File Processing Options
Black Point Compensation: To make sure that high-quality color conversion is performed without detail losses in the shadows when using the relative colorimetric rendering intent, Black Point Compensation under Configurations/Options is enabled by default. This is especially important in PDF documents as relative colorimetric with black point compensation is not supported in PDF files before PDF 2.0. PDF 2.0 and higher does support black point compensation – see section below.
Typically the rendering intent to be used when converting or viewing PDF files is defined together with the embedded ICC profile of each object and is set by the PDF authoring application. In such applications, the default rendering intent is usually set to relative colorimetric with black point compensation but in older PDF files – due to the lack of support – this becomes relative colorimetric (without black point compensation) leading to detail losses in the shadows after conversion. For that reason black point compensation is a separate option in the preferences of many PDF applications.
Tip: If you would like to color convert images or PDF documents for proofing using the relative colorimetric rendering intent (for example because you are using the same paper stock for production and proofing) then disable the Black Point Compensation checkbox.
Note: If the Black Point Compensation checkbox is disabled, all color conversions done with the relative colorimetric rendering do not apply black point compensation which may result in plugging of shadows. To avoid this when converting from Document to Target Color Space please use SmartLink in combination with Black Point Compensation.
Black Point Compensation with PDF 2.0 files
Modern PDF 2.0 files support black point compensation in combination with the relative colorimetric rendering intent. Black point compensation in PDF 2.0 can have three states: On, Off, Default. Default means that application specific settings are used, e.g. whatever is defined in ZePrA.
- If the Black Point Compensation checkbox is enabled for the processing of a PDF 2.0 file, black point compensation will be applied to all objects of the PDF (such as images, vectors, text, shadings) with relative colorimetric rendering for the states on and default. Black point compensation will not be used for objects with the state off.
- However, if both checkboxes Ignore PDF Rendering Intents and Black Point Compensation are enabled then black point compensation will always be used.
Ignore PDF Rendering Intent: Activating the checkbox Apply embedded profiles/intents in the Images/Vectors tab considers the embedded ICC device profile as well as the rendering intent embedded in the PDF file. If Ignore PDF Rendering Intents is disabled, which is the default setting in ZePrA, the rendering intents defined in each PDF document for each object are used while those defined in the Images/Vectors tab are ignored. This option only applies to PDF files. For image files (PSD, JPEG, TIFF), the rendering intents defined in the Images/Vectors tab are always used.
Enabling the checkbox Ignore PDF Rendering Intents prevents the rendering intent of the PDF file from being used, giving the priority to the rendering intents which have been preset in ZePrA under Images/Vectors. Note that in this situation, the rendering settings are 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.
Photoshop PSD and TIFF Conversion
ZePrA 7 and higher allows to convert Photoshop PSD and TIFF files with layers. Layers can be deleted or retained depending on the requirements for further processing of the image files.
- Remove – keep Transparency
Considers only visible layers for conversion. All image elements and text are color converted. Removes layers but transparent areas can still be used and seen. With regard of layers the resulting image will be similar to Photoshop’s Merge visible option.
Note: Make sure to enable only those layers of the PSD file that are supposed to be visible in the converted file before converting with ZePrA.
- Remove – no Transparency
Results in a converted PSD file without any layers and without transparency. With regard of layers the resulting image is similar to Photoshop’s Flatten option.
- Remove – add Transparency Channel
Generates a converted file that has no visible transparency (the areas with checkerboard are gone). Visibly the file looks the same as converted with Remove – no Transparency. In contrast to this option all areas that had transparency in the original file are retained and added in an alpha channel called Transparency. This allows for further editing of the alpha channel mask in Photoshop. The mask can as well be used for reintroducing the transparency into the file, if required.
- Retain Layers, if possible
Retains all layers and their visibility status, if this is possible. All layers will be converted including those that are disabled.
Notes: ZePrA allows conversion to a Multicolor profile but in this case layers can not be retained. The reason is a limitation of Photoshop which does not support spot colors in a layer – please read the General Considerations below. If ZePrA recognizes a Multicolor target profile layers will be removed and a job warning is displayed.
If ZePrA can’t convert a text layer, the following job warning is displayed: A text layer has possibly not been color converted.
- Layers and transparency are special Photoshop functionalities which may not be used by other applications.
- Especially for TIFF files layers and transparency will mainly work in Adobe Photoshop and partly in other Adobe applications but might not work in other apps. In order to retain transparency in TIFF files, for example to place the file in Adobe InDesign, you should check the Save Transparency checkbox in Photoshop’s TIFF Options dialog. If this option is enabled placing works also with the converted TIFF file, with the exception that the preview in InDesign’s placement options dialog is opaque.
Note: TIFF is supported by ZePrA if the Pixel Order is set to Interleave. The alternative pixel order Per Channel is not supported.
- Color conversion images with retaining layers may yield different visual results compared to the flattened images. This depends on several aspects which can all have a big impact on the color view of converted images with layers in Photoshop:
a) Photoshop always calculates the preview of an image with the layers in its stacking order and visibility. This is true except for spot colors which are overprinted on top of the fully composited image.
b) Spot colors can not be in a layer. Read more about the limitations of spot colors in Adobe Photoshop’s online help.
c) The layer effects used: Adjustment layers are not converted when converting with retaining layers in ZePrA which can have a different effect on the converted file than the adjustment layer had on the original file. In some cases adjustment layers can’t work properly in Photoshop if the color space has changed after conversion. A job warning message will be displayed if a color space change (called mode change in Photoshop) has been done with files with adjustment layers.
d) Photoshop layers with smart objects will not be converted when converting images with layers and layers are to be retained. In this case the content of the smart object will not be changed and left the way it is. This can cause some issues, especially if color spaces have been changed (e.g. RGB to CMYK).
e) Transparency effects added to layers might look different after conversion.
Note: If color accuracy is the most important aspect of your PSD and TIFF file conversion, we recommend using one of the layer removing options. If it is more important to edit layers after color conversion rather than color accuracy then use the Retain Layers option.
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 and preserves 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.