OCR J277 - Images (Bitmap) Revision Tool

1 [3 Marks Total]

Images are stored as bitmaps.

(a) Define the term 'pixel'. [1] (b) State what is meant by 'image resolution'. [1] (c) Define the term 'colour depth'. [1]

✅ Mark Scheme

(a) Pixel: Smallest addressable element / single point of colour.

(b) Resolution: Width x Height / Number of pixels in the image.

(c) Colour Depth: Number of bits stored per pixel.

Score yourself (Max 3):

2 [3 Marks Total]

An image has a resolution of 100 x 100 pixels and a colour depth of 2 bits.

(a) Calculate the file size in bits. Show working. [2]

(b) State the maximum number of different colours that can be represented. [1]

✅ Mark Scheme

(a) File Size: 20,000 bits.

(Working: 100 x 100 x 2 = 20,000)

(b) Colours: 4 (2^2 = 4).

Score yourself (Max 3):

3 [4 Marks Total]

A designer increases the colour depth from 8-bit to 24-bit.

(a) Explain the effect on file size. [2] (b) Explain the effect on quality. [2]

✅ Mark Scheme

(a) File Size: It will increase (1) because more bits are used per pixel (1).

(b) Quality: More realistic/better colour accuracy (1) because more colours are available (1).

⚠️ Common Mistake Do NOT say the image becomes "clearer" or "higher resolution". Changing colour depth affects colours, not sharpness.

Score yourself (Max 4):

4 [4 Marks Total]

Files store 'Metadata' along with pixel data.

(a) State two items of metadata. [2] (b) Explain why metadata is needed. [2]

✅ Mark Scheme

(a) Items: Width, Height, Colour Depth, Resolution, GPS, Date.

(b) Reason: Tells the computer how to reconstruct/display the image (e.g., when to start a new line).

Score yourself (Max 4):

5 [1 Mark]

A file is 3,000,000 bytes. Calculate the size in Megabytes (MB).

✅ Mark Scheme

Answer: 3 MB

(3,000,000 / 1,000,000).

Score yourself (Max 1):

6 [3 Marks]

Explain why a 10-megapixel image looks better than a 2-megapixel image on a large poster. Refer to pixels.

✅ Mark Scheme

Score yourself (Max 3):