Tone Distortion
Optical and physical phenomena in offset and flexographic printing cause printed halftone dots to render larger on paper substrates than on original press plates. The term dot gain expansion identifies this increase in tonal density caused by ink spreading into paper pores and light scattering within paper fibers. The boundary of this metric covers halftone screen areas from one percent to ninety-nine percent, stopping short of solid ink coverage where discrete dots merge completely.
Substrate Interaction
Mechanical spreading occurs during pressure transfer from blanket or plate to paper, while optical dot gain occurs when light enters the translucent substrate and scatters underneath ink film boundaries. Uncoated porous papers absorb liquid ink vehicle rapidly, causing higher mechanical spread compared to smooth coated paperboards. High surface roughness and elevated porosity increase both physical ink bleed and optical halation around dot perimeters.
A fifty percent target tint on plates often expands to sixty-five percent or higher on uncoated newsprint or recycled linerboard. Press operators adjust screen rulings and fountain solution levels to restrict unwanted dot growth during production runs.
Curve Compensation
Prepress technicians build compensation curves into raster image processors to reduce platemaking dot sizes prior to printing. Corrective curves lower nominal file percentages so that printed sheets match target color proofs. Accurate compensation prevents muddy midtones and loss of shadow detail in fine graphic reproductions.
