Working with Transparencies

Flattened transparencies and sharpening

Many users tend to think only of photographic images when it comes to sharpening in PDF data. Through flattened transparencies, vectors and text can result in pixel images. These pixel images are treated exactly the same as photos if sharpening is active in ZePrA. This may lead to unwanted artifacts. Differentials in sharpening between neighboring objects (which could be preserved vectors or text), can cause visual dissimilarity. Test the effects prior to production.

When flattening verify the transparencies in ZePrA verify the results. In this case, sharpening is performed prior to color conversion and flattening. Without transparency flattening, ZePrA would apply the sharpening after color conversion.

Depending on what the interplay of elements in the layout program, the parameters for flattening the transparencies and the sharpening parameters in ZePrA look like, extreme sharpening can lead to undesirable visual effects.

transparency-sharpness

The negative effects are revealed only with the most extreme sharpening strength and a threshold of 0. Since JPEG artifacts usually exhibit only very small color differences, a high threshold is the most important criterion for avoiding undesirable effects.

The following example demonstrates the interaction with various levels of sharpness. In this (image)case, the graphic artist has placed an object with shadows over a gradient. In flattening the transparencies, the flattened objects were compressed in the JPEG format. With extreme sharpening, artifacts which are not normally visible are intensified in the part of the gradient that has been changed into a JPEG image through the overlying shadows. From top to bottom, the following sharpness settings were applied:

No sharpening

0.35 points, Amount 80, Threshold 8

0.35 points, Amount 300, Threshold 4

0.35 points, Amount 500, Threshold 0

Converting PDF files with transparencies

ZePrA can be used for the color management of PDF files with transparencies. Choose to preserve transparencies or flatten them via Transparency flattening. The ZePrA approach for color conversion, when preserving transparencies, is that every object – with or without a transparency – are color converted individually, the structure of the PDF document being preserved. There are many variations for the blending of transparencies and the stacking order of semi-transparent objects that there are no rules defined regarding when transparencies should be flattened to avoid unwanted color shifts when converting the colors.

Flattening requires resolution to be specified for platesetters. Whenever possible, avoid flattening until later in the workflow. ColorLogic recommends first converting the colors without flattening the transparencies in ZePrA and examine the results in a transparency compatible PDF viewer (e. g. the latest version of Adobe Acrobat Pro). If artifacts are evident in the file following color conversion, try deactivating the Convert all transparent elements in PDF files checkbox under Configuration/PDF and convert the file again.

flattenting-issues

In many cases, deactivating this option helps to preserve the impression of the original file (see also the example in the middle) (image) because ZePrA excludes certain transparency modes from color conversion. The option should, however, be activated as standard.
If deactivating the Convert all transparent elements in PDF files option does not eliminate artifacts, the next step is to enable Transparency flattening in ZePrA (in the PDF tab).

Note: Transparency flattening is based on the Callas SDK, which in turn uses the Adobe PDF Engine for transparency flattening. The results from ZePrA are the same with current versions of Acrobat Professional and Callas pdfToolbox.

SaveInk and TAC reduction for PDF files with transparencies

Auto Setup queues do not activate transparency flattening as standard with Save Inks or Optimize TAC. In many cases, transparency flattening is not necessary, especially for PDF files with normal transparencies such as drop shadows. However, there are certain situations where transparency effects change the color appearance, despite high quality SaveInk profiles, or where the total area coverage is exceeded despite correct reduction profiles. ColorLogic recommends that following TAC reduction and SaveInk application; examine the total area coverage using a modern preflighting program that takes into account transparencies. If, for performance reasons, you cannot, or do not want to, examine every file, then we recommend that you activate Transparency flattening in the configuration.

Converting spot colors with transparencies

When PDF files, that include process and spot colors, are flattened, the Adobe transparency flattening provides that spot colors are maintained. However, in order to preserve the appearance of the original file, they are set to overprint. Overprint preview should always be enabled when viewing flattened PDF file in the PDF viewer (e.g. Adobe Acrobat Pro). Basic PDF viewers, such as Mac Preview and many apps on tablets, lack overprinting support and display these files incorrectly.

Should ZePrA be used for high-quality conversion of spot colors to the output profile instead of the PDF preflighting program or the RIP, optimally convert spot colors into process colors under Configuration/Convert spot colors. Please note, that due to transparency flattening, converted spot colors may be on overprint and mixed with process colors. This can lead to unwanted results and the “disappearance” of converted spot color objects. If this occurs, use the transparency flattener preset Dissolve overprinting. The most extreme method to would be to rasterize the file completely.

Transparency flattening, image quality and file size

With transparency flattening, ZePrA creates the resulting rasterized objects with lossless ZIP compression. This produces the best results in terms of quality, but also results in a larger file size compared to JPEG compression. Even in the case of PDF files with JPEG-compressed images, transparency flattening results in ZIP-compressed images. If you want to reduce the file size and can accept a drop in quality, then you can switch the configuration of the Compression method to JPEG in the Image quality section of the Options tab.

options-main-1

Note: ZePrA only takes the compression method into account when performing a color conversion. If performing transparency reduction without color conversion, in ZePrA then no compression modification is made and rasterized objects will be ZIP compressed.