Serendipity Blackmagic / Megarip uses an ICC-based colour management system. When created, output ICC profiles use combinations of all available printer ink channels to define colours within the printer’s gamut. All colours output, including solid process colours – cyan, magenta, yellow and black – are made up of a mix of several printer inks.
In certain circumstances, such as in jobs that include fine black lines or text, using dots from multiple ink channels to produce black can cause these elements to lack clarity or sharpness when printed.
When enabled, the Retain Pure Black feature overrides ICC-defined CMYK blacks, replacing them with black printer inks only for job areas defined as black (K).
Retain Pure Black is enabled via a checkbox in the Jobticket > Colour Management tab. It can be enabled in two modes:
- All – Black ink only is used for all black (K) areas of the job, defined as
- C/M/Y = 0%, K ≥ 10%
- Text Only – Black ink only is used for all solid black (K) areas and text elements of the job, defined as
- C/M/Y = 0%, K ≥ 99%
Note – While using Retain Pure Black, can improve the clarity and sharpness of text and fine lines it can also cause a colour shift in the black areas of jobs output by printer models with light black inks that have a non-neutral hue.
Retain Pure Black for CMYK output
The examples below are captured from Softproof Colourspace Dump image sections of the QuickCal test print. (see Serendipity Client > Server menu > Server Settings > Debug tab).
The images show the ink channel values sent to the printer for 100% and 50% Black patches with Retain Pure Black disabled, enabled set to All, and set to Text Only.
100% patch
100% Black patch. CMYK output. Retain Pure Black disabled.
100% Black patch. CMYK output. Retain Pure Black – All.
100% Black patch. CMYK output. Retain Pure Black – Text Only.
50% patch
50% Black patch. CMYK output. Retain Pure Black disabled.
50% Black patch. CMYK output. Retain Pure Black – All.
50% Black patch. CMYK output. Retain Pure Black – Text Only.
Retain Pure Black for RGB output
Serendipity Blackmagic / Megarip 7.1.01+ added to ability to use Retain Pure Black for RGB output sent to Printer’s Screening/HTM printer drivers in RGB mode.
In RGB mode, Blackmagic / Megarip has no direct control over the printer inks used to reproduce RGB defined colour values.
In this case, Retain Pure Black seeks to equalise the RGB values for black areas, in effect placing them on the RGB black/grey axis.
The RGB values are subject to the linearisation (gradation) curve assigned to the Media and as such will be very close, but not quite equal in value.
Note – for an RGB Media with no linearisation curve attached, Retain Pure Black will send equal RGB values to the printer. e.g. 100% K will be sent as RGB 0/0/0.
The examples below are captured from Softproof Colourspace Dump image sections of the QuickCal test print sent to an RGB output.
The images show the RGB channel values sent to the printer for 100% and 50% Black patches with Retain Pure Black disabled, enabled set to All, and set to Text Only.
100% patch
100% Black patch. RGB output. Retain Pure Black disabled.
100% Black patch. RGB output. Retain Pure Black – All.
100% Black patch. RGB output. Retain Pure Black – Text Only.
50% patch
50% Black patch. RGB output. Retain Pure Black disabled.
50% Black patch. RGB output. Retain Pure Black – All.
50% Black patch. RGB output. Retain Pure Black – Text Only.
Retain Pure Black for RGB output with no linearisation curve
The examples below are captured from Softproof Colourspace Dump image sections of the QuickCal test print sent to a HP Pagewide XL printer via a Media with no linearisation curve attached.
100% patch
100% Black patch. RGB output. Retain Pure Black – All. No linearisation applied.
50% patch
50% Black patch. RGB output. Retain Pure Black – All. No linearisation applied.