Digital images are now part of our daily lives. From capturing memories and sharing experiences on websites, blogs and social media, to documentation such as news articles, educational materials, presentations and research papers, whether in your personal life or in the workplace, the chances are you use digital images but how much do you actually know about them?
What are digital images
Digital images are data files which when read by a computer produce an image
onscreen and must be opened and read using a software programme. Some digital images are ‘born digital’ meaning they are created using digital technology, for example a digital camera or a mobile phone. Images originating in non digital format, say books or paper documents, are known as ‘born analog’ and can become ‘digitised’ through scanning technology.
There are two primary types of digital image — raster images and vector images.
Raster images
Raster images consist of a grid of dots known as pixels which is short for picture element. Each pixel in an image is given a colour value and this forms a picture, as such when you zoom in or out on a raster image, you see individual pixels which result in a decrease in picture quality.
Raster images are widely used on the web, in digital photography and for display, where the image is viewed at its intended size. Common raster file formats include JPEG, GIF, PNG and BMP.
Vector images
Vector images (also known as vector graphics) use mathematical formulas to represent images as shapes, lines, and curves. Vectors create an image based on points and their relative positions, enabling vector images to be resized without compromising quality so making them well suited for logos, icons, and other creations that need resizing. Vector graphics are best used for creating diagrams or graphics, as each object is stored using an algorithm to make smooth lines. This means that if you make a change to an object, such as resizing it, the quality of the image doesn’t change.
Unlike raster images, vector graphics are not suited for displaying detailed photographs or images with complex colour gradients but are ideal for designs that require crisp, clean lines that can be easily edited or updated. Common vector file formats include SVG, AI (Adobe Illustrator) and EPS. Vector images are predominantly used where precision and scalability are required.
Image formats
Digital images come in different formats. The most common image formats are detailed below. Not sure what type of format your image is? Right click on your image file, select ‘properties’ and a window will be displayed which includes the image format.
JPEG
JPEG (Joint Photographic Experts Group) images are one of the most well known image file formats. JPEG works well across software and other devices meaning it a good choice for sharing images on social media, by email, on websites and in documents.
The strength of JPEG images are they use compression techniques that significantly reduce file sizes while maintaining good image quality. However, these same compression methods mean some image data is lost during compression, so each time you save a JPEG image there is a decrease in quality and its quality decreases with the file size too.
GIF
GIF (Graphics Interchange Format) files are compatible across various applications and operating systems. They are useful for small graphics on websites and in emails where an image is required to be transparent, for example buttons and banners on websites that need to blend with different backgrounds or if you require an animation.
A weakness of GIFs is they are limited to 256 simultaneous colours, so they won’t achieve photographic quality and today ‘new kids on the block’ such as WebP or APNG (Animated Portable Network Graphics) offer superior quality and compression capabilities for animations or images that require rich colour schemes.
PNG
PNG (Portable Network Graphics) images are considered to be ‘next generation’ GIF files. PNG files have a ‘lossless’ image file format which means they use a form of data compression that reduces file sizes without sacrificing any significant information in the process, so the quality of your images will not be diminished. They support transparency and millions of colours and can also be used to create animations. PNGs are ideal for colorful illustrations and graphics containing lines, text, or solid colour areas such as logos, icons, and designs. You can see examples of PNG images on the ‘What’s the Buzz’ blog posts on this website.
TIFF
TIFF (Tagged Image File Format) is a format used in the publishing and printing industry. The format is capable of accommodating layers and pages in a document, which is ideal for complex graphic designs. It also allows for high quality images with lossless compression options, retaining high photographic quality for scanning and printing.
TIFF is widely used for scanning documents for archival purposes where quality preservation is crucial. It can accommodate high resolution images in colour, grayscale, or black and white formats, making it suitable for scanning documents such as photographs, artwork and text. One drawback of TIFF is that the files can be large, which means they may not be convenient for web usage or sharing via email.
BMP
BMP (Bitmap) is an uncompressed raster file format so is well suited for storing and displaying high quality digital images. A bitmap is a method for storing images using pixels. It is called a bitmap because it is a map of where the bits of information are stored. The information is stored as a sequence of numbers for each pixel’s colour. You don’t need to worry about losing data with BMP files but they generally have larger file sizes than other formats so can be difficult to store.
Other image formats
The most common image formats are detailed above but there are other image formats too such as SVG, WebP, HEIF, RAW and EPS.
A note about PDF documents
PDF (Portable Document Format) is not an image file format but it is worth mentioning here as sometimes it is necessary to convert images into PDFs. You can open PDFs on any device and compress them to smaller file sizes without significantly affecting image quality. And, if you need to share multiple images at once, PDFs are a good option as you can convert your images into a single PDF document with tools such as Adobe Acrobat.
Copyright
Whenever you are using images, always be aware of copyright. Just because an image appears on the internet, doesn’t mean it is free to use. Any image that you right click and save or any piece of work that you download belongs to the person who made it or a third party who owns the copyright. However while most copyright owners want their work to be seen, unless they have expressly given permission for their work to be used, you infringe someone’s copyright by using it without their permission. You can learn more about copyright in the blog post titled ‘The importance of copyright‘ on this website.
Further information and sources
- Adobe: A guide to image file formats and image file types
- Adobe: What is lossless compression
- Adobe: Everything you need to know about image resolution
- BBC Bitesize: How do digital images work
- Canva: Design size guide
- DPC Online: Digital images
- Shutterstock: PNG vs JPG vs PDF – Why image format matters
- Shutterstock: Raster vs. Vector Files
- Shutterstock; What is a pixel
© Humblebee Secretarial and Administration Support. All Rights Reserved.
Humblebee 