4.2 Properties and formats of media files

Image files

Digital images are used in many media products, such as posters, websites, and animations. To use them effectively, you need to understand how they work, what affects their quality, and how to choose the right file format for your project.

What is DPI and PPI?

DPI stands for “dots per inch” and PPI stands for “pixels per inch”. Both are used to describe the resolution of a digital image — in other words, how much detail it contains.

Higher DPI or PPI means more detail and better quality, but also larger file sizes. DPI is mainly used for printing, while PPI is used for digital screens.

For example:

A 300 DPI image is high-quality for printing
A 72 PPI image is usually fine for websites

What are pixel dimensions?

Pixel dimensions describe the width and height of an image in pixels, such as 1920 x 1080. This affects how big the image appears on screen and how clear it is.

If you stretch a low-pixel image to a large size, it will look pixelated or blurry. That’s why higher pixel dimensions are needed for large print materials or full-screen web images.

Raster/bitmap and vector images

There are two main types of digital images:

Raster (bitmap) images

These are made from pixels. When you zoom in, you can see the squares of colour. Raster images are great for detailed photos and textures.

Examples: .jpg, .png, .gif, .bmp
Strengths: Good for detailed images and photos
Limitations: Lose quality when resized; large file sizes at high resolutions

Vector images

These are made from paths and shapes instead of pixels. They don’t lose quality when resized and are perfect for logos, icons and illustrations.

Examples: .svg, .ai, .eps
Strengths: Can be resized without losing quality; small file sizes
Limitations: Not suitable for complex photos or textures

Compressed and uncompressed image files

Uncompressed files

These keep all the original data, so image quality stays high — but the file size is larger.

Example: .bmp, .tiff
Best for: Professional print work, editing where full quality is needed

Compressed files

These reduce the file size by removing data. This makes them faster to upload or download but can affect quality.

Lossy compression – removes some data permanently to shrink the file (e.g. .jpg)
Lossless compression – reduces size without losing any data (e.g. .png)

How to choose the right file format

The format you choose should match how the image will be used. For example:

.jpg – good for photographs on websites
.png – good for transparent backgrounds or logos online
.tiff – high quality for print design
.svg – best for icons and vector graphics on websites

Choosing the right format helps your media product look professional, load quickly, and work well on the chosen platform.