Images and Vectors
The processing of CMYK, RGB, Gray, and Lab objects (images and vectors) can be individually defined and precisely controlled. For the conversion, both images and vectors can be an assigned device or DeviceLink profiles, or embedded profiles can be used. Alternatively, the SmartLink function can be used to create high-quality DeviceLink profiles “on-the-fly” for the conversion of any object.
By default, the same settings are used to convert images and vectors, but they can also be processed independently using custom settings.
The rendering intents selected under Images/Vectors are only used for the conversion of PDF files under certain conditions – see below. For image data such as TIFF, JPEG, PSD, and PSB, the rendering intents selected under Images are automatically used.
Image Color Conversion
The panel Image Color Conversion provides settings to convert individual images such as TIFF, JPEG, PSD and PSB files or images within a PDF file. There are three conversion settings for CMYK, RGB, Gray and Lab:
- No Conversion: Images are not converted
- Convert to Document Color Space: First converts the image data to the ICC device profile selected as the Document Color Space in the Document/Target tab. In the second step, the conversion settings made in the Document/Target tab are applied to the image data. This often leads to a second conversion of the image data – according to the settings – into the target profile set under Target Color Space.
Notes: In the PDF context, conversion to the Document Color Space is also referred to as normalizing and is common practice. For the conversion of pure pixel data (PSD, TIFF, JPEG) the two-step conversion using Convert to Document Color Space is usually not recommended.
- To Target Color Space: Converts the image data from the source color space to the profile selected under Target Color Space without first converting it to the Document Color Space.
Use CMYK Conversion: Files composed of grayscale images can also be converted using the setting Use CMYK Conversion. The gray components are converted with the same settings used for CMYK. If a DeviceLink conversion by SmartLink is selected under CMYK, the gray images remain gray even after the conversion and are not built up in four colors.
The SmartLink function uses the source profiles embedded in an image’s data and automatically. ZePrA then calculates the DeviceLink profile required for conversion between source and target profiles for each object and applies the profile at object level.
If there are no embedded profiles (or if they are to be ignored) and Same as Document Color Space is set, SmartLink creates a DeviceLink using the Document Color Space and Target Color Space. The document color space is the profile selected as the Document Color Space under Document/Target, or the output intent of the PDF file if Prefer Output Intent is selected.
If you want to use the rendering intent set under Configurations > Images/Vectors for the conversion instead of the embedded rendering intents, activate the Ignore PDF Rendering Intents checkbox in the Options tab.
Apply Embedded Profiles/Intents: Uses embedded ICC device profiles and embedded rendering intents of the PDF file for CMYK, RGB, Gray images, or vector data.
The embedded rendering intent is used together with the embedded profiles, and the manually set rendering intent is ignored.
To ensure high-quality color conversions without loss of accuracy when using embedded rendering intents, the Black Point Compensation checkbox should be activated in the Options tab.
Vector Color Conversion
Vector Color Conversion defines how individual vector objects of a PDF file are processed. By default, vectors and images are converted with identical settings, but they can also be processed independently with custom settings:
Convert like Images: The default setting. Vector objects are converted with the same settings as images.
Note: For PDF files with flattened transparencies, it is likely that pixel and vector data of the same color are directly adjacent. If images and vectors are converted with different settings, color differences may occur between adjacent pixel and vector objects of the same color. Images and vectors are therefore converted with identical settings by default. This avoids color differences.
Don’t convert: Vector data is not converted, whereas image data is converted.
Apply the following Settings: Allows to define individual conversion settings for CMYK, RGB, Gray, and Lab.
The following three conversion settings are available:
- No Conversion: Vectors are not converted.
- Convert to Document Color Space: First converts the vector data to the ICC device profile selected as the Document Color Space in the Document/Target tab. In the second step, the conversion settings made in the Document/Target tab are applied to the vector data. This often leads to a second conversion of the vector data – according to the settings – into the target profile set under Target Color Space.
Notes: In the PDF context, conversion to the Document Color Space is also referred to as normalizing and is common practice.
- To Target Color Space: Converts the vector data from the source color space to the profile selected under Target Color Space without first converting it to the Document Color Space.
Use CMYK Conversion: Files composed of grayscale vectors can also be converted using the setting Use CMYK Conversion. The gray components are converted with the same settings used for CMYK. If a DeviceLink conversion by SmartLink is selected under CMYK, the gray vectors remain gray even after the conversion and are not built up in four colors.
To ensure high-quality color conversions, DeviceLink profiles should be used with or without SmartLink.
Generally, the rendering intents are defined for each object in the PDF and are used by ZePrA when the Apply Embedded Profiles/Intents checkboxes in the Images/Vectors tab are checked. To use other rendering intents, for example, the high-quality rendering intents of ColorLogic, the checkbox Ignore PDF Rendering Intents must be checked in the Options tab.
The selection of a suitable rendering intent is crucial for the optimal conversion of PDF objects. Therefore, separate rendering intents can be used for the conversion of CMYK, RGB, Gray, and Lab objects.
To ensure precise color conversions, ZePrA completely recalculates the conversion of source and target profiles on-the-fly. The same algorithms are used as in ColorLogic’s CoPrA profiling software.
In addition to the standard rendering intents, ZePrA contains five more rendering intents that are only available with the SmartLink option activated.
Additional SmartLink Rendering Intents
The SmartLink module provides seven additional rendering intents to avoid inharmonic color conversions, which can result from differently calculated tables for source and target profiles.
To ensure precise color conversions, ZePrA completely recalculates the conversion of source and target profiles on-the-fly. The algorithms are the same as ColorLogic’s CoPrA profiling software.
Note: These additional rendering intents are only available with SmartLink enabled. If the checkbox Use SmartLink is not activated or SmartLink has not been licensed, only the four standard rendering intents are available.
Standard Compression: For conversions involving different gamut sizes. Calculates a perceptual conversion for input and target profiles that is suitable for all types of gamuts. The appearance of the gray axis always depends on the paper white of the target profile. With CMYK data on a very yellowish paper, the gray axis of the converted file also looks yellowish. The same gray axis will look bluish on bluish paper. The Standard Compression considers different gamut sizes. For very small color gamuts (newspaper printing), the dark tones are slightly raised to achieve more definition in these areas.
Black Point Compensation: Use Black Point Compensation to achieve the same results with a perceptual conversion as with “Relative Colorimetric with Black Point Compensation”. When converting from a large to a small color space, the image definition is preserved in the highlights and shadows, unlike with a pure Relative Colorimetric conversion. Neutral tones are converted using the colorimetric intend. Out-of-gamut colors are cut off.
Absolute Compression: For conversions where the color gamuts are similar but the paper tones are clearly different. In contrast to the Standard Compression and Black Point Compensation, the gray balance compensates for the paper color. This ensures that the color impression of the original file is preserved in the best possible way on a target medium with a different paper color. This method also raises shadow (darker) areas when using small color gamuts.
The gray axis of a source color space will look similar to the original after conversion (for example, on a yellowish or bluish paper).
Dynamic Compression: Compares the source color space with the target color space and generates a compression that minimizes out-of-gamut areas. This setting preserves the brightness of the original color space while reducing the saturation, and therefore preserves the image definition. As for the Standard Compression, the gray axis of the conversion is built relative to the paper white of the target profile.
Minimum Compression (Paper Absolute): This method is largely similar to the absolute colorimetric intent and only compensates close to the black and the white point. Maximum shadow contrast will be achieved and image definition will be preserved while the paper white will not be simulated. Use this rendering intent if you would like to achieve a very close reproduction, for example when using print standards like ISO Coated V2 or GRACoL2006 Coated1v2 on a digital printer.
Note: As for the absolute colorimetric rendering intent, ensure that the target color space is larger or has at least a similar size to avoid any loss of image definition. For color conversions from larger to smaller color spaces use Absolute Compression to maintain the gray balance of the source color space.
Minimum Compression (Paper Relative): This method is largely similar to the relative colorimetric intent and only compensates close to the black and the white point. It is similar to Minimal Compression (Paper Absolute) but uses relative colorimetric instead.
Minimum White Compression: This method is similar to Minimum Compression (Paper Absolute). Both rendering intents compress the white point without paper simulation, however, there is an important difference: The Minimum Compression is a rather perceptual rendering that additionally compresses the black point so the maximum dynamic range is utilized without loss of detail in the shadows. In contrast, the Minimum White Compression compresses the white point but not the black point, so a close absolute colorimetric match between source and target color spaces can be achieved. This can be useful for the color representation across various media, color matching or printing on slightly differing media. It can be regarded as close to absolute colorimetric rendering without paper tint simulation.
Important: To ensure that an on-the-fly DeviceLink profile created with SmartLink uses the rendering intent set under Configurations > Images/Vectors, activate the checkbox Ignore PDF Rendering Intents in the Options tab.