Digital Halftone Image Definition and Characteristics

We are probably familiar with the general workflow of laser printers and even imagesetters. These machines place dots on a piece of paper or film in a pattern that is less obvious than the organization, shape of the dots, and the frequency at which the dots are arranged in a straight line at different angles.

Digital halftone image

A continuous-tone image such as a photo has a range (color or hue width) that is very close to the color or tonal range that the human eye can perceive so that we cannot see the color or tone band in the photo. Distribution (that is, there is a color boundary between transition shadows). In other words, the hue in the continuous tone image is continuous, and they neither start nor end for the colors that make up the shadow. Photoshop's gradient fill is a good visual example where the design elements exhibit continuous tone characteristics. In contrast, we can clearly see in Neapolitan ice cream where the chocolate ends and where the vanilla begins. As long as ice cream does not melt, they will not show the characteristics of continuous tone.

The color range of the black-and-white print material is limited by the foreground color and the background color. To express the luminance value in the grayscale image, the meshes of various sizes must be arranged in a precise pattern so that they are exactly the same as they are represented in the original image. The value of the corresponding. A Postscript-printed image, next to it is a PCL-printed image. It can be seen that the dot size in Postscript replicas varies, but is exactly the same in appearance. Its quality is not only good enough to give to partners or customers, but also has invaluable value in business printing.

It is well illustrated how Postscript dots correspond to their tone equivalents in digital images. It can be seen that about 50% of the black area in the original image is represented in the Postscript print result by halftone cells occupying half of the "white space." Every dot that the viewer sees is a digital halftone cell that is located in a grid that is invisible but accommodates all halftone dots.

Let's do a little experiment: Hold the book by hand and place it four feet away from you. Then observe the halftone image in the previous image, and observe the PCL and error diffusion image in the same way. . Readers will notice that the consistency of dot shapes, sizes, and organization (called line screens) is such that an observer can easily interpret what he sees as a button image. This is the main difference between halftone screening technology and other technologies.