What is digital media? Pixels and colour
Digital media means pictures, sound, video, animation, games and web pages stored as numbers (binary 0s and 1s). Because they are numbers, they can be copied, edited and shared instantly. Social media apps let anyone publish digital media to many people.
A digital photo is a raster (bitmap) image: a grid of pixels (picture elements). Each pixel has one colour.
RGB colour
Screens mix red, green and blue light. Each is stored as a number from 0 to 255 (one byte each, 24-bit colour). R 255, G 0, B 0 is pure red; all 255 is white; all 0 is black. That gives 256 × 256 × 256 ≈ 16.7 million colours. Printers use CMYK inks instead (cyan, magenta, yellow, black).
Resolution is how many pixels an image has, such as 1920 × 1080. More pixels = more detail, but a bigger file.
Raster and vector graphics, digital painting
| Raster (bitmap) | Vector | |
|---|---|---|
| Stores | Colour of every pixel | Shapes as maths: points, lines, curves, fills |
| Zoom in | Gets blocky (pixelated) | Stays sharp at any size |
| Best for | Photos, digital painting | Logos, icons, fonts, diagrams |
| Formats | JPEG, PNG, GIF | SVG, PDF, AI |
Digital painting uses a tablet and stylus with brushes, layers and undo. Layers let you change one part without spoiling the rest. Photo editing tools can crop, adjust brightness and contrast, and retouch, which is also why we must be careful about believing edited images.
Sound, video and animation
Digital sound is made by measuring (sampling) the sound wave many times a second. Music CDs use 44,100 samples per second. More samples and more bits per sample = better quality and bigger files.
Video is a series of still images called frames. Film uses about 24 frames per second (fps); phones often use 30 or 60. Our eyes blend fast frames into smooth motion.
Animation makes frames by drawing (2D), by posing 3D models, or by stop-motion photos. Keyframes mark the main poses; the software fills in the frames between (tweening).
Interactive media (games, websites, installations) changes when the user acts: clicks, touches, moves. A good project is planned, built, tested and improved again and again (iterative design).
File size, compression, copyright and safe work
Image file size (uncompressed) = width × height × bytes per pixel. A 1920 × 1080 image with 3 bytes per pixel = 6,220,800 bytes ≈ 6.2 MB.
Compression makes files smaller. Lossless (PNG, ZIP) keeps every detail. Lossy (JPEG, MP3, MP4) throws away details our eyes and ears hardly notice, so files become much smaller.
Copyright and image rights
- Whoever creates a photo, song or drawing owns its copyright. You need permission to copy or share it, even if it is online.
- Creative Commons licences tell you what is allowed, for example "CC BY" = use it but credit the creator.
- People have rights over their own image: ask before posting a photo of someone.
Working well
Take breaks from the screen (the 20-20-20 rule: every 20 minutes look 20 feet, about 6 m, away for 20 seconds), sit with a straight back, and back up your files. Judge your own work honestly: does it meet the brief? What would you improve next time?
Key formulas and definitions
- Pixel = the smallest dot of colour in a raster image
- Number of pixels = width × height
- Uncompressed image size (bytes) = width × height × bytes per pixel (3 for 24-bit RGB)
- Colours with 24-bit RGB = 256 × 256 × 256 ≈ 16.7 million
- Number of frames = frames per second × seconds
- 1 KB = 1,000 bytes, 1 MB = 1,000,000 bytes (in file sizes we use these rounded SI values)
- Raster = grid of pixels; vector = shapes described by maths
Worked examples
1. An image is 800 × 600 pixels. How many pixels does it have?
800 × 600 = 480,000 pixels.
2. What colour is RGB(255, 255, 0)?
Full red + full green light + no blue = yellow.
3. Find the uncompressed size of a 1000 × 500 image in 24-bit colour.
Pixels = 1000 × 500 = 500,000. Bytes = 500,000 × 3 = 1,500,000 bytes = 1.5 MB.
4. A 10-second animation runs at 24 fps. How many frames must be made?
Frames = 24 × 10 = 240 frames.
5. A school wants a logo for banners, badges and the website. Raster or vector?
Vector. It must be printed huge on banners and tiny on badges, and a vector stays sharp at every size.
6. A 4000 × 3000 photo is 36 MB uncompressed and 3.6 MB as JPEG. What is the compression ratio?
4000 × 3000 × 3 = 36,000,000 bytes = 36 MB. Ratio = 36 ÷ 3.6 = 10, so 10 : 1.
Common mistakes
- Thinking that anything found online is free to use. It is still under copyright unless the licence says otherwise.
- Enlarging a small raster image and expecting it to stay sharp. It becomes pixelated; you cannot add detail that was never captured.
- Forgetting to multiply by 3 bytes per pixel when finding the file size of a colour image.
- Mixing up RGB (light, for screens) and CMYK (ink, for printing).