The full formula is:
Highlight minimum dot size = lowest_printing_tint *
(device_resolution / screen_frequency^2
You can do a similar calculation for the other end of the tone scale, in
the shadows. For example, if you can print as much as 85% at 150 lpi
before totally plugging, then:
(100% - 85%) * 256 = 38 device pixels
So the formula is:
Shadow minimum dot size = (100% - highest printing tint) *
(device_resolution / screen_frequency^2
The reason why the control specifies the minimum dot size in device
pixels rather than a tint value is because, for a given printing process,
the number of device pixels that can be reliably printed is usually
constant, while the same number of device pixels corresponds to
different actual tint values as you change the screen frequency. So, the
idea is that you set the minimum/maximum dot value once for your
press/plate combination, and leave this setting alone, even if you
change to some other screen frequency.
Screen types
Maxtone
Maxtone uses AM screening to create tonal values above the minimum
dot size. Once the minimum dot size is reached, Maxtone uses an FM-
like technique to progressively remove minimum-sized dots from the
AM grid. This technology allows flexo printing to achieve increased
highlight values, using the minimum printable dot size.
Maxtone CX
Maxtone CX hybrid AM screening feature enables printers to configure
the size of highlight and shadow dots to suit the resolution-rendering
capabilities of their output device, plate, and pressroom.
The dots in Maxtone CX are arranged on the same screen-ruling grid
as Maxtone screens, and tonality in the midtones is controlled by
adjusting the size of the dots. However, for Maxtone CX, tonality in the
highlights and shadows is controlled by fixing the dot width and
varying the number or frequency of dots placed on the grid.
Maxtone CX is particularly useful in resolution-limited applications in
which Maxtone highlight or shadow dots are not rendered reliably or
consistently. For example, Maxtone CX is useful in flexo packaging,
where highlight scum dots do not print reliably, in heatset web
applications, and where highlight dots do not have the same run-length
durability as the midtones.
Screen types
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