← ACARA Digital Technologies Years 5–6

Reading a pixel grid row by row

Read a pixel grid in order: start at the top row, go left to right across it, then move down to the next row until the grid ends.

Part of: ACARA Digital Technologies Years 5–6 — Representing Data with Numbers — Module 9, ACARA Digital Technologies Years 7–8 — Representing Text, Images and Sound — Module 25

Understanding Reading a pixel grid row by row in ACARA Digital Technologies Years 5–6

What it does: Counting the pixels in a grid means multiplying the number of rows by the number of columns. The first group before the first slash is the top row, written from left to right, and the next rows follow below it. Rows are read in order from top to bottom, one at a time, with no skipping. Multiply the rows by the columns: 4 x 5 = 20. Adding them (4 + 5 = 9) is a common mistake. Every pixel gets its own number, so a 3 by 3 grid gives 9 numbers. A row of 4 pixels means a new row starts after every 4 digits. This marks where each row ends.

Common mistakes: A pixel grid is read from left to right across each row. The line should say 'Read left to right, then go down'.}. Reading always starts at the top row, so the first pixel is the top-left one. The line should say 'Start at the top-left pixel'.

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Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

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This module's key terms are also in a printable crossword (Modules 44–57) and word search (Modules 44–71).

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Each concept is reinforced from every angle — learned, then applied, then tested.

Learning
Duo
Where do you start when reading a pixel grid?
At the bottom-right pixelAt the top-left pixel
Matches
Read the grid from the bottom row up to the top row
↓
A pixel grid is read from the top row down, not from the bottom up. Start at the top row and move down.
Applying
Meanings
Term
row by row
Meaning
Read a pixel grid in order: start at the top row, go left to right across it, then move down to the next row until the grid ends.
Practice
101
Testing
Gaps
row ←
Check Answer
Spots
2Start at the top row
3Read right to left, then go down

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Quick Questions

1. Where do you start when reading a pixel grid?
A. At the bottom-right pixel
B. At the top-left pixel ✓
A pixel grid is read from the top row first, starting at the left, just like reading a page of a book.
2. Which way do you read across a row of pixels?
A. Left to right ✓
B. Right to left
Each row is read from left to right. Then you move down to the next row.
3. After you finish the top row, which row do you read next?
A. The row just below it ✓
B. The row at the very bottom
Rows are read in order from top to bottom, one at a time, with no skipping.
4. A grid has 4 rows and 5 columns. How many pixels does it have?
A. 20 pixels ✓
B. 9 pixels
Multiply the rows by the columns: 4 x 5 = 20. Adding them (4 + 5 = 9) is a common mistake.
5. A grid is 3 pixels wide and 3 pixels tall. How many numbers do you write down when you read it?
A. 3 numbers, one for each row
B. 9 numbers, one for each pixel ✓
Every pixel gets its own number, so a 3 by 3 grid gives 9 numbers.

Match the Pairs

row by row → Read the pixels starting at the top row, going left to right, then moving down to the next row
0 1 1 0 / 1 0 0 1 / 0 1 1 0 → A 4 by 3 grid written as 3 rows of 4 pixels, with a slash marking where each row ends
A grid with 3 rows and 4 columns has 12 pixels, because you multiply the rows by the columns → 3 * 4 = 12
Reading starts at the top row and goes left to right, so the first row of the picture is written first → 1 0 1 / 0 1 0 / 1 0 1
Read the grid from the bottom row up to the top row → A pixel grid is read from the top row down, not from the bottom up. Start at the top row and move down.
A grid with 4 columns and 3 rows has 4 + 3 = 7 pixels → The pixels are counted by multiplying, not adding. The grid has 4 * 3 = 12 pixels.

Key Term

row by row
Read a pixel grid in order: start at the top row, go left to right across it, then move down to the next row until the grid ends.

Fill in the Blanks

1. row ← 1 READ pixels across row 1, left to right
Hint: Type the number of the very first row, the one at the top of the grid.
2. width ← 4 height ← 3 total ← width * height
Hint: Type the operator that multiplies the pixels across by the rows down to count every pixel.
3. FOR each row from top to bottom FOR each pixel from left to right READ the pixel
Hint: Type the word for each horizontal line of pixels that the outer loop steps through.
4. image ← "0110/1001/0110"
Hint: Type the symbol that marks where the first row ends and the next row starts.
5. START at the top row READ left to right across the row MOVE down to the next row
Hint: Type the position where reading a pixel grid always begins.

Spot the Error

Question 1
A Grid: 3 columns, 2 rows
B Start at the top row
C Read right to left, then go down
D Stop after row 2
Line C — A pixel grid is read from left to right across each row. The line should say 'Read left to right, then go down'.}
Question 2
A Start at the bottom-left pixel
B Read across the row
C Move down to the next row
D Stop at the last pixel
Line A — Reading always starts at the top row, so the first pixel is the top-left one. The line should say 'Start at the top-left pixel'.
Question 3
A Grid: 5 columns, 4 rows
B Pixels in one row: 5
C Total pixels: 5 + 4 = 9
Line C — To count all the pixels, multiply the pixels in one row by the number of rows. It should be 5 x 4 = 20, not 5 + 4.
Question 4
A Data: 0 1 1 | 1 0 0 | 0 0 1
B Each | shows a new column
C So the grid has 3 rows
D Each row has 3 pixels
Line B — In this data the | marks where one row ends and the next row starts. It does not show a new column. The line should say 'Each | shows a new row'.
Question 5
A Grid: 4 columns, 3 rows
B Row 1 is the top row
C Row 3 is the bottom row
D Last pixel: row 4, column 3
Line D — The grid has only 3 rows and 4 columns. The last pixel is at the end of the bottom row: row 3, column 4. Row 4 does not exist.

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