Digital Image File Formats, and When to Use Them
Are You Confident That You Know When You Should Use a Specific Type of Image Format? Within Fms Teaching and Research There Is a Great Demand for Clear and...
Are you confident that you know when you should use a specific type of image format?
Within FMS teaching and research there is a great demand for clear and detailed images – this could be for purposes such as sharing diagnostic images or microscope views in high clarity, photographs of real cases and examples, or designing something eye-catching to promote your initiative. The detailed guide below explains the types of image formats you may find useful for different purposes.
There are several image formats that you are likely to come across, but what you may not know is that they can be separated into two ‘families’. This guide will help you understand the characteristics of each format, and which situation lends itself best to each.
Before we go into the details of each specific format, let’s talk about the two key families. These are VECTOR images and RASTER images, and while at certain sizes they could look almost exactly the same, their construction is fundamentally different.
Vector Images
Vector graphics are based on mathematical formulas that define geometric shapes such as polygons, lines, curves, circles and rectangles. Because vector graphics are composed of geometric constructions, they are best used to represent more structured images such as icons, line-art graphics and illustrations with flat uniform colours.
File extensions EPS, AI and SVG are examples of this type and are perfect for creating graphics that require frequent resizing such as logos and icons.
Vector-based images are much more versatile than raster-based images, with their most obvious advantage being that vector images are infinitely scalable. This means that the same image could be printed out the with the same clarity at both advertising billboard and postage stamp size. Another advantage is that as they are images that you create from scratch (as opposed to photographic images) they have a transparent background to them by default. If you need a white or coloured background in your file you can simply add a coloured box under your artwork.
Vectors do have a few limitations, such as not handling effects such as blurs, and poor handling of gradients.
Raster Images
Also known as Bitmap images, Raster images are composed of individually coloured square pixels which build up the complete image. As an example – all photographic images are captured as raster images, with TIF, JPG, PNG, and GIF all being examples of raster image file extensions.
Pixels have a defined proportion based on their resolution (high or low), and when the pixels are stretched to fill space they were not originally intended to fit, they become distorted, resulting in blurry or unclear images. When you resize raster images by scaling up you will be compromising their resolution, as a result, it is important to remember to save raster files at your required dimensions. Once you make a source image smaller than its original size there is no going back – unlike vector images!
A note about ‘Resolution’ and ‘Effective Resolution’
Image resolution for raster images is measured in DPI (dots per inch) and this refers to the density of pixels in an image. Websites display images at 72dpi which is a relatively low resolution. By contrast, images that will be used for printing are required to be no less than 300dpi at the size they will be printed.
You can’t just take an image and scale it up dramatically, as it would stretch out and lose quality, as the dots per inch would effectively have been lowered, i.e. the ‘effective resolution’ would be lower.
Must Read
What is compression and why does it matter?
When you save an image, some files need to be ‘compressed’ to keep file sizes down, as the files themselves would be far too large if this didn’t happen. Some formats are ‘lossy’ and some are ‘lossless’. If image compression is lossy, this means that every time you make an amendment and save, you may lose some quality, sharpness or colour data. The quality of the image decreases in proportion to file size.
Here are details of some of the most common file types you’re likely to encounter:
Elena Rostova holds a Master's degree in Public Health Journalism. She covers groundbreaking medical research, holistic wellness trends, mental health awareness, and nutritional science.
