ZePrA | Apply Photoshop color corrections to PDF files

Apply Photoshop color corrections to PDF files

In some applications it is not possible to use measurement based DeviceLink profiles. This is true, for example, if a customer brings print data and a print that should be as accurate as possible in the production run without a correct proof. If you view the print data on a monitor with a soft proof of the print standard for the production run, clear deviations from the print that you have brought with you can become visible.

In this case you could either print outside the standard and try to recreate the default – either by making gradation corrections in ZePrA or by using the capabilities of the printing press – or print inside the standard by applying Photoshop corrections to the PDF file. The latter has the advantage that you can proof the color-corrected data according to the standard and have it approved by the customer. This procedure requires an experienced Photoshop user and CoPrA’s Editing tool.

For a test with production data the demo version of the programs can also be used. To do this, meaningful objects must be combined from the existing PDF data into one file in Photoshop and combined with CoPrA’s test chart (EditTarget). This test file is then corrected under softproof conditions on the monitor. The edited image is imported into CoPrA and the corrections are taken into account in the created DeviceLink profile.

Then the DeviceLink profile can be used in ZePrA to correct the color of the original PDF data. If necessary, the corrections can be approved by the customer on a proof before printing. The printer can work as usual according to standard and reach the proof reliably.

The individual steps are described in detail in the chapter How to create DeviceLink profiles with edited charts in the CoPrA Help.

ColorLogic’s Printer Profile PSOcoatedv3_GCR_ColorLogic.ICC explained

PSOcoatedv3_GCR_ColorLogic.ICC profile

ColorLogic’s Printer Profile ‘PSOcoatedv3_GCR_ColorLogic.ICC’ explained

PSOcoated_v3_GCR_ColorLogic vs. PSOcoated_v3

Tutorial: ColorLogic’s Printer Profile ‘PSOcoatedv3_GCR_ColorLogic.ICC’ explained


Optimized Printability for neutral Image Areas

This profile is an alternative to the ICC profile ‘PSOcoated_v3‘ from the ECI. It is based on FOGRA51 characterization data and offers optimized printability for neutral image areas.

Details on PSOcoatedv3_GCR_ColorLogic.ICC

Good printability in offset printing requires optimized GCR settings (Gray Component Replacement) and a fine-tuned balance of K and CMY in separated images. When RGB images are converted to CMYK using ICC profiles the GCR settings are fixed in the CMYK printer profile and specified during ICC profile generation.

The example below shows a comparison between the GCR settings of the ECI profile ‘PSOcoated_v3.ICC’ and ColorLogic’s alternative profile:

The two main differences in regard of GCR settings of our ICC profile ‘PSOcoated_v3_GCR_ColorLogic‘ and the ‘PSOcoated_v3‘ profile from the ECI are:

1) Neutral images are printed more stable: Maximum GCR in neutrals

The original ECI profile features a medium GCR which is similar in both neutrals and skin tones. In contrast, ColorLogic’s profile has a maximum GCR in neutrals but is reduced in tertiary colors like skin tones. This GCR strategy combines the best of both worlds: A maximum GCR for neutral colors to prevent color casts as far as possible or unstable gray balances during printing. A medium GCR for skin tones to prevent grayish skin tones in case black is printed too strong.

2) More stable printability for light image areas: Black starts at zero

When using ColorLogic’s profile, black starts at zero and replaces similar CMY values. This stabilizes areas of light neutral colors. RGB images which contain neutral vignettes or drop shadows from gray to white will be printed more stable.

Links and Downloads

 

ZePrA | Spot color processing

Spot Color Processing

The spot color module of ZePrA allows spot colors of PDF files to be converted accurately into CMYK, RGB or Multicolor color spaces. It requires a spot color license, which is included in ZePrA XXL, but can also be purchased as an Add-on module.

The spot color module

  • is part of ZePrA XXL, including a Multicolor license.
  • is available as an Add-on for ZePrA (requires a spot color license).
  • is part of the Multicolor Add-on (requires a Multicolor license).

Spot Color Libraries

Spot Color Libraries and spot colors can be clearly managed in ZePrA’s spot color module. It can be opened with a click on Spot Color Libraries in the sidebar.

Here libraries can be created, added, viewed and customized. Individual spot colors can be edited, imported or measured. For example, spot colors from color fans can be measured with a spectrophotometer or Lab values can be entered manually. Color tables with spot colors can also be imported. Supported formats are Named Color ICC profiles, Photoshop ACO color tables, Adobe ASE color tables (from InDesign or Illustrator), text files in CGATS format or CxF files, such as CxF/X-4. You can import your PantoneLIVE color fans stored in the cloud using the PantoneLIVE button.

Note: PantoneLIVE® from X-Rite is a cloud solution for digital storage of spectral spot colors. For using PantoneLIVE, licenses for the spot color module of ZePrA and for PantoneLIVE from X-Rite are required. Under My X-Rite you must unlock your licenses for use in ZePrA. For information on how to do this, see PantoneLIVE.

Both Lab and spectral color values are supported. Spectral measurement data are to be preferred, as they give the best results internally.

For more information about spot colors and spot color libraries, see:

Spot Colors

Edit Spot Color

PantoneLIVE

Converting spot colors to pixel-based formats: Spot colors from image files (ZePrA supports the pixel formats TIFF, PSD and PSB) can be converted by generating the spot colors as alpha channels with spot color attribute.

Without spot color module: The alternative replacement colors specified in the PDF file are used to convert spot colors to the target color space, resulting in reduced quality. For more information, see Working without the Spot Color Module.
Note: In many cases, standard conversion without the use of a custom spot color library will not result in a sufficiently good spot color reproduction or a good printing replacement process color.

Retain user-defined spot colors: Maintaining custom spot colors is critical to print production. For example, in packaging printing, this is necessary to preserve areas for die cut, braille, varnish, fold and crop marks.

Spot Color Processing – The Classic Method

Normally, spot colors (DeviceN colors without CMYK components) are resolved and converted into the target profile. The replacement color (Alternate Color Space or replacement color in the PDF) that is assigned to each spot color in the PDF is used. The PDF alternate color space for a spot color is usually specified in CMYK or Lab and is specified in the PDF-creating graphics or layout application (for example Adobe Illustrator, InDesign or QuarkXPress).

By using the appropriate settings, ZePrA performs a DeviceLink conversion from the replacement color to the target color space. Nevertheless, conversion with the replacement color value is a rather inaccurate solution, especially if the replacement color for the spot color is specified with device-dependent CMYK values. But even if the replacement color is defined by a measured Lab value, the ICC color conversion results in a color conversion that is mostly not sufficiently accurate and above all not well printable.

Example: The spot color PANTONE 266 C of a PDF document has an alternate color value of CMYK = 70/81/0/0. Printed in high-quality offset printing on coated paper according to ISO Coated V2, these CMYK process color values would produce a dark violet color that is 32.7 DeltaE-76 or 9.8 DeltaE-2000 away from the actual spot color (see screenshot). The color lies outside the printable color gamut and is therefore not printable in four-color offset printing.

The same spot color with the same PDF replacement color value would also only be reproduced with a large color error of approx. 9 DeltaE-2000 in a Multicolor printing system with 7 colors, which could simulate the spot color very well. In our example, a conversion via a stored CMYK replacement color value will therefore lead to an extremely unsatisfactory color reproduction in both printing processes.

Working with spot colors

An exact conversion of spot colors requires color libraries with correctly measured spectral color values on the one hand, and additional DeltaE minimization on the other. With a DeltaE minimization, our example colour PANTONE 266 C in the Multicolor 7C printing process could even be reproduced exactly without color errors (see screenshot).

Often several Spot Color Libraries are created for identical spot colors because it is necessary to use separate and optimized color values for different substrates or printing processes.

Spot Color Libraries can use measured gradations of spot colors, so that gradations of the spot color can be reproduced optimally (for example, the 50% value of a spot color).

In order to better calculate overprint simulations, the measured values can be stored spectrally (also spectrally on black color). Then the calculation is done with an intelligent spectral color mixing model.

ZePrA is able to maintain overprinting properties if this is possible.

For elements consisting of a mixture of spot colors and other process colors, the color appearance is simulated in the best possible way after the spot color has been resolved.

When converting to the target color space, as few process colors as possible can be used while still maintaining the smallest possible visual color difference. In our example, the optimal solution is to use only the violet process color (see screenshot) and still achieve a color error of only 1.0 DeltaE-2000.

Spot colors can be converted to a desired target value (for example, a process color) regardless of the smallest possible DeltaE. This is necessary for texts or barcodes, among other things.

Spot colors can be excluded from a conversion, for example when spot colors are used as crop marks, gloss varnishes or braille characters.

ZePrA | Working with Transparencies

Working with Transparencies

Working with Transparencies

Transparency Flattening and Sharpening

Many users often think of only photographic images when sharpening PDF data.  However, when flattening transparencies, vectors and texts can also be converted into pixel-based images. These pixel-based images are treated like photos when the Sharpening option is activated This can lead to adverse results. A difference in sharpness between adjacent objects in the form of a vector or text can cause visual issues and inconsistencies. For production, sharpening effects should always be tested in advance.

Use caution when flattening transparencies with ZePrA. Sharpening takes place before conversion and flattening. In contrast, sharpening without transparency reduction in ZePrA takes place after conversion.

Depending on the composition of the elements in the layout software on the one hand, and the parameters for flattening the transparencies and sharpening in ZePrA on the other, extreme sharpening can produce visually undesirable effects.

The negative effects only become apparent at the most extreme sharpening Amount with a Threshold of 0. Since JPEG artifacts usually show minimal color differences, a high Threshold is the most important factor to avoid unwanted effects.

The following example shows the effects of different sharpening levels. In this case, the graphic designer has placed an object with drop shadow over a gradient.

When flattening the transparencies, the flattened elements were compressed using the JPEG format. With an extreme sharpening setting, the artifacts part of the gradient underneath the drop shadow, which is usually invisible, become intensified when converted into a JPEG image. The following sharpness settings were used from top to bottom:

  • No Sharpening
  • Radius 0.35 points, Amount 80, Threshold 8
  • Radius 0.35 points, Amount 300, Threshold 4
  • Radius 0.35 points, Amount 500, Threshold 0

 

Converting PDF files containing transparencies

When converting PDF files with transparencies, the transparencies can either be preserved or flattened using Transparency Flattening.

During conversion, each object – with or without transparency – is converted separately, preserving the structure of the PDF document.

Unfortunately, there are so many variations in the blending of transparencies and the stacking order of semi transparent objects that there is no simple rule as to when transparencies ought to be flattened or not.

Flattening requires the resolution of the platesetter to be specified; therefore, it is best to perform transparency reduction as late as possible in the workflow.

ColorLogic recommends performing the conversion in ZePrA first without transparency flattening and then to check the converted file with a transparency-compatible PDF viewer (e.g. Adobe Acrobat Pro or Callas PDF Toolbox). If the converted file is visually correct and the desired total amount of coverage is maintained, continue working with the file.

If the file contains artifacts after conversion, uncheck the Convert all transparent Elements in PDF Files checkbox under Configurations/PDF and convert the file again.

This changing this setting often helps to preserve the impression of the original file (see figure below), since ZePrA excludes certain transparency modes from the conversion.

The checkbox Convert all transparent Elements in PDF Files is active by default.

However, if there are still artifacts after deactivating this function, use Transparency Flattening.

Note: Transparency Flattening is based on the Callas SDK, which in turn uses Adobe’s PDF engine for transparency flattening. Therefore, the results achieved with ZePrA’s Transparency Flattening are identical to those achieved with the current versions of Callas pdfToolbox.

Converting Spot Colors containing Transparencies

For transparency flattening of PDF files containing transparent objects composed of process and spot colors, Adobe’s transparency flattening preserves spot colors to preserve the impression of the original but sets them to “Overprint”. Transparency-reduced PDF files should therefore always be viewed with “Overprint preview” enabled in the PDF viewer (e.g. Adobe Acrobat Pro). Simple PDF viewers, such as the Preview in macOS, or many apps on tablets, display such files incorrectly due to the missing overprint feature.

If ZePrA is to be used for high-quality spot color conversions instead of the PDF preflight program or the RIP, activate the checkbox Convert Spot Colors under Configurations/Spot Colors and spot colors are converted to process colors in the best possible way.

Note: Spot colors that are converted will be set to “Overprint” due to the transparency reduction and can mix with process colors. This can lead to unwanted results and the disappearance of converted spot color objects. If this happens, select Transparency Flattening and either Dissolve Overprinting or use the extreme method Rasterize Document.

Transparency Flattening, Image Quality, and File Size

When reducing transparencies, the resulting rasterized objects are created with lossless ZIP compression. This guarantees the best quality but also results in larger files compared to JPEG compression. Even PDF files with JPEG-compressed images will have ZIP-compressed images due to transparency flattening. If the file size is to be reduced, and a reduced quality is acceptable, change the Compression Method to JPEG (in the Image Quality panel under Configurations/Options).

Note: The Compression Method is only considered by ZePrA when performing a conversion. When performing a Transparency Flattening without conversion, no compression change is made, and rasterized objects are ZIP-compressed.

ZePrA | Sharpening

Sharpening

(For example, in-house RGB workflows)

Sharpening Images

Optimal sharpening refers to the scaled final format of an image in the print data. The following section assumes that editing high-resolution RGB images, placing these images in the layout program, creating the PDF data, and processing the data with ZePrA are connected workflows within an application suite. The summary of these steps is referred to here as an in-house RGB workflow.

With in-house RGB workflows it is possible to work with high-resolution originals of the RGB images in the layout program and then generate a PDF/X-3 or PDF/X-4 file that also contains high-resolution RGB images. Finally, ZePrA handles the color management, the downsampling to the final resolution, and the sharpening. 

After the RGB images have been reduced to the final resolution and color converted to CMYK, a stronger sharpening than is usual for pre-sharpened CMYK images should be applied in ZePrA. To do so, select Strong Sharpening of RGB and Gray Images in ZePrA under Configurations/Options/Sharpening/Preset.

For documents that contain RGB images and already sharpened CMYK images it is recommended to limit sharpening in ZePrA to RGB images.

Note: If transparencies are used in the layout program, it is essential to ensure that there is no  transparency reduction, as RGB data is inevitably converted to CMYK if the RGB image is affected by transparent objects. Transparency reduction is mandatory when creating PDF/X-3 files, whereas transparency is explicitly allowed in PDF/X-4 files. If all RGB images are sharpened in ZePrA, the transparency reduction, should also take place in ZePrA.

ZePrA | Screen Preview

Screen Preview

Previewing PDF and image files

Previewing PDF and image files

ZePrA’s Screen Preview displays a true color representation of files processed via queues on the monitor, with overprinting elements and transparency effects displayed correctly.

How to display a Screen Preview

  1. Open the Overview from the sidebar.
  2. Right-click a job in Pending Jobs or Processed Jobs to open the context menu.
  3. Choose Screen Preview.

  4. Your file will open in a new window.

  5. The colored symbol in the title bar can be used to access and adjust the color management settings for the screen preview. The preview is displayed according to these settings.

Simulation Profile: The colors are rendered to the monitor profile using the selected simulation profile. By default, the output intent that was embedded into the processed file by ZePrA is used. It is displayed in brackets. This setting is similar to the output preview of Adobe Acrobat.

Note: The Default Profiles and the checkbox Prefer embedded Profiles are only relevant if the Simulation Profile differs from the color space of the file.

Rendering Intent: A color conversion method (rendering intent) must be selected for the calculation. In addition to the standard ICC-Intents, there are four extra ColorLogic intents:

  • Black Compensation
  • Relative+ and Absolute+: Only have an effect if the black point in a matrix monitor profile is lighter than L* = 0, which makes the Screen Preview slightly darker, especially in the shadows, which usually results in a visually better match with a reference proof.
  • Relative Lightness: Is based on the Absolute Colorimetric intent with paper tone simulation. The brightness of the paper tone simulation is scaled to the maximum displayable brightness of the monitor, whereby the colorfulness of the paper tone simulation and the gray balance of the preview as a whole are preserved. This setting is useful if the absolute colorimetric preview provides a visually too dark display, as is often the case in newspaper printing.

If no simulation profile is available in the file (no profile is shown in brackets), select the appropriate profile from the drop-down list. Suitable rendering intents here are the colorimetrically based and the special ColorLogic intents.

The monitor profile stored in your system is automatically selected to display the screen preview on your monitor.

Click Apply to view the selected file with these settings and Save to save and close the window with these settings. The next time you open the window, these settings will be used again.

Note: In general, it is recommended to use a dimmable standard light box with a reference proof next to the monitor for visual comparison when selecting the correct screen preview intent.