Image file formats

There is a simple classification made in respect of graphics software. Raster image files are created in Photoshop, PaintShop Pro and Gimp, while Illustrator, Inkscape and CorelDraw are used to create vector image files.
Raster graphics are used mainly for photographs and graphic designs based on them. Their characteristic feature is the reproduction of an image on a rectangular grid of pixels with predetermined parameters. Any change in the size of the grid results in a change (usually deterioration) of image quality. Zooming-out “squeezes” pixels, while zooming-in “stretches” them on a larger grid.
Raster graphics are most commonly used for websites and web pages. They are usually saved in JPG, PNG, GIF, TIFF and PSD formats.

An example of the raster image.

JPG (Joint Photographic Experts Group) is probably the most popular raster file format, based on compression adjustable on a scale of 1 to 100. It is used to record images and any multi-colour graphics. JPG enables us to store information about the selected colour mode (CMYK/RGB), so it can be used to submit files for printing.

GIF (Graphics Interchange Format) is used to save files limited to 256 colours. It can be used to store static files and animation. Animated files on the web are usually saved in the GIF format.
PNG 8/24 (Portable Network Graphics) is a successor to the GIF format. It enables us to record files in two versions – version 8 using 256 colours, and version 24 using 16 million colours. The “eight” is used when file size is of importance, while the 24 version is used when quality is key. Both versions have the option to preserve transparency.
TIFF (Tagged Image File Format) allows for the inclusion of layers, paths, effects, etc. It is most commonly used to submit flattened versions of graphic designs for printing (billboards, posters). It also gives us the option to include information about the colour mode.
PSD (Photoshop Document) is the default format of a file created in Adobe Photoshop, where the maximum size of the file is 2 GB.

Raster files

Vector graphics are based on curves and shapes recorded using mathematical functions. This feature makes the graphics scalable. This means that vector files can be reduced and enlarged without loss of quality, thus making vector graphics the best solution for designing, for instance, logos, preparing files for printing (conversion of fonts to curves) and displaying them on high-resolution devices. Vector files are usually stored in PDF, SVG, EPS, AI and CDR formats.

An example of the vector image.

PDF (Portable Document Format) – the most common format for submitting text and graphics to the printing house, however it is worth remembering that this format is not a purely vector one – an example of non-vector use of PDF are online scientific publications, rules and regulations and CVs, while a bitmap saved in PDF remains a bitmap. PDFs are suitable for submitting flattened files, as well as those editable in various applications. Files in this format can be opened not only in editors, but also web browsers, which is its undoubted advantage. Many printing houses accept only PDF files.
SVG (Scalable Vector Graphic) is a popular file format for web pages. It enables us to save vector graphics in static and animated forms, using JavaScript, CSS and HTML languages.
EPS (Encapsulated PostScript) is used to save individual pages of graphic files. It is not recommended for submission of editable files, however it gives us the option to do so.
AI (Adobe Illustrator Artwork) is the default format of Adobe Illustrator. It enables us to save vector files with resolutions up to 16383 x 16383 pixels.
In turn, CDR is the default format of CorelDraw. CDR vector files are usually editable, but can’t be opened in all programs.

Vector files

Editable files are files that can be changed freely after opening. It is assumed that editable files are considered to be those in which a design was created. Flattened files are submitted to printing houses in basic formats. However, files saved in the format assigned to the program used to create them do not always have to be editable. Clients sometimes ask for an editable file to edit it in the future. Be careful and steer clear of copyright violations; moreover, in terms of copyright, there is no requirement to consent to the sharing of editable file versions.
Before we proceed to file formatting, let’s find out what technologies and machines are used by the printing house chosen by us. If time is precious and we would like to have the option to introduce changes during the printing process (e.g. customization), we should opt for digital printing, especially in the case of small to medium print runs (even for single copies). Modern digital printing machines provide a quality similar to offset printing, sometimes even surpassing it.