One technological breakthrough in printing photos in magazines was the _________________, pioneered by Frederick Ives in the 187
0s and 1880s. He found a way to divide a photograph into a microscopic grid of raised dots. Depending on whether they were bigger or smaller, close together or farther apart, the dots would resemble the original photograph.
The technological breakthrough mentioned in the question is the halftone printing method used for the printing of photographs. The technique took advantage of dotting when printing the photos. Instead of using continuous lines, they used dots that differed either in size or tones of black which from a distance, was not observable and looked like a regular photograph but it helped cut down the amount of ink used greatly.
