The basic principles of CTP Plate continuous-tone image reproduction
Jul 20, 2026
The Basic Principles of CTP Printing Plate Continuous-tone Image Reproduction
In the shadow areas of an image, the recessed cells are deeper and contain a thicker ink layer; in the highlight areas, the recessed cells are shallower and carry a thinner ink layer. The continuous variation in ink film thickness enables the reproduction of different tonal levels and densities of the original image.
By utilizing dot coverage (also known as ink coverage area ratio), the ink coverage on the substrate can be adjusted through the screening process, thereby reproducing continuous tones. This principle is known as tone reproduction through halftoning.
Screening technologies can generally be divided into two major categories:
AM Screening (Amplitude Modulation Screening)
FM Screening (Frequency Modulation Screening)
In printed images, the spacing between halftone dots remains constant, while the dot size is changed to control the ink coverage ratio within a unit area.
In the highlight areas of an image:
Smaller halftone dots are generated.
The surrounding non-image areas are relatively larger.
The total dot area within a unit area is smaller.
Ink coverage is lower.
More light is reflected and less light is absorbed.
Therefore, the printed area appears brighter.
In the shadow areas of an image:
Larger halftone dots are generated.
The surrounding non-image areas become smaller.
The total dot area within a unit area increases.
Ink coverage becomes higher.
Less light is reflected and more light is absorbed.
Therefore, the printed area appears darker.
