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Manipulating Images

407

lines you’re drawing. The optional

fill

argument is the color of the lines,

as an RGBA tuple or color name. The optional

width

argument is the width

of the lines and defaults to 1 if left unspeciﬁed.

rectangles

The

rectangle(xy, fill, outline)

method draws a rectangle. The

argu-

ment is a box tuple of the form

(left, top, right, bottom)

. The

left

and

top

values specify the x- and y-coordinates of the upper-left corner of the rect-

angle, while

right

and

bottom

specify the lower-right corner. The optional

fill

argument is the color that will ﬁll the inside of the rectangle. The

optional

outline

argument is the color of the rectangle’s outline.

Ellipses

The

ellipse(xy, fill, outline)

method draws an ellipse. If the width and

height of the ellipse are identical, this method will draw a circle. The

argument is a box tuple (

left

top

right

bottom

) that represents a box that

precisely contains the ellipse. The optional

fill

argument is the color of the

inside of the ellipse, and the optional

outline

argument is the color of the

ellipse’s outline.

Polygons

The

polygon(xy, fill, outline)

method draws an arbitrary polygon. The

argument is a list of tuples, such as

[(x, y), (x, y), ...]

, or integers, such

[x1, y1, x2, y2, ...]

, representing the connecting points of the polygon’s

sides. The last pair of coordinates will be automatically connected to the

ﬁrst pair. The optional

fill

argument is the color of the inside of the poly-

gon, and the optional

outline

argument is the color of the polygon’s outline.

Drawing Example

Enter the following into the interactive shell:

>>> from PIL import Image, ImageDraw

>>> im = Image.new('RGBA', (200, 200), 'white')

>>> draw = ImageDraw.Draw(im)

u >>> draw.line([(0, 0), (199, 0), (199, 199), (0, 199), (0, 0)], fill='black')

v >>> draw.rectangle((20, 30, 60, 60), fill='blue')

w >>> draw.ellipse((120, 30, 160, 60), fill='red')

x >>> draw.polygon(((57, 87), (79, 62), (94, 85), (120, 90), (103, 113)),

fill='brown')

y >>> for i in range(100, 200, 10):

draw.line([(i, 0), (200, i - 100)], fill='green')

>>> im.save('drawing.png')

After making an

Image

object for a 200×200 white image, passing it to

ImageDraw.Draw()

to get an

ImageDraw

object, and storing the

ImageDraw

object

draw

, you can call drawing methods on

draw

. Here we make a thin, black

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408

Chapter 17

outline at the edges of the image u, a blue rectangle with its top-left corner

at (20, 30) and bottom-right corner at (60, 60) v, a red ellipse deﬁned by a

box from (120, 30) to (160, 60) w, a brown polygon with ﬁve points x, and

a pattern of green lines drawn with a

for

loop y. The resulting drawing.png

ﬁle will look like Figure 17-14.

Figure 17-14: The resulting drawing‮png

image

There are several other shape-drawing methods for

ImageDraw

objects.

The full documentation is available at http://pillow.readthedocs.org/en/latest/

reference/ImageDraw.html.

Drawing Text

The

ImageDraw

object also has a

text()

method for drawing text onto an

image. The

text()

method takes four arguments:

text

fill

, and

font

• The

argument is a two-integer tuple specifying the upper-left corner

of the text box.

• The

text

argument is the string of text you want to write.

• The optional

fill

argument is the color of the text.

• The optional

font

argument is an

ImageFont

object, used to set the type-

face and size of the text. This is described in more detail in the next

section.

Since it’s often hard to know in advance what size a block of text will

be in a given font, the

ImageDraw

module also offers a

textsize()

method.

Its ﬁrst argument is the string of text you want to measure, and its second

argument is an optional

ImageFont

object. The

textsize()

method will then

return a two-integer tuple of the width and height that the text in the given

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Manipulating Images

409

font would be if it were written onto the image. You can use this width and

height to help you calculate exactly where you want to put the text on your

image.

The ﬁrst three arguments for

text()

are straightforward. Before we use

text()

to draw text onto an image, let’s look at the optional fourth argument,

the

ImageFont

object.

Both

text()

and

textsize()

take an optional

ImageFont

object as their

ﬁnal arguments. To create one of these objects, ﬁrst run the following:

>>> from PIL import ImageFont

Now that you’ve imported Pillow’s

ImageFont

module, you can call the

ImageFont.truetype()

function, which takes two arguments. The ﬁrst argu-

ment is a string for the font’s TrueType ﬁle—this is the actual font ﬁle that

lives on your hard drive. A TrueType ﬁle has the .ttf ﬁle extension and can

usually be found in the following folders:

• On Windows: C:\Windows\Fonts

• On OS X: /Library/Fonts and /System/Library/Fonts

• On Linux: /usr/share/fonts/truetype

You don’t actually need to enter these paths as part of the TrueType

ﬁle string because Python knows to automatically search for fonts in these

directories. But Python will display an error if it is unable to ﬁnd the font

you speciﬁed.

The second argument to

ImageFont.truetype()

is an integer for the font

size in points (rather than, say, pixels). Keep in mind that Pillow creates

PNG images that are 72 pixels per inch by default, and a point is 1/72 of

an inch.

Enter the following into the interactive shell, replacing

FONT_FOLDER

with

the actual folder name your operating system uses:

>>> from PIL import Image, ImageDraw, ImageFont

>>> import os

u >>> im = Image.new('RGBA', (200, 200), 'white')

v >>> draw = ImageDraw.Draw(im)

w >>> draw.text((20, 150), 'Hello', fill='purple')

>>> fontsFolder = 'FONT_FOLDER' # e.g. ‘/Library/Fonts’

x >>> arialFont = ImageFont.truetype(os.path.join(fontsFolder, 'arial.ttf'), 32)

y >>> draw.text((100, 150), 'Howdy', fill='gray', font=arialFont)

>>> im.save('text.png')

After importing

Image

ImageDraw

ImageFont

, and

, we make an

Image

object for a new 200×200 white image u and make an

ImageDraw

object from

the

Image

object v. We use

text()

to draw Hello at (20, 150) in purple w. We

didn’t pass the optional fourth argument in this

text()

call, so the typeface

and size of this text aren’t customized.

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410

Chapter 17

To set a typeface and size, we ﬁrst

store the folder name (like /Library/

Fonts) in

fontsFolder

. Then we call

ImageFont.truetype()

, passing it the .ttf

ﬁle for the font we want, followed by

an integer font size x. Store the

Font

object you get from

ImageFont.truetype()

in a variable like

arialFont

, and then

pass the variable to

text()

in the ﬁnal

keyword argument. The

text()

call at y

draws Howdy at (100, 150) in gray in

32-point Arial.

The resulting text.png ﬁle will look

like Figure 17-15.

Summary

Images consist of a collection of pixels, and each pixel has an RGBA value

for its color and its addressable by x- and y-coordinates. Two common image

formats are JPEG and PNG. The

pillow

module can handle both of these

image formats and others.

When an image is loaded into an

Image

object, its width and height

dimensions are stored as a two-integer tuple in the

size

attribute. Objects of the

Image

data type also have methods for common image manipulations:

crop()

copy()

paste()

resize()

rotate()

, and

transpose()

. To save the

Image

object to

an image ﬁle, call the

save()

method.

If you want your program to draw shapes onto an image, use

ImageDraw

methods to draw points, lines, rectangles, ellipses, and polygons. The mod-

ule also provides methods for drawing text in a typeface and font size of

your choosing.

Although advanced (and expensive) applications such as Photoshop

provide automatic batch processing features, you can use Python scripts to

do many of the same modiﬁcations for free. In the previous chapters, you

wrote Python programs to deal with plaintext ﬁles, spreadsheets, PDFs, and

other formats. With the

pillow

module, you’ve extended your programming

powers to processing images as well!

Practice Questions

1. What is an RGBA value?

2. How can you get the RGBA value of

'CornflowerBlue'

from the

Pillow

module?

3. What is a box tuple?

4. What function returns an

Image

object for, say, an image ﬁle named

zophie.png?

Figure 17-15: The resulting text‮png

image

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Manipulating Images

411

5. How can you ﬁnd out the width and height of an

Image

object’s image?

6. What method would you call to get

Image

object for a 100×100 image,

excluding the lower left quarter of it?

7. After making changes to an

Image

object, how could you save it as an

image ﬁle?

8. What module contains Pillow’s shape-drawing code?

Image

objects do not have drawing methods. What kind of object does?

How do you get this kind of object?

Practice Projects

For practice, write programs that do the following.

Extending and Fixing the Chapter Project Programs

The resizeAndAddLogo.py program in this chapter works with PNG and JPEG

ﬁles, but Pillow supports many more formats than just these two. Extend

resizeAndAddLogo.py to process GIF

and BMP images as well.

Another small issue is that the

program modiﬁes PNG and JPEG

ﬁles only if their ﬁle extensions are

set in lowercase. For example, it will

process zophie.png but not zophie.PNG.

Change the code so that the ﬁle

extension check is case insensitive.

Finally, the logo added to the

bottom-right corner is meant to be

just a small mark, but if the image is

about the same size as the logo itself,

the result will look like Figure 17-16.

Modify resizeAndAddLogo.py so that

the image must be at least twice the

width and height of the logo image

before the logo is pasted. Other wise,

it should skip adding the logo.

Identifying Photo Folders on the Hard Drive

I have a bad habit of transferring ﬁles from my digital camera to temporary

folders somewhere on the hard drive and then forgetting about these fold-

ers. It would be nice to write a program that could scan the entire hard

drive and ﬁnd these leftover “photo folders.”

Write a program that goes through every folder on your hard drive and

ﬁnds potential photo folders. Of course, ﬁrst you’ll have to deﬁne what you

consider a “photo folder” to be; let’s say that it’s any folder where more than

half of the ﬁles are photos. And how do you deﬁne what ﬁles are photos?

Figure 17-16: When the image isn’t much

larger than the logo, the results look ugly.

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412

Chapter 17

First, a photo ﬁle must have the ﬁle extension .png or .jpg. Also, photos

are large images; a photo ﬁle’s width and height must both be larger than

500 pixels. This is a safe bet, since most digital camera photos are several

thousand pixels in width and height.

As a hint, here’s a rough skeleton of what this program might look like:

#! python3

# Import modules and write comments to describe this program.

for foldername, subfolders, filenames in os.walk('C:\\'):

numPhotoFiles = 0

numNonPhotoFiles = 0

for filename in filenames:

# Check if file extension isn't .png or .jpg.

if TODO:

numNonPhotoFiles += 1

continue # skip to next filename

# Open image file using Pillow.

# Check if width & height are larger than 500.

if TODO:

# Image is large enough to be considered a photo.

numPhotoFiles += 1

else:

# Image is too small to be a photo.

numNonPhotoFiles += 1

# If more than half of files were photos,

# print the absolute path of the folder.

if TODO:

print(TODO)

When the program runs, it should print the absolute path of any photo

folders to the screen.

Custom Seating Cards

Chapter 13 included a practice project to create custom invitations from

a list of guests in a plaintext ﬁle. As an additional project, use the

pillow

module to create images for custom seating cards for your guests. For

each of the guests listed in the guests.txt ﬁle from the resources at http://

nostarch.com/automatestuff/, generate an image ﬁle with the guest name and

some ﬂowery decoration. A public domain ﬂower image is available in the

resources at http://nostarch.com/automatestuff/.

To ensure that each seating card is the same size, add a black rectangle

on the edges of the invitation image so that when the image is printed out,

there will be a guideline for cutting. The PNG ﬁles that Pillow produces are

set to 72 pixels per inch, so a 4×5-inch card would require a 288×360-pixel

image.

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Co n t r o l l i n g t h e

ke y B o A r D A n D m o u S e

wi t h g u i A u t o m A t i o n

Knowing various Python modules for edit-

ing spreadsheets, downloading ﬁles, and

launching programs is useful, but some-

times there just aren’t any modules for the

applications you need to work with. The ultimate

tools for automating tasks on your computer are pro-

grams you write that directly control the keyboard

and mouse. These programs can control other applications by sending

them virtual keystrokes and mouse clicks, just as if you were sitting at your

computer and interacting with the applications yourself. This technique

is known as graphical user interface automation, or GUI automation for short.

With GUI automation, your programs can do anything that a human user

sitting at the computer can do, except spill coffee on the keyboard.

Think of GUI automation as programming a robotic arm. You can

program the robotic arm to type at your keyboard and move your mouse

for you. This technique is particularly useful for tasks that involve a lot of

mindless clicking or ﬁlling out of forms.

414

Chapter 18

The

pyautogui

module has functions for simulating mouse movements,

button clicks, and scrolling the mouse wheel. This chapter covers only a

subset of PyAutoGUI’s features; you can ﬁnd the full documentation at

http://pyautogui.readthedocs.org/.

Installing the pyautogui Module

The

pyautogui

module can send virtual keypresses and mouse clicks to

Windows, OS X, and Linux. Depending on which operating system you’re

using, you may have to install some other modules (called dependencies)

before you can install PyAutoGUI.

• On Windows, there are no other modules to install.

• On OS X, run

sudo pip3 install pyobjc-framework-Quartz

sudo pip3

install pyobjc-core

, and then

sudo pip3 install pyobjc

• On Linux, run

sudo pip3 install python3-xlib

sudo apt-get install scrot

sudo apt-get install python3-tk

, and

sudo apt-get install python3-dev

(Scrot is a screenshot program that PyAutoGUI uses.)

After these dependencies are installed, run

pip install pyautogui

(or

pip3

on OS X and Linux) to install PyAutoGUI.

Appendix A has complete information on installing third-party modules.

To test whether PyAutoGUI has been installed correctly, run

import pyautogui

from the interactive shell and check for any error messages.

Staying on Track

Before you jump in to a GUI automation, you should know how to escape

problems that may arise. Python can move your mouse and type keystrokes

at an incredible speed. In fact, it might be too fast for other programs to

keep up with. Also, if something goes wrong but your program keeps mov-

ing the mouse around, it will be hard to tell what exactly the program is

doing or how to recover from the problem. Like the enchanted brooms from

Disney’s The Sorcerer’s Apprentice, which kept ﬁlling—and then overﬁlling—

Mickey’s tub with water, your program could get out of control even though

it’s following your instructions perfectly. Stopping the program can be difﬁ-

cult if the mouse is moving around on its own, preventing you from clicking

the IDLE window to close it. Fortunately, there are several ways to prevent

or recover from GUI automation problems.

Shutting Down Everything by Logging Out

Perhaps the simplest way to stop an out-of-control GUI automation program

is to log out, which will shut down all running programs. On Windows and

Linux, the logout hotkey is

ctrl

alt

del

. On OS X, it is z-

shift

option

-Q.

By logging out, you’ll lose any unsaved work, but at least you won’t have to

wait for a full reboot of the computer.

Controlling the Keyboard and Mouse with GUI Automation

415

Pauses and Fail-Safes

You can tell your script to wait after every function call, giving you a short

window to take control of the mouse and keyboard if something goes wrong.

To do this, set the

pyautogui.PAUSE

variable to the number of seconds you

want it to pause. For example, after setting

pyautogui.PAUSE = 1.5

, every

PyAutoGUI function call will wait one and a half seconds after performing

its action. Non-PyAutoGUI instructions will not have this pause.

PyAutoGUI also has a fail-safe feature. Moving the mouse cursor to the

upper-left corner of the screen will cause PyAutoGUI to raise the

pyautogui

.FailSafeException

exception. Your program can either handle this excep-

tion with

try

and

except

statements or let the exception crash your program.

Either way, the fail-safe feature will stop the program if you quickly move

the mouse as far up and left as you can. You can disable this feature by set-

ting

pyautogui.FAILSAFE = False

. Enter the following into the interactive shell:

>>> import pyautogui

>>> pyautogui.PAUSE = 1

>>> pyautogui.FAILSAFE = True

Here we import

pyautogui

and set

pyautogui.PAUSE

for a one-second

pause after each function call. We set

pyautogui.FAILSAFE

True

to enable

the fail-safe feature.

controlling mouse movement

In this section, you’ll learn how to move the mouse and track its position

on the screen using PyAutoGUI, but ﬁrst you need to understand how

PyAutoGUI works with coordinates.

The mouse functions

of PyAutoGUI use x- and

y- coordinates. Fig ure 18-1

shows the coordinate system

for the computer screen; it’s

similar to the coordinate

system used for images, dis-

cussed in Chapter 17. The

origin, where x and y are

both zero, is at the upper-

left corner of the screen.

The x- coordinates increase

going to the right, and the

y- coordinates increase going

down. All coordinates are

positive integers; there are

no negative coordinates.

(0,0)

(1919,0)

(0,1079)

(1919,1079)

x increases

y increases

Figure 18-1: The coordinates of a computer screen

with 1920×1080 resolution

416

Chapter 18

Your resolution is how many pixels wide and tall your screen is. If your

screen’s resolution is set to 1920×1080, then the coordinate for the upper-

left corner will be (0, 0), and the coordinate for the bottom-right corner

will be (1919, 1079).

The

pyautogui.size()

function returns a two-integer tuple of the screen’s

width and height in pixels. Enter the following into the interactive shell:

>>> import pyautogui

>>> pyautogui.size()

(1920, 1080)

>>> width, height = pyautogui.size()

pyautogui.size()

returns

(1920, 1080)

on a computer with a 1920×1080

resolution; depending on your screen’s resolution, your return value may be

different. You can store the width and height from

pyautogui.size()

in vari-

ables like

width

and

height

for better readability in your programs.

Moving the Mouse

Now that you understand screen coordinates, let’s move the mouse. The

pyautogui.moveTo()

function will instantly move the mouse cursor to a speciﬁed

position on the screen. Integer values for the x- and y-coordinates make up

the function’s ﬁrst and second arguments, respectively. An optional

duration

integer or ﬂoat keyword argument speciﬁes the number of seconds it should

take to move the mouse to the destination. If you leave it out, the default is

for instantaneous movement. (All of the

duration

keyword arguments in

PyAutoGUI functions are optional.) Enter the following into the interactive

shell:

>>> import pyautogui

>>> for i in range(10):

pyautogui.moveTo(100, 100, duration=0.25)

pyautogui.moveTo(200, 100, duration=0.25)

pyautogui.moveTo(200, 200, duration=0.25)

pyautogui.moveTo(100, 200, duration=0.25)

This example moves the mouse cursor clockwise in a square pattern

among the four coordinates provided a total of ten times. Each movement

takes a quarter of a second, as speciﬁed by the

duration=0.25

keyword argu-

ment. If you hadn’t passed a third argument to any of the

pyautogui.moveTo()

calls, the mouse cursor would have instantly teleported from point to point.

The

pyautogui.moveRel()

function moves the mouse cursor relative to

its current position. The following example moves the mouse in the same

square pattern, except it begins the square from wherever the mouse hap-

pens to be on the screen when the code starts running:

>>> import pyautogui

>>> for i in range(10):

pyautogui.moveRel(100, 0, duration=0.25)

pyautogui.moveRel(0, 100, duration=0.25)

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