Raster (bitmap) images

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. A photo taken on a phone is stored as a raster image. What is a raster image made of?

A Lines and shapes described by maths formulas

B A grid of tiny pixels, each storing colour numbers

2. Another name for a raster image is a...

A Vector

B Bitmap

3. You zoom in a long way on a photo and see blocky squares. What are you seeing?

A Pixelation: the individual pixels of the raster image

B A fault where the file has been damaged

4. What does each pixel in a raster image store?

A Numbers that describe its colour

B A copy of the whole picture

5. Which of these is usually stored as a raster image?

A A photo of your friends at the beach

B A text message saying 'Hello'

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1raster image		AAnother name for a raster image, a picture stored pixel by pixel
2bitmap		BBitmaps get pixelated when zoomed in. Only the fixed pixels are enlarged, so the photo looks blocky.
3A photo is a raster image, so every pixel stores its own RGB colour numbers		CA picture made of a grid of tiny pixels, where each pixel stores its colour as numbers
4Zooming in on a raster image makes the pixels visible, so it looks blocky (pixelated)		Dpixel = (255, 128, 0)
5A raster image is stored as lines and shapes drawn from maths formulas		EThis describes a vector image. A raster image is stored as a grid of pixels, each with colour numbers.
6A photo stays perfectly smooth no matter how far you zoom in, because it is a bitmap		Fzoom 800% -> blocky squares

Definitions

raster image

Fill in the Blanks

Complete each line of code by filling in the missing parts.

img { image-rendering: _________; }

pixel(2, 3) ← [___, 0, 0]

FOR each _____ IN image DISPLAY colour of pixel END FOR

width ← 4 height ← 3 total ← width * ______

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A kind = "raster"

B width = 4

C height = 3

D pixels = width + height

Question 2

A photo_is_raster = False

B if photo_is_raster:

C print("Made of pixels")

Question 3

A zoom = 8

B pixel_size = 1 / zoom

C blocky = pixel_size > 1

Question 4

A grid = [[0, 255], [255, 0]

B row = grid[0]

C print(row[1])

Question 5

A for row in image:

B for pixel in row:

C print(pixel[3])

Answer Key

Raster (bitmap) images

Section A: Quick Questions

B — A grid of tiny pixels, each storing colour numbers

B — Bitmap

A — Pixelation: the individual pixels of the raster image

A — Numbers that describe its colour

A — A photo of your friends at the beach

Section B: Match the Pairs

raster image → A picture made of a grid of tiny pixels, where each pixel stores its colour as numbers

bitmap → Another name for a raster image, a picture stored pixel by pixel

A photo is a raster image, so every pixel stores its own RGB colour numbers → pixel = (255, 128, 0)

Zooming in on a raster image makes the pixels visible, so it looks blocky (pixelated) → zoom 800% -> blocky squares

A raster image is stored as lines and shapes drawn from maths formulas → This describes a vector image. A raster image is stored as a grid of pixels, each with colour numbers.

A photo stays perfectly smooth no matter how far you zoom in, because it is a bitmap → Bitmaps get pixelated when zoomed in. Only the fixed pixels are enlarged, so the photo looks blocky.

Section C: Definitions

raster image — A picture made of a grid of tiny pixels, each storing its colour as numbers. Also called a bitmap. Photos are raster images and look blocky (pixelated) when zoomed in.

Section D: Fill in the Blanks

<img src="photo.bmp" alt="A raster image">

img { image-rendering: pixelated; }

pixel(2, 3) ← [255, 0, 0]

FOR each pixel IN image
    DISPLAY colour of pixel
END FOR

width ← 4
height ← 3
total ← width * height

Section E: Spot the Error

D — The number of pixels in a grid is width multiplied by height (4 x 3 = 12), not added. It should be pixels = width * height.

A — Photos are raster images, so the value should be True. With False, the message about pixels would never print.

B — Zooming in makes each pixel appear bigger, so multiply by zoom. Dividing would shrink the pixels. It should be pixel_size = 1 * zoom.

A — The outer square bracket is never closed, so the grid of pixel values is a syntax error. It needs a final ] at the end.

C — Each pixel stores three colour numbers (red, green, blue) at positions 0, 1 and 2. Position 3 does not exist. It should be pixel[0], pixel[1] or pixel[2].