Describe the creation and editing of digital images and graphics for multimedia, including raster and vector formats, resolution, colour, compression and file types, and their use in products

What this dot point is asking

Images are the most common media element in multimedia, so NESA expects you to understand how digital images and graphics are created and edited. You need to explain raster and vector formats, resolution and colour, image editing, compression and file types, and how images are used in a product. This knowledge decides whether the images in your Major Project look good and load efficiently, and it is examined in the written paper.

Raster and vector graphics

The first thing to understand about digital images is the two fundamental types:

• Raster (bitmap) images are made of a grid of coloured dots called pixels. They reproduce photographs and complex tonal images well, but because they have a fixed number of pixels, enlarging them makes the pixels visible and the image blocky. Their quality depends on resolution.
• Vector graphics are defined by mathematical descriptions of lines, curves and shapes rather than pixels. They scale to any size with no loss of quality and have small file sizes, which makes them ideal for logos, icons and illustrations, but they are not suited to photographs.

Choosing raster or vector for a given image is a basic and frequently examined decision.

Resolution and pixels

For raster images, resolution is the number of pixels in the image, often described in pixels or dots per unit. Higher resolution means more detail but larger files. Images for screen need lower resolution than images for print. Matching resolution to the use, enough for the screen size without bloating the file, is essential in multimedia where load time and storage matter.

Colour and bit depth

Colour in a digital image depends on the colour model and the bit depth, the number of bits used to describe each pixel's colour. More bits allow more colours and smoother gradation but larger files. Screen multimedia uses the RGB additive model, where colours are made by mixing red, green and blue light. Understanding colour and bit depth explains the trade-off between image quality and file size.

Image editing

Digital images are created and edited in imaging software. Common operations include cropping and resizing, adjusting brightness, contrast and colour, retouching and removing blemishes, combining images with layers, and applying effects and masks. Non-destructive editing with layers lets changes be revised without damaging the original. Editing skill turns raw photographs and graphics into polished elements that fit the product's look.

Compression and file formats

Image files are compressed to reduce their size for storage and fast loading:

• Lossy compression discards some image data to make files much smaller, accepting a quality loss, as in JPEG, which suits photographs.
• Lossless compression reduces size without losing quality, as in PNG, which suits graphics with sharp edges and transparency.
• Vector formats store shapes as instructions, giving tiny files for illustrations.

File format is chosen for the image type, the quality needed and the file size you can afford, balancing appearance against load time.

Using images in multimedia

In a multimedia product, images must look good, fit the interface and load quickly. That means choosing raster for photos and vector for logos and icons, setting the right resolution for the screen, editing images to a consistent style, and compressing them to keep file sizes small. In your folio, justify these choices, because efficient, well-chosen images are part of a usable product.