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Course 288 · Digital course 51

Process Image Pixels with Canvas

Build a local original 4×4-to-64×64 pixel image tool with RGBA inspection, grayscale and threshold filters, preserved alpha and checked PNG export. Work from supplied original examples and check changed cases.

Before you start

Review Build your first website and introductory JavaScript.

Add JavaScript Interactivity to a Web Page See everything you’ll need

Free download · Original practice data · No external account required. Download the starter pack

What you’ll leave with

A local original 4×4-to-64×64 pixel image tool with RGBA inspection, grayscale and threshold filters, preserved alpha and checked PNG export.

Start course Start without an account. Sign in to save lesson progress across devices.

Your project

Start with the practice files. Build your project one lesson at a time.

Practice files are free without an account. Sign in to save your project record in My Proof: a description, checklist, and optional work link. Keep the original files in your own app or notebook; saving a project record does not upload them.

  1. Get your materialsDownload practice filesSupplied practice cases, a blank working record, complete lesson instructions, and annotated worked examples.
  2. Make your projectView the project checklist Work in your own notebook, document, or software. Use the supplied practice examples when you prefer.
  3. Keep a private recordSave a project record Sign in to save a description and checklist, then return to update them.
Course handbook

Know the route before you begin.

Here’s what you’ll need and what you’ll make. You can return to this guide during any lesson.

Who this is for

Learners ages 14+ and adults ready for the named prerequisite; no employment or private records required.

Prepare before lesson one
  • Review Build your first website and introductory JavaScript.
  • Use a current browser, image viewer, Python 3 local server, and optional Node.js for arithmetic assertions. No accounts, packages, or downloaded source photos needed.
  • Use only the original supplied pixel buffer.
Your final project

Finish with proof you can use.

A local original 4×4-to-64×64 pixel image tool with RGBA inspection, grayscale and threshold filters, preserved alpha and checked PNG export.

Save a project record in My Proof
See project checklist and review criteria

Keep your working files in your own notebook or software. Save a private description, checklist, and work link in My Proof.

What to include

  • Produce a checked RGBA and coordinate-to-offset inspection table.
  • Demonstrate separate source/result buffers and a working original reset.
  • Calculate and verify equal-channel grayscale with alpha unchanged.
  • Produce a below/equal/above threshold matrix with preserved alpha.
  • Create and inspect the actual 64×64 PNG with intended crisp scaling and alpha behavior.
  • Deliver source, checked channel math, actual rendered/export evidence, and honest unavailable checks.

Review and revise

Use these criteria to check your work and choose what to improve.

  • The implementation or declared simulation follows the supplied contract and retains inspectable original inputs.
  • Normal, boundary and rejected cases are recorded with expected versus observed results.
  • The changed case has a correct explanation and does not rely on hidden state.
  • The project includes source, outputs, instructions and honest tool, privacy and verification limits.
Three ideas to help you along the way
Three useful ideas

The rules behind the steps.

01

State the contract

Name inputs, permitted states and observable outputs before editing the implementation.

02

Preserve the evidence

Keep the actual source, changed input and expected/observed record so someone can repeat the work.

03

Test the boundary

Check a rejection or changed case and distinguish local practice from real service or native-tool behavior.

What do these words mean?
Key words

Key terms worth knowing.

RGBA
Red, green, blue, and alpha channels for a pixel.
row-major
Pixels stored row by row in sequence.
threshold
A cutoff that assigns values to classes.
alpha
The channel controlling opacity.
interpolation
Creating intermediate values while scaling an image.
Your route

6 lessons.
One useful project.

Work in order the first time. Each lesson makes something the next lesson can use.

  1. 1
    Up next

    Read RGBA and pixel coordinates

    Produce a checked RGBA and coordinate-to-offset inspection table.

  2. 2
    19 min

    Keep an original buffer and a new result

    Demonstrate separate source/result buffers and a working original reset.

  3. 3
    22 min

    Calculate an equal-channel grayscale

    Calculate and verify equal-channel grayscale with alpha unchanged.

  4. 4
    19 min

    Apply a threshold with a stated boundary

    Produce a below/equal/above threshold matrix with preserved alpha.

  5. 5
    24 min

    Scale deliberately and inspect PNG export

    Create and inspect the actual 64×64 PNG with intended crisp scaling and alpha behavior.

  6. 6
    26 min

    Deliver pixel arithmetic and rendered evidence

    Deliver source, checked channel math, actual rendered/export evidence, and honest unavailable checks.

Use the tools

Tools to help you practice.

See all tools
ZIP · practice files

Process Image Pixels with Canvas practice files

Supplied practice cases, a blank working record, complete lesson instructions, and annotated worked examples.

Text worksheet

Your course project worksheet

A downloadable text worksheet with each lesson’s working output, space for your answers, and the shared final-project checklist. Save your own copy.

Source transparency

Sources and further study.

Explore the references behind the lessons and take your learning further. Source notes explain access and reuse.

developer.mozilla.org — Pixel_manipulation_with_canvas
Source & access notes · checked 2026-10-01

Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.

Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.

Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.

developer.mozilla.org — putImageData
Source & access notes · checked 2026-10-01

Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.

Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.

Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.

developer.mozilla.org — toBlob
Source & access notes · checked 2026-10-01

Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.

Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.

Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.

Ready when you are

Start with the first useful move.

You’ll always know what to do, what to make, and where to go next.

Start lesson one