General information on the design of ICC device profiles
Rendering intents, such as Perceptual or Relative Colorimetric, contain large tables which, for example for CMYK profiles, convert either CMYK color values to Lab or Lab color values to CMYK.
Due to these two color conversion directions, there are two tables for each rendering intent. The tables are calculated from the measurement data when a color profile is generated.
If ICC device profiles are calculated from the same measurement data, but with different profiling programs, then the tables generated can differ considerably in some color ranges.
This is especially true for the two tables of the Perceptual intent, for the gray balance and also for the areas with very high color saturation in the two tables of the Relative Colorimetric intent (also called "Out of Gamut" colors).
For optimal and harmonious color conversion, it is recommended, especially with CMYK-to-CMYK color conversions, to ensure that the source and target profiles were calculated with the same profiling software.
However, profiles from different providers (such as Adobe, ECI or ColorLogic) are often used in practice, which can lead to problems in color conversions if the perceptual rendering intent is used.
These problems can be avoided by using SmartLink.
The SmartLink module uses the source profiles embedded in PDF or image data and automatically calculates the DeviceLink profile required for conversion between source and target for each object and applies it at object level. The main conversion from the document color space to the target color space is also carried out via SmartLink. SmartLink is ideal for processing external data from a wide variety of sources to ensure optimum color accuracy (via DeviceLinks).
Additional SmartLink Rendering Intents
There are several additional Rendering Intents for SmartLinks
The SmartLink module provides several 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.
Automatic from Preset: This option is for Custom SmartLink Methods shared from CoPrA and takes whatever setting has been selected in the shared DeviceLink setting from CoPrA, including the rendering options, like a merge between two rendering options, chroma or saturation boosts, all exceptions and black generation settings.
Note: Automatic from Preset is only available in the drop-down menu when a custom SmartLink Method is selected. So, first select a custom SmartLink Method and the option Automatic from Preset will be on top of the list.
Note: In earlier versions of ZePrA (9 and lower) it is not possible to merge two different rendering options for color conversion, because the rendering settings of a profiling setting shared from CoPrA are always overwritten by the rendering setting selected in ZePrA.
Standard Compression: This is the default method. It uses a perceptual conversion that is well suited for all types of gamuts, i.e., also for conversions between color spaces of different sizes. Neutral tones are converted using a relative colorimetric approach, and the appearance of the gray axis always depends on the paper white of the target profile. Therefore, the gray axis of the transformed file will appear yellowish on a very yellowish paper. The same gray axis will appear bluish on a bluish paper. For very small color gamuts, for example in newspaper printing, the dark tones are raised slightly to achieve more image definition in these areas.
Black Point Compensation: Use Black Point Compensation to achieve the same results with a perceptive conversion as with “Relative Colorimetric with Black Point Compensation”. When converting from large to small color spaces, the image definition is preserved in the highlights and shadows, unlike with a pure Relative Colorimetric conversion. Neutral tones are converted using the Relative Colorimetric intent. Out-of-gamut colors are cut off.
Absolute Compression: This method is based on the absolute colorimetric rendering intent in terms of color reproduction and is recommended when the paper tones differ significantly (the color gamuts can be similar or different). In contrast to the Standard Compression and Black Point Compensation, the paper tint is compensated in the gray balance. The rendering of neutral colors is based on the absolute colorimetric rendering intent, without paper tone simulation in the highlights. If, for example, the paper white is significantly more yellow than in the reference, the gray axis appears neutral despite the yellowish paper tone. This ensures that the color appearance of the original file is preserved as best as possible on a target medium with a different paper tint. The contrast range in the highlights and shadows is adapted to avoid any loss of image definition.
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.
In addition, the white point of the source color space is not simulated, but scaled to the white point of the target color space, thus ensuring a pure paper white.
Use this rendering intent to achieve a close reproduction, for example when using print standards such as 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.
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 also 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. This approach is well suited when the source and target profiles have a very large dynamic range and contrast, for example, in RGB-to-CMYK conversions.
Note: This method is now only available in ZePrA for compatibility reasons, and no longer in CoPrA. We recommend using Automatic Paper Relative 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.
Note: Remember that the target color space should be larger than the simulated color space (or similarly large) to avoid loss of detail and vividness (similar to the absolute colorimetric rendering intent). For conversions from large to small color spaces, instead use our rendering intent Absolute Compression if the gray balance of the source color space is to be preserved.
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.
Automatic Paper Relative: A paper-relative rendering without adjusting the gray balance, which differs between the source and target profiles due to differences in paper tone. A typical use case would be a more colorful rendering of a color space on a different printer where the gray balance does not necessarily need to match. For example, a campaign that has been prepared for ISO coated V2 but is to be printed on a large format inkjet printer. The gray balance is reproduced with the same coloration as the paper color tone of the target profile.
Automatic Paper Absolute: An absolute paper rendering with consideration of the paper color tone. A typical use case would be the same as Automatic Paper Relative, but with the paper color tone of the source profile taken into consideration. This results in a reproduction of the gray balance on the target printer that matches the color tone of the source profile and thus provides the best possible color appearance.
Important: For PDF processing ZePrA typically uses the rendering intent defined in the PDF for each object. When deviating from this rule, ensure that an on-the-fly DeviceLink profile created with SmartLink uses the rendering intent set under Configurations > Images/Vectors, select the checkbox Ignore PDF Rendering Intents in the Options tab.
