Be able to adjust the brightness of an image

Resources → Subject Notes → Information Communication Technology ICT → Lesson Plan

Topic 12 – Images (ICT 0417)

Learning Objective

Students will be able to edit raster images using the eight required operations – place, resize, crop, rotate, reflect, adjust brightness & contrast, group/layer, and reduce file size – and to validate their work in a layout context (Topic 13) while meeting the AO1‑AO3 requirements of the Cambridge IGCSE ICT syllabus.

1. Theory – Brightness and Contrast

  • Brightness – overall lightness or darkness of an image. Moving the brightness slider to the right adds light; to the left makes the image darker.
  • Contrast – the difference between the lightest and darkest parts. Raising contrast makes details pop; lowering it flattens the image.
  • Brightness and contrast are linked: increasing brightness without raising contrast often produces a “washed‑out” look, while decreasing brightness can hide shadow detail.
  • Histogram tip (AO3): after adjusting brightness/contrast, view the histogram. A balanced image shows data spread across the whole range (left = shadows, right = highlights). If the graph is bunched at one side, adjust the opposite slider or use Levels/Curves for finer control.

2. Software Frequently Used in the Exam

SoftwarePlatformTypical Use in the Syllabus
Microsoft PaintWindowsBasic editing – resize, rotate, reflect, brightness/contrast, simple cropping.
Adobe PhotoshopWindows / macOSFull‑feature editing – all eight operations, layers, groups, resolution & colour‑depth control, file‑size optimisation.
GIMP (GNU Image Manipulation Program)Windows / macOS / LinuxFree alternative with the same feature set as Photoshop; ideal for practice and assessment.

3. Quick‑Reference Table – All Required Image Operations

OperationPaint (steps)Photoshop (steps)GIMP (steps)
Place (insert into a document) Copy → Paste into Word/PowerPoint; use Home → Paste. File → Place Embedded; position with Move Tool. File → Open as Layers; drag layer into layout.
Resize Home → Resize → set % or pixels. Image → Image Size → enter Width/Height or % (maintain aspect ratio). Image → Scale Image → set dimensions.
Crop Select → Rectangular selection → Crop. Crop Tool (C) → drag area → Enter. Tools → Crop → drag → Enter.
Rotate Rotate → 90° CW/CCW or Rotate → Arbitrary. Image → Image Rotation → 90° CW/CCW or Arbitrary. Image → Transform → Rotate → 90°/Custom.
Reflect (flip) Rotate → Flip Horizontal / Flip Vertical. Edit → Transform → Flip Horizontal / Flip Vertical. Image → Transform → Flip Horizontally / Vertically.
Adjust Brightness & Contrast Select → Adjust → Brightness/Contrast. Image → Adjustments → Brightness/Contrast. Colors → Brightness‑Contrast.
Group / Layer Not available – work with separate files. Layers → New → Layer; select layers → Ctrl+G to group. Layers → New Layer; select layers → Ctrl+G to group.
Reduce File Size (resolution & colour depth) File → Save As → JPEG → Quality slider (70‑80 %). File → Export → Save for Web (Legacy) → set Quality, resize, or change Image Size → Resolution and Image → Mode → Indexed Colour. File → Export As → JPEG → Quality slider; Image → Scale Image for resolution; Image → Mode → Indexed for colour depth.

4. Detailed Procedures

4.1 Adjust Brightness & Contrast (including histogram check)

  1. Open the image (File → Open).
  2. If the whole image is to be edited, select it (Ctrl+A).
  3. Open the adjustment dialog:
    • Paint: Select → Adjust → Brightness/Contrast
    • Photoshop: Image → Adjustments → Brightness/Contrast
    • GIMP: Colors → Brightness‑Contrast
  4. Move the Brightness slider:
    • Right → increase lightness.
    • Left → decrease lightness.
  5. Adjust the Contrast slider to restore or enhance detail.
  6. Click the Preview box and observe the histogram (Photoshop: Window → Histogram**; GIMP: **Windows → Dockable Dialogs → Histogram**). Ensure the graph spans the full width – if it is bunched to one side, readjust the sliders.
  7. When satisfied, click OK.
  8. Save a copy (File → Save As) to keep the original untouched.

4.2 Resize an Image (including resolution change)

  1. Open the image.
  2. Choose the resize command:
    • Paint: Home → Resize
    • Photoshop: Image → Image Size
    • GIMP: Image → Scale Image
  3. Enter the new Width and Height in pixels **or** change the Resolution** (PPI/DPI) if the task requires a specific print size. Keep “Maintain aspect ratio” checked.
  4. Confirm with OK and save.

4.3 Crop an Image

  1. Open the image.
  2. Select the cropping tool:
    • Paint: Select → Rectangular selection, then Crop.
    • Photoshop: Crop Tool (C), drag to the desired area.
    • GIMP: Tools → Crop, drag to define the rectangle.
  3. Press Enter** (or click the check‑mark) to apply.
  4. Save the cropped version.

4.4 Rotate and Reflect (Flip)

  1. Open the image.
  2. For rotation:
    • Paint: Rotate → 90° CW/CCW or Rotate → Arbitrary.
    • Photoshop: Image → Image Rotation → 90° CW/CCW or Arbitrary.
    • GIMP: Image → Transform → Rotate → 90°/Custom.
  3. For reflection (flip):
    • Paint: Rotate → Flip Horizontal / Flip Vertical.
    • Photoshop: Edit → Transform → Flip Horizontal / Flip Vertical.
    • GIMP: Image → Transform → Flip Horizontally / Vertically.
  4. Save the rotated/reflected image.

4.5 Group / Layer Management (Photoshop & GIMP)

  1. Open the image as a new layer or create additional layers (File → Open as Layers).
  2. To group layers, select them in the Layers panel and press Ctrl+G (both programs).
  3. Rename the group (e.g., “Background”, “Text”).
  4. Groups let you move, resize, or apply adjustments to several layers at once – essential for complex layouts.
  5. When the final export is required, flatten the image (Layer → Flatten Image) **after** saving the layered source file (.psd or .xcf).

4.6 Reduce File Size – Resolution, Colour Depth & Compression

  1. Open the image.
  2. Change resolution (PPI/DPI) if the specification calls for a particular print size:
    • Photoshop: Image → Image Size → Resolution.
    • GIMP: Image → Print Size → X/Y resolution.
    • Paint: No direct DPI control – resize the pixel dimensions to the required size.
  3. Reduce colour depth (useful for very small web files):
    • Photoshop: Image → Mode → Indexed Colour → choose 256 colours or fewer.
    • GIMP: Image → Mode → Indexed → 256 colours.
    • Paint: Not available – rely on JPEG compression.
  4. Compress the image:
    • Paint: File → Save As → JPEG → Quality slider (70‑80 %).
    • Photoshop: File → Export → Save for Web (Legacy) → set JPEG Quality, optionally resize.
    • GIMP: File → Export As → JPEG → Quality slider.
  5. Check the final file size (right‑click → Properties) and ensure it meets the brief (e.g., ≤ 150 KB).

4.7 Disabling Automatic Colour‑Profile Conversion (to avoid colour shift)

  • Photoshop: Edit → Color Settings → uncheck “Profile Mismatches: Ask When Opening”. When saving, use Save As → Embed Color Profile** = **No**.
  • GIMP: Edit → Preferences → Colour Management → set “Mode of operation” to **No colour management** or deselect “Enable colour management”.

5. Integrating Images into Layouts (Topic 13 – Layout)

  1. Insert the edited image: Insert → Picture** (Word/PowerPoint/Publisher) or the equivalent in the web authoring tool.
  2. Choose a wrap style – the syllabus recognises five:
    • In line with text
    • Square
    • Tight
    • Top and bottom
    • Behind/Front
  3. Set the wrap style via the picture formatting pane (e.g., **Format → Wrap Text** in Word).
  4. Align precisely:
    • Use the alignment buttons (Align Left, Centre, Right) or drag while holding Alt** for pixel‑perfect placement.
    • Group the image with accompanying objects (Ctrl+G) to keep relative positioning.

6. Proofing – Validating Image Edits (Topic 15 – Proofing)

Before finalising any image, perform the following checks (AO3 – evaluation):

  1. Before & After comparison on a neutral grey background – look for over‑exposure, loss of detail, or colour shift.
  2. Zoom to 100 % to verify that edges are clean after cropping or rotation.
  3. File‑size verification – confirm the exported image meets the size limit and that compression artefacts are minimal.
  4. Print test (if required) – print a proof copy to ensure brightness and contrast appear correctly on paper.

7. Mini‑Project – Applying the Full Skill Set (AO2)

Task: Create a one‑page flyer for a school charity event.

  1. Insert a background photograph.
  2. Resize it to fit the page (e.g., 800 × 600 px).
  3. Crop out unwanted borders.
  4. Rotate or reflect the image to achieve the desired composition.
  5. Adjust brightness + 15 and contrast + 10 (or values that achieve readability).
  6. Add a caption in a separate text box; group the caption with the image.
  7. Reduce the final file size to ≤ 200 KB (JPEG, 75 % quality or lower resolution/colour depth as needed).
  8. Save the original editable file (.psd or .xcf) and the final export (.jpeg).

Submit both files and a short reflection (see Section 8).

8. Reflection & Evaluation (AO3)

Answer the following in a brief paragraph (150‑200 words):

  • How does increasing brightness affect the perceived contrast and the file size of the exported image?
  • Which combination of brightness, contrast, and compression gave the best balance for screen display versus printed output?
  • What difficulties did you encounter when grouping layers, and how did you resolve them?

9. Mapping of Assessment Objectives

AOWhat the student must demonstrate
AO1 – KnowledgeRecall terminology (brightness, contrast, DPI, colour depth, wrap style, etc.) and identify the eight required image‑editing operations.
AO2 – ApplicationPerform all eight operations correctly in the chosen software and integrate the edited image into a layout.
AO3 – Analysis/EvaluationExplain the visual impact of brightness/contrast changes, justify file‑size decisions, and evaluate the suitability of the final image for its intended medium (screen vs. print).

10. Common Errors and How to Fix Them

ErrorCauseSolution
Image looks washed outBrightness raised too much without contrast adjustment.Reduce brightness slightly; increase contrast until detail returns. Check the histogram.
Shadows lose detailBrightness lowered excessively.Raise brightness a few points; use Shadows/Highlights (Photoshop) or Levels to recover detail.
Colour shift after savingAutomatic colour‑profile conversion or low‑quality JPEG.Disable colour‑profile embedding (see 4.7) and export with a higher quality setting (≥ 75 %).
File size still too largeResolution or colour depth too high.Resize to required pixel dimensions, lower colour depth (indexed colour), then re‑export with a lower quality slider.
Layer group disappears after exportExported a flattened image without saving the layered source.Save the working file (.psd/.xcf) before flattening; export a separate flattened copy for submission.

11. Assessment Checklist (AO2 & AO3)

  • Can you open an image in Paint, Photoshop, and GIMP?
  • Can you locate and use each of the eight required image‑editing tools?
  • Can you adjust brightness & contrast and explain the visual impact (including histogram interpretation)?
  • Can you resize, crop, rotate, reflect, and group layers correctly?
  • Can you reduce the file size to a specified limit without noticeable quality loss (using resolution, colour depth, and compression)?
  • Can you insert the edited image into a document, choose an appropriate wrap style, and align it precisely?
  • Can you proof the final image by comparing before/after, checking file size, and printing a test copy if required?
  • Can you produce a mini‑project that combines at least four of the operations?
  • Can you evaluate the effect of your adjustments on contrast, file size, and suitability for print vs. screen?

12. Practice Activity

  1. Download the sample image sample‑photo.jpg (provided by the teacher).
  2. Perform the following sequence (save each step with a clear name, e.g., 01‑resized.jpg):
    • Resize to 800 × 600 px.
    • Crop to remove the left‑hand border.
    • Rotate 15° clockwise.
    • Reflect horizontally.
    • Adjust brightness + 15 and contrast + 10 (or values that give a clear, readable image).
    • Group the image layer with a text caption (“Charity Run”).
    • Export as JPEG with a quality setting that results in a file ≤ 150 KB.
  3. Answer the reflection questions in Section 8 and submit both the layered source file and the final JPEG.

13. Summary

Adjusting brightness is one component of the IGCSE image‑editing skill set. Mastery of all eight operations, explicit control of resolution and colour depth, and rigorous proofing ensure that students meet the requirements of Topics 12 & 13 and can demonstrate the analytical abilities required for AO2 and AO3.

Suggested diagram: Screenshot of the Brightness/Contrast dialog in Photoshop showing the Neutral (0), Positive (+), and Negative (‑) positions of each slider, with a small histogram inset.

Create an account or Login to take a Quiz

95 views
0 improvement suggestions

Log in to suggest improvements to this note.