What is Halftone Screen Raster?

What is Halftone Screen raster for screen printing in Photoshop?

In Photoshop there are 5 methods provided, namely, 50% Threshold, Pattern Dither, Diffusion Dither, Halftone Screen, and Custom Pattern. The following is an explanation of Halftone Screen to better understand the process of making films for screen printing. 

Halftone is a reprographic technique that simulates a continuous tonne image through points varying in size, shape or distance. Halftones can also be used to specifically refer to the resulting image. 

Where a continuous color ton image contains unlimited colors or grays, the halftone process reduces visual reproduction for binary images printed with only one color of ink (binary is a writing system that uses only two symbols namely 0 and 1). This binary reproduction depends on the basic optical illusion that these tiny halftone dots are mixed into subtle tones by the human eye. At the microscopic level, black-and-white photographic films were developed which also consisted of only two colors, and not a range of tons that continued indefinitely. 

Just as color photography evolved with the addition of filters and film layers, this printing is made possible by repeating the halftone process for each subtractive color the most common use of this is in the CMYK printing method. This ink's semi-optical property allows halftones with dots of different colors to create another optically colorful image effect. 

Three examples of halving colors using the CMYK system. From left to right. Cyan separation, magenta separation, yellow separation, and black separation. The combined halftone pattern and finally how the human eye sees the combined halftone pattern from a considerable distance (far right). 

Although round dots are the most commonly used, there are other types of points available, each with different characteristics. And they can also be used together to avoid the moire effect. Generally, the most preferred dot (round) shape is included in the world of screen printing or printing, but it depends on the printing equipment as well. 

There are 3 types of points(dot): 

Spin point: this is the most common, suitable for images that focus light images, especially for skin tones. They meet at a pitch value of 70%. 

Ellipse point: this is suitable for images with many objects. The points of the ellipse meet at the values ​​of 40% (end pointing) and 60% (long side), so there is a pattern risk. 

Square dots: best for detailed images, not recommended for skin tones. These angles meet at a tonal value of 50%. Transitions between square points can sometimes be seen with the human eye