Optical brighteners are additives that paper manufacturers put into paper in order to help a paper look "whiter." They are also called optical brightening agents (OBA), fluorescent whitening agents (FWA) or sometimes "artificial whiteners."

In order to make paper appear brighter, it is common for most paper manufacturers to add certain chemicals to the paper which can take invisible ultraviolet light and cause it to re-emit in the blue spectrum - or fluoresce - at a point that is just barely within our ability to see. While our eyes see this as a brighter, blue-ish white - a light measuring instrument will only see this as a different form of blue. For this reason, printer profiles made with paper using a lot of optical brighteners can produce images that have a yellow tint to them. The profile is trying to correct for what it sees as too much blue in the paper.

Virtually every paper that has a noticeable bright white appearance has some amount of optical brightener. Examples of paper with OBA in it are common office bond paper, Epson Premium Matte, Luster, Glossy, etc., and most every other brand of commercial inkjet paper. The chemical agents in paper causing this fluorescence will lose their effectiveness over time so that over the course of several years, the apparent brightness of the paper will decrease. It won't be "glowing" with the artificial white that it did when new. This is part of the reason why some people choose to print with "natural" papers.

The OBA value can be calculated as follows:

• Measurement of the paper with M1
• Measurement of the paper with M2
• Difference of the b-value of M2-M1

The OBA values can be interpreted as follows:

• OBA value = 0: no optical brightener
• OBA value = 0-4: Little optical brightener
• OBA value = 4-6: Medium optical brightener
• OBA value > 6: A lot of optical brighteners

The term OCR is short for Optical Character Recognition. OCR is a technology that enables automatic text recognition of letters, words, and numbers in image files. The letters, words, or numbers in the file are captured and converted into editable and searchable text.

The technology behind OCR is based on the principle of pattern recognition. Letters, numbers, and punctuation marks are compared with a database and thus recognized as text or text characters and combined into a word or an entire sentence. In the past, automatic text recognition used its custom fonts, which were quickly and reliably identified by the OCR reader. Modern OCR methods use algorithms and artificial intelligence (AI) for this task.

Modern OCR processes can be divided into five steps:

1. Layout analysis – To make individual characters visible at all, the file must first be converted into a black-and-white image. This optimally highlights the text against its background and allows for identifying layout elements such as headlines, paragraphs, or tables.
2. Segmentation – The next step is to distinguish the individual letters from the graphical elements of the file. This involves identifying each text passage line by line.
3. Character recognition – Pattern recognition is used at this point. Each previously found character is now compared with the database. Features such as height, width, or the general structure of the character help in this process. This is how all characters are converted into letters, words, and numbers.
4. Post-processing – Newer OCR methods also perform a kind of autocorrection. Here, artificial intelligence is used to improve the accuracy of character recognition.
5. Encoding – In the last step, the result is transferred to a new file format so that it can be processed or further edited by the user.

PDF does not have a layer construct, as is the case in graphics applications such as Adobe InDesign, Adobe Illustrator or Adobe Photoshop. Layers are referred to as Optional Content Groups (OCG's) in PDF. As the name suggests, OCGs in PDF were initially designed to make content optionally visible or invisible.  The following table explains the differences between the two:

Table 1: Layers vs. OCG's

Optimized saving is also known as linear storage. Thereby, all incremental attachments are incorporated into the file structure which results into the file being saved in the smallest possible file size.

Figure 1: Comparison of the file structure of a PDF file incremental (left) and linear (right)

The advantage of optimized saving is therefore the smallest possible file size of the document. The disadvantage of optimized saving is the processing time as the process of saving the file takes a little longer than usually.

Output Configuration : If a Production Job has been created, the Output Configuration can be changed according to the requirements of the customer or other desired output results. This is necessary for example if the print must be suddenly produced on another machine, or on another material. The output configuration can be changed using the Output Configuration tab.

The output intent describes the final target device with which the color is reproduced in the PDF document. The Working Color Space is overwritten while being displayed and printed. The output condition is described with an ICC profile. The output intent contains an embedded device profile that defines the Color Space of the target device, for example PSO Coated V3.

Overlap – Describes the additional area needed for gluing individual tiles.

See the following link concerning Overlap Parameters.

Overprinting is basically the object-related setting of overprinting parts. These overprinting parts "mix" with each other. For example, when an object that is colored with pure cyan (100/0/0/0) and another object that is colored with pure yellow (0/0/100/0) are set to overprint, they become green. Overprinting elements that are marked with OPM 0 or OPM 1 can be displayed by the overprint preview of various graphics applications - such as Acrobat Pro, InDesign CC, Illustrator CC or the PDF Editor.

Figure: Left: pure cyan, magenta and yellow that are set to overprint; Right: The same objects but set to Knockout

The two states OPM 0 (also known as standard overprint mode) and OPM 1 (also known as Illustrator overprint mode) should not go unmentioned, especially in connection with overprints:

• OPM 0 - this mode means that 0% of the foreground color in a channel overwrites the background color.
• OPM 1 - this mode means that 1% of the foreground color in a channel overwrites the background color.

This means: when two CMYK elements (defined in DeviceCMYK) are superimposed, the upper object is set to Overprint and OPM is also set to 1, the color of the upper element is always used in printing. This is the case unless a color channel has 0 % - in this case the internal value is used. Only various overprint combinations with images are excluded from this rule.

Figure 3: Left: file without overprint preview; Right: file with activated overprint preview

Explanation regarding the above figure:

All three "K" in the background are a light blue area with the color values 50/0/0/0/0 and a black outline with the color values 0/0/0/0/100. The three "K" in the foreground are set to Illustrator overprint mode (OPM 1) and differ marginally in the Fill Color.

• The left "K" has a 100% magenta area, all other color channels are set to 0% (0/100/0/0).  
• For the middle "K", 1% cyan was added to the area (1/100/0/0).
• For the right-hand "K", 1% cyan and 1% black have been added to the area (1/100/0/1).

Table 2: The result of the calculation of overprinting objects with OPM 1.