities • A grayscale system uses 8, 16, or 256 distinct shades of gray Fundamentals of Python: First Programs 64

Summary (continued) • Digital images are captured by sampling analog information from a light source, using a device such as a digital camera or a flatbed scanner – Can be stored in several formats, like JPEG and GIF • When displaying an image file, each color value is mapped onto a pixel in a two-dimensional grid – A nested loop structure is used to visit each position • Image-manipulation algorithms either transform pixels at given positions or create a new image using the pixel information of a source image Fundamentals of Python: First Programs 65