File Processing Options
Black Point Compensation
If PDF preflight software or a workflow option does not offer the option of converting RGB to CMYK with black point compensation, or of using DeviceLink Profiles, allow it to process in ZePrA.
Ignore PDF Rendering Intent
Selecting Configurations / Options -Ignore PDF Rendering Intents prevents the rendering intent of the PDF file from being read, giving the priority to the rendering intents preset in ZePrA under Images and Vectors. Note that in this situation, the setting is no longer compliant with PDF/X rules.
Compression Methods: Three Compression Methods can be specified for image color conversion.
Automatic setting to ensure all image formats are preserved. JPEG compression causes TIFF and PSD files, as well as ZIP data contained in the PDF file to be converted to JPEG.
In the default setting Automatic, ZePrA does not alter the color depth or the type and compression of the input data. The default setting can be changed to Downscale Images. Enter the required resolution in the Downscale Images line as the dpi value. Use Threshold to specify the resolution form which downscaling should be performed, e.g. for the web or a desired resolution for printing. Using Threshold gives the user the ability to prevent unnecessary resizing. To compensate for the lack of sharpness that can result from downsampling images, the Catcall bicubic interpolation method is used in the background.
Lossless: saves the format of the image file in either the PSD or TIFF format. JPEG data compressed in PDF files are converted to ZIP. Multicolor files cannot be saved as JPEG.
Choose from four predefined quality levels of the selected configuration via JPEG Quality. Percentages can also be set under the Custom setting. The quality of compression of
JPEG: pixel images and of JPEG compressed images in PDF files can be influenced via JPEG Quality. The compression rate is set to high quality by default in ZePrA which results in larger file sizes after color conversion of highly compressed JPEG images.
Tip: ColorLogic recommends using the default setting High 90%
The Calculate Ink Savings option calculates the overall amount of CMYK ink saved when applying SaveInk profiles to each individual file. Ink savings calculation can be selected via Calculate Ink Savings or they are automatically activated with the SaveInk queue created using the Auto Setup wizard. The savings in percent are indicated in the Processed Jobs table in the Overview window and in the Job Properties window. The ink savings are displayed separately for each calculated file. To view the Job Properties, right click on a file in the main Overview/Processed Jobs window and select Show Job Properties.
A SaveInk Report can be generated via the Tools menu. This report generates a detailed overview of each SaveInk queue that’s been set up and the jobs that were processed. The overview lists the overall ink savings across all queues, the savings per queue and the savings per job which can be beneficial when calculating costs. The reports can be created as PDF, TXT, HTML or XML files.
Vector Graphics and Text
Text and vector graphics are independent objects within the PDF format. For both types of objects, the ZePrA options offer possibilities for preventing black vector graphics or black text form being composed of four colors as a result of iCC conversion. These options are not necessary when using ColorLogic DeviceLink profiles since the profiles are calculated so that the pure black always remains pure.
Preserve Black and Gray for Vector Graphics
Converts RGB black to pure CMYK black. This option also ensures that shades of gray created as vectors are preserved. A 50% K shade will remain unchanged at 50% K. A medium gray RGB shade with RGB=128/128/128 will be set to 50% K after CMYK conversion.
Leave Text Elements Unchanged
ZePrA differentiates between vectors and text. If only vector graphics need to be converted and not the text, activate the option.
Lack of sharpness of an image during capture are typically fixed in the camera or the image capture software. Sharpening as a creative option is sometimes used in combination in image processing.
For sharpening images after color conversion, use Sharpening feature under Options. In media production, there are several reasons for performing sharpening:
- To compensate for inadequacies of digitizing (digital photo or scan)
- Sharpening as a creative option
- Compensating for loss of detail after changing the image resolution
- Compensating for inadequacies of printing processes (e.g. screening)
Compensating for loss of detail after changing the image resolution and compensating for inadequacies of printing processes can both be executed in ZePrA. Apply sharpening of the image data to individual color formats (CMYK, RGB, Multicolor, Gray, LAB) or to all color formats simultaneously.
ZePrA generally performs sharpening after color conversion. In certain situations, if transparency reduction is to be performed simultaneously, by enabling Transparency Reduction in ZePrA, images are sharpened before color conversion.
Tip: The interpolation method bicubic (sharpener) found in Photoshop does produce sharper images than ZePrA, but shows considerable artifacts unlike ZePrA. With ZePrA, downscaling and resharpening can be combined, as described in the Sharpening section.
Depending on the task, images may be sharpened according to color space or only images scaled in ZePrA may be sharpened.
Moderate sharpening of all images: Compensating for normal anomalies in the printing process
Strong sharpening of RGB and Gray images: for media neutral workflows that involve working with high-resolution RGB and Gray master images.
Moderate sharpening of downscaled images: Compensate for slight loss of sharpness due to downscaling.
Custom sharpening: Details on custom sharpening below
Tip: Using caution when using sharpening in ZePrA for PDF files from various sources versus files created in a controlled in-house workflow. Setting the Amount to 80% and the Threshold to 8 will usually delivers stability. Recommended Preset: Moderate Sharpening of all Images.
The Preset Custom defines all sharpening parameters. ZePrA uses the sharpness algorithm “unsharp masking” which are found in Photoshop. Image sharpening involves intensifying the differences in brightness or color between two adjacent pixels, resulting in strong sharpening that can create lines between the image areas with differences brightness/color.
The option has three settings:
Radius: The bigger the radius, the wider the line produced during sharpening. Selecting the correct radius depends on numerous parameters such as the normal viewing distance or the resolution of the printing process used. Read more (link) under Correlation Between Scaling and Image Resolution.
Amount: Defines the intensity of the sharpening based on the chosen radius. The Amount should be set based on the sharpness of the original image(s) and the anomalies in the printing process.
Threshold: The threshold is the difference in color or brightness starting from which the sharpness filter is applied. The lower the threshold is set, the more image areas will be included in the sharpening and the larger risk of unwanted image artifacts. The normal values range from 2 to 10.
Tip: Excessive sharpening due to a high Radius setting and an high value can result in an unnatural looking image. Depending on the sharpness settings, artifacts that were not previously visible may become visible and overemphasized, which can be seen in the square pattern of a JPEG compression or in image noise in dark areas of digital photos. Read more (link) Special Workflow Options / Flattened Transparencies and Sharpening.
Image Based vs Output Based Sharpening Radius
ZePrA offers two options for defining sharpening radius; image based and output based sharpening. In image based sharpening, the radius is given in image pixels. If a radius of 2 pixels is entered, the effective width of the sharpness effect will be 2 pixels wide. This corresponds Unsharp Masking the methodology in Photoshop. If a sharpened image is put in a layout program, the visually perceived effective width of the sharpening radius depends on the image resolution in pixels per inch and how much the image has been scaled in a layout program.
Example: If an image with a 288 ppi resolution and a sharpness radius of 2 pixels entered ZePrA with 100% scaling in the layout program, then the visually perceived sharpening radius is 0.5 points (0.18mm). 72 points = one inch. For an image with 288 pixels per inch, one pixel is 0.25 points wide.
Output based sharpening: the sharpness radius remains the same in points or in mm for images at different resolutions or sizes within a layout program. Output based sharpening primarily compensates for loss of detail in the output system and it ensures that the sharpening radius for all images in the document similarly counteracts the loss of the detail of the output.
Correlations Between Scaling and Image Resolution
Reducing the image of the example above with 288 ppi in the layout program to 50%, then the image resolution changes to 576 ppi. With regard to the image pixel, output based sharpening with 0.5 points results in a doubled radius of 4 pixels. Typical image based sharpness radii in 300 dpi images with 100% scaling in the layout program correspond to the following data for output based sharpening in points:
0.8 pixels = 0.19 points:
0.9 pixels = 0.22 points
1.0 pixels = 0.24 points
1.1 pixels = 0.26 points
1.2 pixels = 0.29 points
1.3 pixels = 0.31 points
1.4 pixels = 0.34 points
1.5 pixels = 0.36 points
1.6 pixels = 0.38 points
Convert the width of an image pixel with any resolution into points using this formula:
Radius in points = 72 / image resolution in ppi
Instead of ppi, Adobe Photoshop uses dpi. Relating the sharpening radius to the screen ruling used for printing, the sharpness radius should not be greater than the screen ruling. Use the following table which shows the screen ruling and the sharpness radius in mm in the ratio 1:1
60 l/cm= 0.17 mm (0.48 points)
70 l/cm = 0.14 mm (0.40 points)
80 l/cm = 0.13 mm (0.37 points)
90 l/cm = 0.11 mm (0.31 points)
100 l/cm = 0.10 mm (0.28 points)
110 l/cm = 0.09 mm (0.26 points)
120 l/cm = 0.08 mm (0.23 points)
200 l/cm = 0.05 mm (0.14 points)
Printing with a screen ruling of 70 l/cm means the radius should be 0.14 mm or smaller. To calculate a sharpness radius in mm, corresponding to a given screen ruling, use the following formula:
Radius in mm = 10 / screen ruling in lines per centimeter
Sharpening and Image Resolution in Relation to Viewing Distance, Printing Process and Screen Ruling
One method to determine the sharpening radius is to base it on the viewing distance, the printing process and the screen ruling used for printing. The most the eye can see is approximately 0.2mm and 127 pixels per inch for viewing distance of 1m or approximately 0.05mm and 508 pixels per inch for a viewing distance of 25 cm, depending on contrast of structures and position in the field view. The image resolution and the effective width / sharpening radius should only be adjusted to this print resolution if the printing process chosen for the job is capable of reproducing details in the resolution of the eye and the respective viewing distance. It is recommended to have cushion of 1.5 times the print resolution or the presumed viewing distance.
Example 1: For offset printing with a screen ruling of 70 l/cm (178 lpi), details down to 0.14 mm wide can be accurately reproduced, which also defines the maximum sharpening radius. With the 1.5 times reserve, the image resolution should be at least 267 ppi.
Example 2: For an exhibition stand that will be viewed from a distance of 1m, normal eyesight can pickup details down to approximately 0.2 mm, which can be used to determine the sharpening radius. With a 1.5 times reserve, an image resolution of 191 ppi is sufficient here.