What is two-tone, how to comprehensively apply two-tone?

First of all, let's first understand what is two-tone, in fact, from its literal meaning alone can be understood, "two-tone" refers to the two colors, "tone" refers to the tone, that is, an image through the grayscale to separate out the dark part, light part and the middle tone, with One color to replace the dark part, another color to replace the light part, the middle call the transition color of these two colors instead. We use this picture to demonstrate, usually a normal color picture has three elements of color: hue, purity, brightness. If dealt with black and white or grayscale, which means that there is no hue and purity, just pure brightness performance, the picture is divided into the dark part, the light part and the transition zone in the middle. To replace the dark part first, a blue color is chosen, so the dark part of the picture becomes blue. A green is chosen for the light part, and now a two-tone effect is achieved, with the dark part of the picture becoming blue, the light part becoming green, and the gray part of the transition in the middle becoming a mixture between blue and green. If you reverse the process, replacing the darker colors with the brighter parts and the brighter colors with the darker parts, you will get this negative-like effect. Two-tone and two-tone difference in this "tone", here is not playing word games, indeed, because the two-color color scheme of the picture only two colors, and two-tone in addition to these two colors, there are transition colors between them. For example, if the two colors green and red are used together, there is no doubt that it is a two-tone color. But if the same green and red are used for two-tone color matching, it is green, red and the gradient between them. Take these two posters as an example, they use similar colors, but the one on the left is two-tone and the one on the right is two-tone. The dark and light part of the poster on the left is filled with these two colors respectively, and the middle tone part is the transition color between them, while the poster on the right only has these two colors. Now that gradients are mentioned, I'm sure some people will wonder what the difference is between a two-tone and a gradient. Again, we're still talking in pictures. Here we use this picture to demonstrate the gradient and two-tone effect respectively. The first step will be the first picture processed into black and white, the left side from bottom to top is a gradient of red to yellow-green, the right side is the use of these two colors of the two-tone effect. Gradient is equivalent to put a piece of tinted glass in the picture, this piece of glass is a gradient from red to green, the effect of looking through the glass is only an effect on the color, and will not change the details of the picture; and the right side of the two-tone effect is equivalent to give the picture a change of color, give a person a feeling of unreality, because this is the reality we do not see the effect of common. In fact, two-tone is not a product of design, as early as the late nineteenth century has existed, is the use of the camera to produce a two-tone effect. Originally appearing on sepia photographs, it is also one of the most commonly used two-tone colors. On the one hand, it was able to maintain the unretouched look of the industrial era, but on the other hand, it was also able to give the photograph an antique feel. This effect was later borrowed by the printing industry and became a cost-effective printing solution, as the use of two-tone coloring allowed for mass printing at a lower cost and added an artistic touch to the image. In recent years with the emergence of new media, the use of two-tone has gradually popularized, and more and more popular, the reason for popularity is no longer the problem of low printing costs, but more to do with the current aesthetic. The reason why two-tone can become a new trend, many people believe that the music platform "sound field" will bring this trend back to the mainstream, so when it comes to two-tone, most people's minds the first impression is this picture, but in fact, this is only a narrow sense of the two-tone, and the broader two-tone is not the only form of color matching. First of all, the first and most basic form is "black and white". Some people may say how can black and white be considered two-tone? Because here we are talking in a broad sense, as long as the effect can be achieved through the two-tone technique, it can be considered as two-tone, no matter what color it is. And black and white works can be achieved through the two-tone, but the fill color is black and white. But there is a point to remind you is that if you want to get a very textured black and white image, this also has to do with the photographic refinement and post-coloring, rather than simply two-tone can be achieved. "Black and colored". This form is also based on black and white, the dark part remains unchanged, and the light part is replaced with a colored one. This effect can be achieved with a gradient mapping technique or directly with a color block overlay. We use this picture to demonstrate, the method is to add a color block on the picture, filled with green, the layer mode selects the positive film overlay, can also be achieved by gradient mapping, the effect achieved are black and colored with the last with the text. "White and colored". This means that the dark parts are filled with a colored color and the light parts remain unchanged. This effect because the white is dominant, so there is usually a sense of lightness, simplicity, traditionally also called monochrome mode, but here we are given into the two-tone category. Still use this picture to demonstrate, the same superimposed color, but the layer mode to select the color filter, of course, can also be achieved through gradient mapping, the two methods to get the effect of although there are small differences, but negligible. "There is color and its different shades". In this form, the dark and light parts are replaced by the same hue, but the relationship between light and dark is expressed through the hue. "Colored and its different shades". This is the basic image we usually have of two-tone, and it is also the two-tone in the narrow sense we mentioned earlier. This form of two-tone with colored plus colored is difficult to achieve by overlaying color blocks; gradient mapping is preferred. Here we have done three different sets of two-tone colorways with this image. This series of posters is a visual image of a 100-member choir, the poster's production of creative use of classic paintings to depict the theme of the concert, the effect image, the background is the original paintings, and the poster is located on top of the original paintings to intercept the layout, respectively, with different color combinations of the two-tone processing, although each of the hue of a different, but because they are all two-tone presentation, so the overall look and is a whole. The visual image of this brand uses also colored and colored two-tone collocation, blue and pink combined together, giving people a young, fashionable feeling.