Unit 12.1A · Term 1

PIL Drawing Primitives

The ImageDraw module from PIL lets you draw graphic primitives — lines, rectangles, ellipses, polygons, and text — directly onto images using Python code.

Learning Objectives

12.6.2.3 Apply graphic primitives to create drawings

Lesson Presentation

12.1A-pil-drawing.pdf · Slides for classroom use

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Conceptual Anchor

The Canvas & Brush Analogy

Image.new() creates the canvas. ImageDraw.Draw(img) gives you a brush. You then call methods like draw.rectangle() or draw.ellipse() to paint shapes on the canvas — just like a graphics editor, but in code.

Rules & Theory

Setting Up a Drawing

from PIL import Image, ImageDraw

# Create canvas and draw object
img = Image.new("RGB", (400, 300), (255, 255, 255))  # white bg
draw = ImageDraw.Draw(img)

Drawing Primitives

Method	Parameters	Description
`draw.line()`	`[(x1,y1), (x2,y2)], fill, width`	Draw a straight line
`draw.rectangle()`	`[(x1,y1), (x2,y2)], fill, outline`	Draw a rectangle (top-left, bottom-right)
`draw.ellipse()`	`[(x1,y1), (x2,y2)], fill, outline`	Draw an ellipse within bounding box
`draw.polygon()`	`[(x1,y1), (x2,y2), ...], fill, outline`	Draw a polygon with any number of vertices
`draw.arc()`	`[(x1,y1), (x2,y2)], start, end, fill`	Draw an arc (part of ellipse outline)
`draw.point()`	`(x, y), fill`	Draw a single pixel
`draw.text()`	`(x, y), "text", fill, font`	Draw text on the image

Parameter Reference

Parameter	Meaning
`fill`	Interior color as RGB tuple, e.g. `(255, 0, 0)`
`outline`	Border color as RGB tuple
`width`	Line/border thickness in pixels
`(x1, y1)`	Top-left corner of bounding box
`(x2, y2)`	Bottom-right corner of bounding box

Worked Examples

1 Drawing Basic Shapes

from PIL import Image, ImageDraw

img = Image.new("RGB", (400, 300), (255, 255, 255))
draw = ImageDraw.Draw(img)

# Red rectangle
draw.rectangle([(50, 50), (150, 120)],
               fill=(255, 0, 0), outline=(0, 0, 0))

# Blue circle (ellipse in square bounding box)
draw.ellipse([(200, 50), (300, 150)],
             fill=(0, 0, 255), outline=(0, 0, 0))

# Green line
draw.line([(50, 200), (350, 200)],
          fill=(0, 128, 0), width=3)

img.save("shapes.png")

2 Drawing a Simple House

from PIL import Image, ImageDraw

img = Image.new("RGB", (400, 400), (135, 206, 235))  # sky blue bg
draw = ImageDraw.Draw(img)

# Ground
draw.rectangle([(0, 300), (400, 400)], fill=(34, 139, 34))

# House body
draw.rectangle([(100, 180), (300, 300)], fill=(210, 180, 140),
               outline=(0, 0, 0))

# Roof (triangle)
draw.polygon([(90, 180), (200, 100), (310, 180)],
             fill=(139, 69, 19), outline=(0, 0, 0))

# Door
draw.rectangle([(175, 230), (225, 300)], fill=(101, 67, 33),
               outline=(0, 0, 0))

# Window
draw.rectangle([(120, 210), (160, 250)], fill=(173, 216, 230),
               outline=(0, 0, 0))

# Sun
draw.ellipse([(320, 30), (380, 90)], fill=(255, 255, 0))

img.save("house.png")

3 Adding Text

from PIL import Image, ImageDraw, ImageFont

img = Image.new("RGB", (400, 200), (0, 0, 0))
draw = ImageDraw.Draw(img)

# Default font (basic)
draw.text((20, 80), "Hello, PIL!", fill=(255, 255, 255))

# Custom font (if available)
try:
    font = ImageFont.truetype("arial.ttf", 36)
    draw.text((20, 30), "Big Text", fill=(255, 200, 0),
              font=font)
except:
    pass

img.save("text_demo.png")

Common Pitfalls

Bounding Box — Not Center + Radius

Circles/ellipses use a bounding box [(x1,y1), (x2,y2)], NOT center + radius. For a circle at center (200, 150) with radius 50, use: [(150, 100), (250, 200)].

Tasks

Apply

Draw a traffic light: black rectangle with three circles (red, yellow, green) inside.

Apply

Draw a smiley face using ellipses and arcs. Save it as "smiley.png".

Create

Create a landscape scene (sky, ground, sun, trees) using at least 5 different drawing primitives.

Self-Check Quiz

Q1: How do you create a draw object?

draw = ImageDraw.Draw(img) — pass the image you want to draw on.

Q2: How do you draw a circle with PIL?

Use draw.ellipse() with a square bounding box, e.g. draw.ellipse([(50,50),(150,150)], fill="red").

Q3: What's the difference between fill and outline?

fill is the interior color of the shape. outline is the border color.