There are a ton of image formats out there. And since there is so much confusion online about this topic, we thought we’d write a sort of big guide to digital image formats.
So as to avoid problems in sharing a project with our work group, for example, or so as to have a file sent to us in the right format to be able to modify it. Or even to clarify doubts about which extension was most suitable for our project.
In short, an article to simplify your working life. Let’s see together what the main formats of digital images are.
Digital images: two “families” of formats
Digital images are divided first of all into two large families , which correspond to two completely different coding techniques: raster and vector.
Understanding the difference between these two ways in which digital devices process and deliver images is the starting point for understanding how to best use the different formats
Raster images
A raster image, when zoomed in, shows pixels and becomes “grainy”. We talk about raster formats when we are faced with a file made up of pixels , that is, those squares of color placed next to each other in a certain order within a grid of defined dimensions.
The pixels that make up a photograph. This family includes digital image formats widely used in the web environment.
Characteristics of raster images
Precisely because these images are composed of points of color, the way in which we visualize them depends on the magnification and the format. In fact, if we zoom them a lot we can get to see the units that compose them, that is, the pixels. After a certain magnification threshold we obtain a grainy image and if we modify the proportions it will appear stretched or in any case deformed.
Raster formats are suitable or used in these cases:
- In photographs, in general.
- In cases where the images contain, for example, many shades of color.
- In projects where we already know for sure that the image will be used in fixed dimensions , established by us.
- When we need to prioritize a low weight over definition.
In fact, we usually find them used for social content and for images inserted into web pages .
Lossy or lossless
Digital image formats that use the raster technique are then divided into two other categories based on the way in which the information contained in the file is treated.
- Lossless formats (without quality loss) are designed not to lose any of this information; therefore, even if we resize the image, the number of pixels will remain the same, as will the data associated with each of them. It is obvious, therefore, that these are the heaviest formats in this category.
- Lossy formats (with loss of quality), on the contrary, have the characteristic of approximating the image rendering based on the parameters we set, and eliminating pixels not considered useful. The result is a very light file , which however inevitably loses definition.
CMYK or RGB
These are the two different standards with which raster images are created and saved:
- CMYK stands for Cyan, Magenta, Yellow, Black (K): it is the color space that was created for printing . If we talk about color as a material, therefore pigments, these are the four basic colors from which all the others are obtained
- RGB: stands for Red Green Blue. When we talk about color as light (as in the case of all screens) it is from these three colors that all the others are composed.
So for all those files that will be displayed on screen we should prefer the RGB color space, while for those that will be subjected to a printing process we should prefer CMYK.
Vector images
A vector image, when zoomed, does not become “grainy”. The vector format is defined through mathematical equations and is independent of resolution, in fact it can be enlarged infinitely without suffering any loss of quality and definition.
But now let’s look one by one at the main formats used in digital graphics.
Raster images
JPG or JPEG
It is perhaps the most widespread digital image format; for example, it is the standard format in which cameras save shots (when they do not shoot in RAW). It is a lossy format, so it loses quality as the file size decreases.
It’s not possible to save multiple layers in this format, so for example it is not possible to maintain an alpha channel for transparency (as can be done with PNG), or to intervene on the layers once the image has been exported in this format.
It is a very lightweight format and compatible with most software. It loses quality if you do a lot of editing and saving (this is why memes shared and reshared on social media are often so grainy).
Fun fact: There is no difference between “jpg” and “jpeg”. The name of the extension is an acronym for Joint Photographic Experts Group, the team that developed the format; the two variants exist only because years ago Windows systems accepted extensions no longer than 3 letters.
When to use JPEG format?
This format is great for social media, for sending photographic images to print if you are sure you will never need to modify them again, and for sending a quick preview to clients.
TIFF or TIF
The name is an acronym for Tagged Image File Format. It is a lossless format, so it does not lose information and does not flatten the layers; for these characteristics it is used in all those cases in which it is very important to maintain a very high quality.
TIFF files can also be very heavy and for this reason it is better not to use them on the web; among other things they are not always supported.
When to use TIFF format?
This format is perfect when you export images that need to be printed in very high quality and large format.
GIF
Among the many digital image formats, it is one of those that are having the most success on the web, especially in social communication; the name stands for Graphics Interchange Format.
It is mainly used to create short animations and is very versatile, since it also supports transparency. It is a lossless format, but unlike TIFF, it is not suitable for saving high-quality images since it only supports 256 colors.
When exporting to this format you can control several parameters, such as the amount of colors and information that will be saved. In this way you can obtain very light files. Despite being a lossless format, even in GIF files the layers are flattened and it is not possible to edit them separately at a later time.
When to use GIF format?
This requires you to create very light content for the web, even animated or with a transparent background, but you don’t need a high quality image.
PNG
The acronym stands for Portable Network Graphics: it is a lossless image format that supports the alpha channel. This means that you can obtain images with transparency effects like the GIF format, or even more complex, since the transparency can be modulated.
The range of colors available is much wider than in the GIF format, but only in the RGB space. For this reason, and for the difficulty of obtaining a high-quality PNG file without weight becoming an issue, it is not at all a format suitable for printing. On the contrary, it is very useful for the web, even if the JPEG format is lighter.
When to use PNG format?
When you create web images that use complex transparency effects.
WEBP
This is a fairly recent image format. Released in 2010, it was developed by Google to improve the speed of loading images on the web. It uses both lossy and lossless compression methods. Google has also released features that allow the WebP format to support advanced functions such as transparency and animations.
When to use WEBP format?
When you want to insert images or animations into web pages and maintain maximum loading speed and efficiency.
PSD
The name itself, Photoshop Document , indicates that it is a proprietary format. You surely know Photoshop, which in the professional field is the standard software for working on photographic images.
The PSD format is lossless and maintains the stratification of the layers for subsequent modifications; it was created primarily to manage raster images, but can also integrate vector elements in the different levels. Even if this possibility exists, I want to remind you that Photoshop should not be used for vector graphics work such as a logo.
The high level of performance makes the PSD format ideal for preparing an image for printing. However, it is not recommended when the file must be published or transmitted, for example to a client, since to view it you need the software, precisely.
When to use PSD format?
Well, simply when you have to edit a Photoshop file and therefore during the whole photo editing or photomontage process.
RAW
This is the format that contains all the information captured by a digital camera or scanner. It is used to work on images without losing anything from the original shot or scan.
Files with this extension are therefore necessarily very heavy for this reason. But also because, when they are modified with software such as Lightroom or Camera RAW, they maintain both the original data and the various retouching steps.
This is certainly the ideal format for editing very high-quality images and preparing them for publication. However, due to its peculiarities, you cannot use it to export and share your work once completed, but you will have to choose from all the export formats you find in this article the one that best suits your purpose.
We talked about RAW image format, but in reality this definition includes several extensions, depending on the brand of the camera that captures the image. The most common are
- CR2 (Canon)
- CRW (Canon)
- NEF (Nikon)
- ARW (Sony)
- PEF (Pentax)
- and many others (DCR, MRW, ORF, etc)
When to use RAW format?
To work on photographs taken in very high quality without losing information and prepare them for publication.
Vector Image Formats
SVG
One of the most popular vector image formats , starting from the name of the extension which stands for Scalable Vector Graphics.
It is based on the XML language and can be managed by both vector graphics programs and text editors. The possibility of compression allows for very light files, perfect for publishing on the web. It is also widely used to import 2D vector elements into 3D graphics projects.
When to use SVG format?
To publish images on the web that do not lose quality when resized; it is perfect in the responsive field
EPS
The acronym of this extension stands for Encapsulated PostScript. It has all the features of the vector formats we have already discussed; it can also include raster elements and be converted to raster formats, but with a loss of quality of the photographic elements.
It is usually used to insert vector elements into more complex projects, but is not suitable for final export of work for publication. Its most interesting feature is its excellent compatibility with many vector editing software , not only those from Adobe.
When to use EPS format?
When you need to share, import, export vector elements within more complex projects or archive them for later modifications.
One of the most loved and well-known formats, it allows you to view documents containing text and images via any device, browser and operating system. The acronym actually means Portable Document Format.
It is very effective when we need to manage many different elements (vectors, rasters, texts and interactive objects) within the same document and be sure that the project always appears the same. For this reason it is usually the preferred format when exporting a file for printing.
It doesn’t lend itself very well to modifications, so the advice is to use it only for the final export before publishing or to provide a faithful preview to the client.
When to use PDF format?
When you need to export a project that contains several elements to print, publish or share.
TO THE
As with PSD, this is also a proprietary image format. Developed by Adobe, the extension acronym stands for Adobe Illustrator, the standard professional program for working on vector images.
This is therefore the format to favor when we are still in the creation and modification phase of our project, especially if it is a logo.
It can incorporate raster elements, but as with all vector formats, the best results are achieved when we work separately on the raster and vector elements with specialized software, then compose them and export them to formats that best handle both types of images.
When to use AI format?
When we create from scratch or modify vector images using Adobe Illustrator. While for exporting, publishing and sharing it is preferable to choose other formats (eps for other vector software, pdf for previews or printing and png and jpg for images).
Other vector graphics formats
There are many other vector graphics formats. First of all, those related to other graphics software such as .cdr related to Corel Draw or .afdesign from Affinity Designer.
But there are also formats related to CAD design such as .dxf or .dwg that are widely used in many different applications but are still proprietary formats of the AutoCAD software. Or vector graphics formats used for 3D printing such as .3MF which is instead a non-proprietary format and widely used in the sector.
Generally, each software has its own default file format. However, the most used vector graphics formats remain those mentioned in the previous paragraphs.