Registration Marks [1], also known as the register cross or register, is a graphic figure that can be used to monitor the accuracy of fit of the individual colours in the printing process. Usually this mark consists of a circle and a cross of thin lines, similar to a target cross. By precisely aligning the individual separations, "flashes" in the printed image can be avoided.

For the register mark to be printed on all separations (CMYK + Spot Colors), it must be marked with the Registration Mark Color.

Illustration: A visual representation of the positioning of Registration Marks on the printed image

A Registration Mark Color is a color definition that is printed at 100% in each separation. Thus, a surface which has been marked with this color has 400% total ink coverage in a CMYK print. With a CMYKcm-OVG print, the total ink coverage would already be 900%.

Technically, there is a color definition called "All" for the registration mark color in PDF and PostScript.

The Registration Mark Color should be used in design creation only for Registration Marks or Crop Marks and not for creating deep black vector areas or texts.

Method for converting different color spaces from one space to another.

Number of identical copies of a motif or a page of a motif.

In relation to a single printed sheet, this is the number of copies to be cut from this sheet.

RGB is one of the physical-technical color models that describe a color as a mixture of primary colors. As the human eye contains three types of color-sensitive cones, the triple theory was developed early. This theory has remained the basis of color television on monitors and color photography to this day.

The triple theory states that all visible colors are mixed together from exactly three primary colors. The condition for the primary color criterion is that none of the primary colors can be mixed from the other two.

Figure 1: Schematic depiction of the primary and secondary colors in the RGB color space

The additive color model RGB is based on the primary colors red, green and blue. If all primary colors are mixed, the color "white" is created. Where only two of the three colors are mixed, the so-called secondary color is created. In RGB, the secondary colors are Cyan, Magenta and Yellow.

Secondary colors are also referred to as the complementary color of the missing third primary color. The mixture of Green and Blue results in Cyan. Cyan is therefore the complementary color to the missing Red. This results in characteristic pairs of complementary colors:

• Red > Cyan
• Green > Magenta
• Blue > Yellow

A RIP - Raster Image Processor is a special software or a combination of hardware and software that converts data from a page description language such as PostScript, PDF or PCL into a pixel graphic (raster graphic), which is then usually output to a printer.

A RIP essentially implements two functions:

1. Rendering – conversion of vector graphics into pixel graphics (raster graphics) into a halftone image in a certain resolution
2. Screening – conversion of the halftone image into a pixel image consisting only of the existing print dots

The term Raster Image Processor is only used explicitly in prepress, where this component performs other tasks in addition to the functions mentioned above:

• Color management – Calculation of colors in the output color space
• Separations – create individual color separations for the printer
• Grid – Create a pixel grid, where pixels are either distributed or arranged at an angle.
• Trapping – create additional areas to avoid speed cameras at hard color edges

Run Length Encoding (RLE) is a very simple compression algorithm that is supported by many pixel file formats such as TIFF, BMP, PCX, Targa and, of course, PDF. In general, the method is suitable for all types of data, regardless of their information content. However, the degree of compression is strongly determined by the information content, which makes a thorough knowledge of the processes of this algorithm absolutely essential. Under unfavorable circumstances, it can happen that the result of the compression is a larger file than the original.

RLE is based on the reduction of the physical size of repetitive information (redundancies). The sequence of information with the same content is referred to as a Run. For coding, information is summarized in a Run Packet , which is usually coded with two bytes, whereby the first byte indicates the number of information in the "Run" (Run Count), the second byte the information value (Run Value). The Run Count can assume values from 0 to 255 or 1 to 256, whereby the value 0 is used in some procedures to separate the Runs. If the series contains more than 255 identical pieces of information, a new Run must be started and a new Run Packet created.

Classical procedure: The character string "aaaabbc" requires 7 bytes when uncompressed (if we assume one byte per character) and only 6 bytes after RLE coding "4a2b1c". From this representation, it can be explained that the type of compression also has limits. Long sequences (Runs) of the same information values lead to a high degree of compression; with constantly changing information, the effectiveness is reduced, which can even double the memory requirement for compressed images. The character string "abc" would be "1a1b1c" after compression, which would double the storage space from 3 bytes to 6 bytes.

Improved procedure: Various forms have been developed to prevent duplication from occurring:

• A counter is included in the Run Count, which indicates the number of uncoded data or indicates that repetitions occur in the sequence.
• Between the Run Packets, if more than three repetitions occur, control characters are introduced to separate the packets.

Summary:

RLE (Run Length Encoding) – ist eine einfache und schnelle Methode der Komprimierung – sie ist Grundlage für viele andere Verfahren. Die Effektivität ist jedoch stark vom Informationsgehalt der Datei abhängig. Ein Schwarz-Weiß-Bild eignet sich sehr gut für RLE, da darin viele Abfolgen gleicher Pixelwerte enthalten sind. Farbbilder hingegen, bei denen jeder Pixelwert einen anderen Wert haben kann, eignen sich nur sehr schlecht für diese Art der Codierung. Die einzige Ausnahme dabei sind Farbbilder, die im indi­zierten Farbraum vorliegen. RLE wird in den verschiedenen Programmen unterschiedlich bezeichnet, z. B. als Run Length oder Lauflänge.

Technisch gesehen zählt RLE zu den verlustfreien, symme­tri­schen Kompressionsmethoden, wobei die Kompression physi­ka­lisch erfolgt. In PDF wird diese Kompression durch den RunLengthDecode-Filter angesprochen. Eine Parametrierung des Algorithmus ist in den Grafik-, Layout und PDF-Editoren nicht vorgesehen.