Service manual

1.8.6 Digital Halftoning
Generally speaking, 1 bit/pixel and 2 bits/pixel formats cannot express continuous image tones. The
halftoning mode processes the scanned image data so that the data output in these formats simulates
continuous tones when displayed or printed.
The halftoning mode is suitable for use with continuous tone images (such as photographs), and in
conjunction with output devices that cannot handle multi-bus data for each pixel. Halftoning mode is not
suitable for images requiring sharp definitions (line art, characters).
You can select whether or not to use halftoning. When halftoning is disabled, the data format determines
which tones can be reprinted. Halftoning mode is not useful and cannot be selected for data formats of 3 or
more bits per pixel.
If you decide to use halftoning, you may choose one from among three halftoning modes and four resident
dither patterns. When you choose a halftoning mode, the scanner provides a scanned image with continuous
tones, comparing adjustment pixels. When you choose a dither mode, the scanner uses a regular pattern for
the same purpose. Each mode is outlined below.
Halftoning Mode A
This is the standard halftoning procedure. The scanner converts the image into a hard-toned output which
maintains image definition. This mode is suitable for most purposes.
Halftoning Mode B
The scanner converts the image to a soft-toned output. This mode is suited for images in which similar tones
cover fairly large areas.
Halftoning Mode C
Image representation is similar to newspaper image printing (net screening). Tone gradations are represented
by clusters of different numbers of dots.
Dither Mode A
The scanner processes the 1 bit/pixel image by using a 4 × 4 bayer pattern.
Dither Mode B
The scanner processes the 1 bit/pixel image by using 4 × 4 spiral pattern.
Dither Mode C
The scanner processes the 1 bit/pixel image by using 4 × 4 net screen pattern.
Dither Mode D
The scanner processes the 1 bit/pixel image by using 8 × 8 net screen pattern.
User Definition of Dither Modes A/B
In addition to the modes mentioned above, you can select two types of user-defined dither patterns to be
downloaded.
Note: When using halftoning mode, the image should be read at actual size, and then enlarged
or reduced to the desired size by using the zoom function.
This scanner also has the new function TET (Text Enhanced Technology), which allows the scanner
auto-adjust the threshold level to enhance monochrome reading.
Product Description GT-5000 / Action Scanner II Service Manual
1-22 Rev. A