There are many types of digital image type used across the world to store and organise images. Different image types have different qualities and as such used for different applications where one type of image file will work better over another, for varying reasons.
If you’re working with a file that you know will be image heavy, it’s best to try and use an image format that is quite “light”, so the finished document is not overly large (this can especially be problematic if you then want to send it on as some email clients or other programs have file transfer size limits). Even if you do plan to save the document as a PDF, which compresses overall file size, making the image files light will save on overall size.
JPEG files are perhaps the most commonly used type of image file for both sharing online and within document files. They are popular because the degree of compression on the image can be adjusted, so the storage size and image quality can be played around with to get the best solution for the user. The more compressed a JPEG file is, the lower the quality. With this in mind, you can fit a fair amount of JPEG files into a document, but the smaller they are, the worse they will look.
Bitmap files are literally a “map of bits” that make up an image on a digital screen and the file size is increased by how many colours are present in the image. An image only using one or two colours (such as a greyscale image) will be small, whereas an image with many colours will be a lot bigger. The more colours used, the bigger the file size will be – but the quality of the file will be better than a JPEG, for example, due to how a bitmap file represents a digital image. You will still be able to fit a number of Bitmap files into a document with good quality representation but it is largely dependent on the images themselves as to how big they are.
PNG images are classed as “lossless” files and are the most widely used lossless image compression file type on the internet. Lossless files allow the image to retain quality even when compressed, but this does mean they do not compress as small as other file types. This type of file is perfect for documents where quality images are essential (such as a showcase of a graphic designer’s work or a digital photographer) but even when compressed the image sizes won’t decrease to any great degree, leading to a larger file size of the finished document.
BMP files are also lossless and give a large, quality exact representation of the digital image being used. These are typically uncompressed and as such take up a large amount of room in terms of size on a document. It is possible to compress a BMP file without reducing the quality but this is not the purpose of the file type.