"Overprint" tab

The parameters in this group allow you to control the overprint behavior of the Prinect color manage­ment.

The "Overprint" function is mostly used to avoid register problems and flashes in black fonts and other black graphic objects that lie on top of a colored background. For design purposes, overprint is also used with hard shadows or colored CMYK objects. You can control overprint best if it is set directly in the application that creates the job.

The overprint settings of the Prinect Color Management on the one hand compensates for application shortcomings and on the other processes faulty documents so that you get the overprint effect you want. It's not possible to detect on a print side which object is to overprint in the Prinect workflow and which not. You can use the Prinect PDF Toolbox for the interactive correction of single objects.

Another problem is that different applications, different RIPs and different users have different ideas about which objects on a page will overprint.

In older versions of the Adobe PostScript interpreter, only spot color objects could overprint following the PostScript Specification that was then applicable. Objects that were created in the "device" color spaces (gray, RGB, CMYK) couldn't overprint. Such objects were always knocked out in a pure CMYK output.

More recent versions of the Adobe PostScript interpreter, such as is found in the current version of the Prinect Manager software, use an additional, new overprint mode. The CMYK Overprint Mode determines how DeviceCMYK objects with the "Overprint" option enabled behave when they are printed on top of process color elements. The overprint mode affects only color channels set to 0% ink coverage.

CMYK vector graphic or font objects (not images) where the color data in some channels is zero can overprint background colors if this new overprint mode is used. The new overprint mode is referred to as "Overprint Mode 1" to distinguish it from the previous PostScript overprint mode called "Over­print Mode 0". In Adobe Acrobat Distiller as of version 5, Overprint Mode 1 is known as "Illustrator Overprint Mode". Adobe refers to this functionality as "Nonzero Overprinting".

Example: A CMYK rectangle with the data 100/0/0/0 would only manipulate the cyan separation if the object is set to overprint and "Overprint Mode 1" (OPM 1) is enabled.

If a white object where all the color data is zero is output, Overprint Mode 1 causes this object to dis­appear in the output. However, this only happens if the white object was set to overprint when cre­ated. This problem can be solved with the overprint parameters in the Prinect Color Management.

As of Adobe Acrobat version 5 (not Adobe Reader!), PDF documents that have CMYK objects with Overprint Mode 1 enabled can be displayed correctly. You must enable this option explicitly. RIPs that use the current Adobe PostScript Interpreter can also process such PDF documents correctly.

The "Overprint" parameters in the Prinect Color Management allow you to use Overprint Mode 1 also on older PDF documents where Overprint Mode 1 is not explicitly defined or enabled.

Note: Often applications may output objects differently to the way they were created by their user. For example, an object that was created as a black, overprinting CMYK object could be output by the application as an overprinting, black spot color. If your output is not what you expect or if there are output differences in apparently identical jobs from different applications, then the reason is often PostScript -> PDF or. PDF -> PostScript conversions.

•Definition: "Black objects"

"Black objects" are by default objects that have an area coverage of 100% in black unless a dif­ferent threshold is set in the "Set Black to Overprint if Above or Equal" option. This applies to objects in the following color spaces: DeviceGray, DeviceRGB, DeviceCMYK, Separation (Black) and a single or multi-channel DeviceN where in effect only the channel named "Black" prints (other channels whose color data are zero and channels named "None" are recognized as non-printing). CMYK objects where the data for cyan, magenta and yellow are not all zero are not considered black. Objects in the device-independent color spaces CIEBasedA/-ABC/-DEFG are also recognized if corresponding values can be applied in one of the device color spaces Device­Gray/-RGB/-CMYK. For example, a L*a*b* value of 0/0/0 would not be recognized as black, on the other hand, an sRGB value of 0/0/0 would be. This is because in some color spaces the Color Conversion engine cannot recognize what color values are considered "black". There may be unusual color spaces where this applies, for example, with values of 100/0/0.)

•Definition: "White objects"

"White objects" are those that are created fully white. In other words, there is no threshold as is possible with black objects. White objects can be detected in gray, RGB, CMYK and spot colors. Technically, we are talking about the color spaces DeviceGray, DeviceRGB, DeviceCMYK, Sepa­ration and DeviceN. Separation and DeviceN require that the objects are created so that no ink is applied to paper with them. The color channel(s) must have a value of zero or be named "None".

Grayscale images in DeviceGray and smooth shadings in DeviceGray or DeviceCMYK with an empty C, M and Y channel are not viewed as black or white objects because they can have all grayscales from white to black. It would be wrong to set a light gray shading to overprint if you selected an option with which "black objects" are to be overprinted. It would be too time-con­suming to try and recognize whether an image or a shade only has dark grayscales correspond­ing to 98 - 100% black.

Nevertheless, grayscale images and smooth shadings are manipulated by the Overprint function­ality of Color Management, for example, when it can be seen that they were created incorrectly by an application. In all other cases, they are excluded from being categorized as "black", "white" or "all other" objects and are reproduced as created in the job.

The following options are available:

"Set Colors (save gray and black) to Knockout" option

All overprinting, color elements are set to knockout so they cover elements lying underneath.

You can use this parameter to correct a wrong application of the "Overprint" property in the docu­ments.

You should not enable this option if the page content must be set to overprint, for example, if an over­printing spot color is to produce a color mix.

The overprint status of the color elements remains unchanged if this option is not checked.

"Set Gray and Black to Knockout" option

All overprinting gray and black elements are set to knockout so they cover elements lying underneath.

You can use this parameter to correct a wrong application of the "Overprint" property in the docu­ments.

You should not enable this option if the page content must be set to overprint, for example, if an over­printing spot color is to produce a color mix.

The overprint status of the gray and black elements remains unchanged if this option is not checked.

"Set CMYK White to Knockout" option

If CMYK white (C=M=Y=K=0%) elements are defined as overprinting in a document, they are set to knockout when you check this option.

Elements in overprinting CMYK white on a colored background would not be seen during printing. For example, white text on a colored background would disappear. The "knockout" property makes these CMYK white elements visible in printing. By default, this option is enabled as this is generally what you want.

"Set Black to Overprint if Above or Equal" option

All black elements (graphics, text) defined as knockout that have an area coverage above the set threshold are set to "overprint" if this option is enabled.

This option affects the following color spaces: "DeviceCMYK" with C=M=Y=0%, "DeviceGray" or "/Separation/Black".

"Turn Overprint Device Gray into K" option

All overprinting colors in the "DeviceGray" color space are converted to black if this option is enabled. An additional spot color "black" with C=M=Y=0 (/Separation/Black) is produced. CMY elements (also blends and images) are overprinted by the "black" spot color.

In keeping with the PDF specification, "DeviceGray" colors overprint all spot colors lying lower down. However, contrary to expectations, CMY separations are knocked out. In contrast to this, however, a "black" spot color overprints CMY separations and other spot colors.

Overprinting "DeviceGray" images and shades are generally used for transparent shadows. You would not get satisfactory results if this option is not checked.

All overprinting "DeviceGray" elements in the document remain unchanged if the option is not acti­vated.

"Insert White Mask Box" option

Case of use: In a CAD file, there is a crop line that can be seen as a white line if a solid tint ink pickup mark of the same color as the background color of the PDF page is positioned on the empty areas. The critical aspect about this is that this line can also be seen when imaged to the plate.

Enable this option to avoid this effect. Then a 0% white knockout box the size of the media box is inserted below all content objects. This white box covers the solid tint ink pickup mark in output and as a result white crop lines can no longer be seen.

"Retain CMYK Overprint Mode unchanged" option

Prerequisite: This option can only make an impact if overprint is not disabled by another setting (e.g. by switching to "knockout").

The CMYK Overprint Mode as defined in the PDF document is retained unchanged.

"Enable CMYK Overprint Mode (OPM=1), unless otherwise specified" option

When a CMYK Overprint Mode is missing from the PDF document, "Overprint Mode (OPM) 1" is enabled. In other words, 0% CMYK graphics or text is set to overprint. A CMYK Overprint Mode that is defined in the document is used.

"Always enable CMYK Overprint Mode (OPM=1)" option

The "Overprint Mode (OPM) 1" (0% CMYK graphics or text is set to overprint) is always enabled, irre­spective of whether a CMYK Overprint Mode is enabled in the document or not..

"Always disable CMYK Overprint Mode (OPM=0)" option

The "Overprint Mode (OPM) 0" (no overprint with 0% CMYK graphics or text) is always enabled, irre­spective of whether a CMYK Overprint Mode is enabled in the document or not.

Note: You will find information about Overprint Mode 0 or 1 in the "Overprint" tab.

An example of how the Overprint Mode (OPM) reacts in overprint now follows:

Behavior of OPM with overprint