When creating an ICC characterization profile, it is defined how the color values of the source color space are separated into the channels of the printing system. Black Start is one of the key parameters of black generation. It defines the tone value at which the Black Channel is first introduced into the separation. Below the defined Black Start, neutral tone values are built exclusively from the chromatic colors Cyan, Magenta, and Yellow. Only from the defined tone value onward is Black added to the separation, progressively replacing the neutral components of the chromatic colors.

Black Start therefore determines the threshold at which the Black Channel is introduced, while its subsequent progression is defined by the other black-generation parameters, in particular Gray Component Replacement (GCR). In conventional CMYK separations, Black Start affects only the use of the Black Channel. Additional Process Colors in an extended color configuration, such as Orange, Green, or Violet, are controlled by separate separation strategies.

Figure 1: Black Start principle along the gray axis (schematic)

Black Start is specified as a percentage value between 0% and 100% and defines the tone value at which the Black Channel is first introduced into the separation:

• Black Start 0% – the Black Channel is introduced even in the lightest tone values. The black curve starts directly at the zero point, meaning that small amounts of Black may already be present in the highlights.
• Black Start 30% – tone values up to 30% are built exclusively from Cyan, Magenta, and Yellow. From a tone value of 30% onward, the Black Channel is added to the separation and increases continuously toward the shadows according to the defined black curve.
• Black Start 100% – the Black Channel is effectively not used. The tonal range is built almost entirely from Cyan, Magenta, and Yellow.

Figure 2: Black curves at different Black Start values (schematic)

You can find the Black Start parameter [1] in a Profiling Project under the Separation Parameter tab in the Create Characterization Profile step.

Figure 4: Options in the Separation Parameter tab of the Create Characterization Profile step

The parameter defines the tone value at which the Black Channel is introduced into the separation. Values can range from 0% to 100%. A higher value means that highlights and light midtones are built exclusively from Cyan, Magenta, and Yellow over a wider tonal range. The Black Channel is therefore introduced into the separation only at darker tone values.

Shifting the introduction threshold controls the tone value from which black halftone dots appear in the print result. At the same time, Black Start affects the tonal range in which Gray Component Replacement (GCR) can take effect, because Black is only available to replace the neutral components of the chromatic colors from the defined introduction point onward.

The following recommendations apply when using the parameter:

• Black Start 30% (default value) – a Black Start of 30% provides a balanced compromise between image quality in the highlights, process stability, and ink consumption. The highlights are built exclusively from Cyan, Magenta, and Yellow, resulting in a smooth and homogeneous appearance. Black is introduced into the separation from the midtone range onward. This reduces the dependence of the gray balance on fluctuations in the chromatic colors and allows Gray Component Replacement (GCR) to take effect.
• Black Start 0% (early black introduction) – at a value of 0%, Black is introduced even in the lightest tone values. This can reduce the consumption of chromatic colors because their neutral components are replaced by Black at an early stage. This approach is often used in ink-saving profiling strategies. Please note that black halftone dots have a high contrast against the substrate in light image areas. Depending on the screening technology and print resolution, this can make highlights appear grainier.

• Black Start 60% or higher – with a high Black Start, highlights and light midtones are built exclusively from Cyan, Magenta, and Yellow over a wider tonal range. The finer halftone dots of the chromatic colors can produce a particularly smooth and homogeneous image appearance, for example in light gradients, skin tones, or large neutral areas. However, the consumption of chromatic colors increases because Black is not available to replace neutral components in these areas. Please note that the gray balance in the highlights and midtones is therefore generated exclusively through the chromatic colors and is more sensitive to fluctuations in the printing process. In addition, the tonal range in which Gray Component Replacement (GCR) can take effect is reduced.

Please note that Black Start can also be configured in other areas of the Create Characterization Profile step.

• The Use Black Start even for Pure Black option in the Gamut Adjustment tab additionally applies the Black Start threshold to the generation of pure Black.
• The Black Start parameter in the Spot Colors tab defines the threshold at which the Black Channel is introduced when separating Spot Colors. However, the calculation follows a different logic: the average of all CMY percentage values is used to determine the Black Start.