1. How Changing Dot Size Makes Our Eyes See Dark and Light Shades
When you examine a newspaper photo with a magnifying glass, you see black dots packed closely together. In the dark parts of the photo, the dots are large. In the light parts, the dots are small. The ink itself is not diluted; its color remains the same. Instead, traditional halftone printing changes the size of the dots, and in some methods, the spacing between them, to show different shades [6].
If the dots are small enough, the human eye receives the collection of dots as a smooth gradient of light and dark. This trick uses the way our eyes perceive clusters of dots as shades. This method is called halftone. But who first thought of this idea, and when?
2. How the Halftone Idea Took About 30 Years to Become a Business
The concept of halftone is said to have started in 1852, when William Fox Talbot in Britain proposed using a "screen" or "veil" for photographs in a patent. Talbot is known for his work in photography [6].
About 30 years later, in 1882, Georg Meisenbach in Germany patented a method called autotype. He is said to be the first person to achieve commercial success with halftone plates for letterpress printing, where ink is applied to raised parts of the plate. Other methods, like Frederick Ives’ patent in 1881, also existed [6].
Later, brothers Lewis and Max Levy, along with Frederick Ives, created high-quality cross-line screens. This history shows that it took about 30 years and the efforts of many people to turn the initial idea into a usable form. How, then, do we print colored photos using dots?
3. How Color Printing Layers Four Ink Colors of Dots at Different Angles
In color printing, many colors are created by changing the density of dots in four colors: Cyan (blue-green), Magenta (red-purple), Yellow, and Black (CMYK) [6].
However, if the grids of these four colors are aligned in the same direction, interference patterns called moiré can appear. To prevent this, the angle of the halftone dots is changed for each color. This causes the dots to arrange themselves into small rosette shapes. The combinations of angles used in the printing industry are standardized [6].
Even when four colors of fine dots are layered, the eye sees one image. Behind this is the careful work of shifting the angles. Now, let us look at the "plate" needed to put these dots on paper.
4. How Lithography Prints Using Water and Oil Without Carving
In lithography, one draws on a limestone surface using ink or crayons that contain fat. The stone is wetted with water, and then oily ink is applied. The ink sticks only to the drawn parts because water and oil repel each other [1].
The surface of the plate is flat, not carved. This is called planographic printing. Because the drawing is not carved, it transfers to the paper as it was drawn. It is said that lithography spread worldwide because it did not require the labor and skill of carving, and because it could express fine detail and rich shading [4].
Alois Senefelder in Germany is credited with inventing it. Some sources say he conceived it in 1796, while others say he completed it in 1798. The two dates may refer to two stages, conceiving the idea and completing it [2].
In Japan, a record shows that a Prussian (part of modern Germany) envoy presented a lithographic press to the shogunate in 1860. Lithographs were made from the end of the Edo period. The Meiji 10s and 20s (roughly 1877 to 1896) are described as the era of lithography [2]. However, using heavy stone plates is difficult. How did this change?
5. How an Accident with Rubber Led to Offset Printing
Most modern printing uses offset printing. Instead of printing directly from the plate to the paper, the image is first transferred to a rubber blanket, and then to the paper. This is an indirect method [5].
The origin is said to be an accident in 1904 by Ira Rubel in the United States. When a machine was run without paper, the ink from the plate printed onto the rubber blanket. The next sheet of paper inserted picked up that image on its back. Accounts vary slightly: some say paper was forgotten, while others say a worker ran the machine without paper [5].
Using rubber allows fine printing on rough paper, suits color printing, and allows for fast speeds. Therefore, it is widely used for posters, magazines, newspapers, and books [5].
The evolution from lithography is visible. In the mid-19th century, cylinder printing presses were made. The plate material changed from stone to zinc and aluminum, leading to modern offset printing. The water-and-oil principle of lithography continues in offset printing [3]. Is there a way to print directly from data to paper without making a plate?
6. How Inkjet Printing Started with a Hot Soldering Iron
Many household printers use inkjet technology. They do not use a plate; instead, they shoot tiny drops of ink directly onto the paper.
The origin was an event during Canon’s research. A hot soldering iron accidentally touched the needle of a syringe filled with ink. Drops of ink shot out forcefully from the tip. Using this as a hint, Canon filed a basic patent for the bubble jet method, which uses heat to eject ink, in 1977. The first product, the BJ-80, was released in 1985 [7].
In the thermal method, an electric current heats a small chamber rapidly. This evaporates the ink to create a bubble. The force of the bubble pushes the drop out of the nozzle. Another method uses piezoelectric elements, which bend when voltage is applied, to push out ink [8].
The size of the drops from the nozzle varies by model, ranging from a few picoliters to over 50 picoliters. One picoliter is about one trillionth of a liter [8]. Around the same time, researchers at HP were separately developing a method to eject drops using heat from the resistance of a thin film. Inkjet technology grew from similar ideas developing at the same time in different places [8].
7. How to Find Printed Dots in Things Around You
Try looking at photos in newspapers or flyers at home with a magnifying glass. Compare how the dot sizes differ between dark and light areas. If it is a color photo, try to look for the direction of the dots for each color.
If you have an inkjet printer at home, you might print a similar photo and compare it. The arrangement of dots might be different. If you want to read more, you can look at Canon’s history of intellectual property [7] or the Japan Printing Industry Association’s Printpia [3].