Be able to adjust the brightness of an image

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

3. Quick‑Reference Table – All Required Image Operations

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

10. Common Errors and How to Fix Them

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.