CMYK color model of the primaries: cyan and yellow produce green, cyan and magenta produce blue, yellow and magenta produce red (these subtractive secondary colors correspond roughly to the additive primary colors), plus layering all three of them resulting in black. With halftoning, a full continuous range of colors can be produced. To improve print quality and reduce moiré patterns, the screen for each color is set at a different angle. While the angles depend on how many colors are used and the preference of the press operator, typical CMYK process printing uses any of the following screen angles: The "black" generated by
Combination printing often necessary to add artistic techniques to photographs. Discussing the benefits of composition in the art of photography and using combination printing, Robinson wrote, in "Pictorial Effect in Photography", that the method of combination served to "produce an agreeable presentation of forms and tones, to tell the story which is to be elucidated, and to embody the spirit of what it is intended the picture shall represent or suggest." His writings show his knowledge and his passion for creating new content in his photos with using this process. During the Victorian Era, another proponent of the technique of combination printing