File formats

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Traditional engraving is based on vector graphics ("plots"). In contrast, digital printing is based on raster graphics (bitmaps). The most important characteristics of these two file types are presented here.

What is a vector graphic?

A vector graphic describes a collection of so-called "graphic primitives": In the two-dimensional case, these are essentially open or closed polygons and curves (2D splines). In the three-dimensional case, these are primarily the surfaces of different geometrical shapes (ellipsoids, cubes, etc. up to solid simulating 3D splines).

A simple example is the image of a circle. At least two pieces of information are required to save it: the coordinates of the center of the circle and the diameter of the circle. In HPGL format there must also be a reference to a specific pen (stroke width, color) or to a particular tool (shape, diameter). Other file formats allow you to include additional information with regard to filling pattern, transparency and color gradient.

Unlike raster graphics, vector graphics are scalable to any size without loss of information, as well as distorted according to specific algorithms.

Common file formats for vector graphics

The following table lists some common file formats for vector graphics and adds comments to the formats used in "Frontplatten Designer".

Extension

Name

Comments

.ai

Adobe Illustrator

 

.cdr

CorelDRAW

 

.dwg

AutoCAD

 

.dxf

Drawing Interchange Format (DXF)

Exchange format for technical drawings. In "Frontplatten Designer" it is used to represent milling elements with a custom contour and as an export format.

.eps

Encapsulated PostScript (EPS)

Page layout language, with which the appearance of an output (e.g. a book page with a picture) is fixed. Preferred format for processing images for digital printing.

.fpd

Front Panel Design (FPD)

Schaeffer AG proprietary format for the optimal convertibility of a front panel design into a production file.

.odg

OpenDocument drawing

 

.plt

Hewlett-Packard Graphics Language (HPGL)

Format for controlling plotters and milling cutters. In "Frontplatten Designer" it is used to represent linear or planar engraving objects with a custom contour.

.ps

PostScript

Page layout language, with which the appearance of a multi-page output (e.g. an illustrated book) is fixed. Preferred format for processing images for digital printing.

.svg

Scalable Vector Graphics

XML-based specification for describing two-dimensional vector graphics recommended by the World Wide Web Consortium (W3C).

What is a raster graphic?

A raster graphic (pixel graphic, bitmap) describes an image as a grid-like arrangement of picture elements (pixels), each of which is assigned a color. For the output (printing, etc.) of a raster graphic, the following specifications must be determined:

Resolution in dpi ("dots per inch") or alternative unit of length (determination of the relationship between the grid dimensions i.e. width and height in pixels, and the absolute length).
Color depth in bits per color channel (RGB, CMYK, etc.) or according to a color table.

The output size of a grid-like arrangement of colored picture elements can indeed be adjusted, but the raster becomes more apparent as the output size increases. This raster can indeed be artificially refined (image processing), but details which were not initially resolved cannot under any circumstances be faithfully reconstructed. Hence the output size of each raster graphic (upwards) is limited.

Common file formats for raster graphics

The following table lists some common file formats for raster graphics and adds comments to the formats which are important for digital printing.

Extension

Name

Comments

.gif

Graphics Interchange Format (GIF)

Unsuitable for photographs because of the limitation in color depth.

.jpg

JPEG File Interchange Format (JFIF)

Lossy compression of raw data, suitable for photo-like images, not for text and hard color transitions.

.jp2

JPEG 2000

Good compression of raw data, suitable to a limited extent for different images.

.png

Portable Network Graphics (PNG)

Generally recommended format for lossless compression of images.

.psd

Photoshop Document

Lossless processing of raw data. Adobe Photoshop format which many other programs can also read and write.

.psp

Corel Paint Shop Pro

Lossless processing of raw data. Corel Paint Shop Pro format.

.raw

RAW Graphics Format / raw data format

 

.tif

Tagged Image File Format (TIFF)

Lossless, versatile processing of raw data.

Comparison between vector and raster graphics

Vector and raster graphics both describe images in computer readable form. They differ in how they abstract the figure that is to be reproduced:

A raster graphic describes an image as a grid-like arrangement of picture elements (pixels), each of which is assigned a color.
A vector graphic describes an image as a collection of so-called "graphic primitives" (2D: lines, ellipsoids, polygons, and curves), which in addition to their geometry, may be assigned other properties such as color or line thickness.

The strength of a raster graphic is that, with the appropriate resolution and color depth, every (two-dimensional) figure can in principle be faithfully reproduced. This is in turn of course linked to a corresponding file size.

The strength of the vector graphic on the other hand, is that it can present an array of graphic elements in any desired output size, whereby these elements may be assigned other characteristics (tools, filling pattern, transparency, color gradient, etc.).

Thus the strength of the one format is basically also the weakness of the other.