Optical Blur
Characterization of light scattering within a paper or coating layer is essential for predicting the resolution of printed graphics. The point spread function describes how an infinitely thin beam of light spreads out as it passes through or reflects from a substrate. This mathematical function defines the limits of optical print sharpness.
Image Distortion
As light enters the fibrous matrix of the paper, it scatters off the cellulose fibers and mineral pigment particles, creating a blurred halo around the original point of entry. This blurring reduces the contrast of the printed image because the dark dots appear to bleed into the white spaces. This effect is especially noticeable in fine halftone screens, where it can cause the highlights to look muddy and reduce the overall detail.
Minimizing this spread is crucial for high-speed digital printing.
Quality Assessment
Calculation of this function is performed by projecting a high-contrast line or slit onto the paper surface and measuring the intensity profile of the reflected light with a high-resolution sensor. The width of this profile reveals the scattering behavior of the paper, allowing researchers to evaluate the performance of different coating formulations. Paperboard mills use this information to optimize the thickness and pigment blend of their coating layers, with the goal of reducing the lateral travel of light.
This optimization ensures that high-speed packaging lines can produce barcodes and text that are clean and easily readable by optical scanners.
