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

Transcription

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

2 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

3 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

4 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

5 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 1960s 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

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

7 Turtle Operations Fundamentals of Python: First Programs 7

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

9 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.bk(distance) turtle.backward(distance) turtle.right(angle) turtle.rt(angle) turtle.left(angle) turtle.lt(angle) turtle.goto(x, y=none) turtle.setpos(x, y=none) turtle.setposition(x, y=none) integer or float integer or float integer or float x a number or a pair/vector of numbers y a number or None Move the turtle backward by distance, opposite to the direction the turtle is headed. Do not change the turtle s heading 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, 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 If y is None, x must be a pair of coordinates or a Vec2D (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

10 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) turtle.home() turtle.circle(radius, extent=non e, steps=none integer or float radius a number extent a number (or None) steps an integer (or None) 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 west south south 270 west Move turtle to the origin coordinates (0,0) and set its heading to its start-orientation (which depends on the mode, see mode()) 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. Fundamentals of Python: First Programs 10

11 Turtle Motion (Move and Draw 3) turtle.dot(size=non e, *color) turtle.stamp() turtle.clearstamp(sta mpid) turtle.clearstamps(n =None) turtle.undo() turtle.speed(speed= None) size an integer >= 1 (if given) color a colorstring or a numeric color tuple stampid an integer, must be return value of previous stamp() call n an integer (or None) speed an integer in the range or a speedstring (see below) 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). Delete stamp with given stampid. 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 Undo (repeatedly) the last turtle action(s). Number of available undo actions is determined by the size of the undobuffer.. Set the turtle s speed to an integer value in the range 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. Fundamentals of Python: First Programs 11

12 Tell Turtle s State turtle.position() turtle.pos() turtle.towards(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 Return the turtle s current location (x,y) (as a Vec2D vector). 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() 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 Return the turtle s current heading (value depends on the turtle mode, see mode()) Return the distance from the turtle to (x,y), the given vector, or the given other turtle, in turtle step units.. Fundamentals of Python: First Programs 12

13 Drawing State turtle.pendown() turtle.pd() turtle.down() turtle.penup() turtle.pu() turtle.up() turtle.pensize(width=none) turtle.width(width=none) turtle.isdown() turtle.pen(pen=none, **pen dict) width a positive number pen a dictionary with some or all of the below listed keys pendict one or more keywordarguments with the below listed keys as keywords Pull the pen down drawing when moving.. Pull the pen up no drawing when moving. 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. 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 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. Fundamentals of Python: First Programs 13

14 Color Control turtle.pencolor(*args) Return or set the pencolor. Four input formats are allowed: 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 "#33cc8c". 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 the fillcolor. Four input formats are allowed: fillcolor() Return the current fillcolor as color specification string, possibly in tuple format (see 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 "#33cc8c". 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(colorstring1, colorstring2), color((r1,g1,b1), (r2,g2,b2))equivalent to pencolor(colorstring1) and fillcolor(colorstring2) and analogously if the other input format is used. Fundamentals of Python: First Programs 14

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

16 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() turtle.write(arg, move=false, align="left", font=("arial", 8, "normal")) arg object to be written to the TurtleScreen move True/False align one of the strings left, center or right font a triple (fontname, fontsize, fonttype) 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. 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. Fundamentals of Python: First Programs 16

17 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() turtle.isvisible() Make the turtle visible. Return True if the Turtle is shown, False if it s hidden. Fundamentals of Python: First Programs 17

18 Window Control turtle.bgcolor(*args) turtle.clear() turtle.clearscreen() turtle.reset() turtle.resetscreen() turtle.screensize(canvwidth=non e, canvheight=none, bg=none) args a color string or three numbers in the range 0..colormode or a 3-tuple of such numbers 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 Set or return background color of the TurtleScreen Delete all drawings and all turtles from the TurtleScreen. Reset the now empty TurtleScreen to its initial state: white background, no background image, no event bindings and tracing on. Reset all Turtles on the Screen to their initial state. 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. Fundamentals of Python: First Programs 18

19 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

20 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>) drawsquare.py Fundamentals of Python: First Programs 20

21 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

22 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

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

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

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

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

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

28 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 maximum saturation of a color component 0 total absence of that color component A true color system Fundamentals of Python: First Programs 28

29 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 2 24 (16,777,216) Fundamentals of Python: First Programs 29

30 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

31 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

32 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

33 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, Scene1.gif, Scene2.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("backgroundpic.gif") and the name of your background pictures. Fundamentals of Python: From First Programs Through Data Structures 33

34 Using Multiple Turtles Instantiate more than one turtle, for example: t = Turtle() t2 = Turtle() t3 = Turtle() Register and associate the turtles to shapes (.gif) t.screen.register_shape( picture1name.gif") t2.screen.register_shape( picture2name.gif") t3.screen.register_shape( picture3name.gif") Set the shape for each turtle t.shape( picture1name.gif") t2.shape( picture2name.gif") t3.shape( picture3name.gif") Use transparent GIF files for turtle shapes. Fundamentals of Python: From First Programs Through Data Structures 34

35 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)) t2.fd(random.randint(1,3)) t3.fd(random.randint(1,4)) screen.delay(3) Fundamentals of Python: From First Programs Through Data Structures 35

36 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

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

38 Case Study: Recursive Patterns in Request: Fractals (continued) 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

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

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

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

42 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

43 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

44 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

45 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

46 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

47 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

48 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

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

50 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

51 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

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

53 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: blackandwhite.py Fundamentals of Python: First Programs 53

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

55 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 grayscale.py Fundamentals of Python: First Programs 55

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

57 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

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

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

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

61 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 imageshrink.py Fundamentals of Python: First Programs 61

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

63 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

64 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

65 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