The implementation method of original color classification in sample printing is that the original is usually divided into CMYK four colors. If it is a color drawing or color photo, it is almost difficult to select the color on thousands of pictures. Therefore, the four-color printing method is usually used. That is, the original is color decomposed, divided into four-color (CMYK) color plates before printing, and the color is synthesized in the process. The traditional "color separation" is mainly a color separation process based on the principle of subtraction through the selection and absorption characteristics of different wavelengths of color. In this way, the color is filtered to form supplementary light, so that the photosensitive film forms a negative film of black-and-white image, and then screening to form a dot.

由于企业的大量应用，现代印刷技术已经不再使用上述的分色方法，现在我们通过印前扫描、取样转化的数字化技术，将原稿分解为RGB三色，通过电脑的数字化计算处理为CMYK即可实现分色。

Due to the extensive application of enterprises, the above color separation methods are no longer used in modern printing technology. Now we decompose the original into RGB three colors through the digital technology of prepress scanning and sampling transformation, and realize color separation by computer digital calculation and processing into CMYK.

图像加网的原因与优势，印刷设备的固态确定决定了印刷只能采用网点再现原稿的连续调层次。如果我们有经验会发现，图像放大若干，发现其是由大量的网点组成的图案形象。

The reasons and advantages of image screening, the solid-state determination of printing equipment determines that printing can only use dot to reproduce the continuous tone level of the original. If we have experience, we will find that the image is a pattern image composed of a large number of dots.

因其占据同等大小的空间位置，尽管图像网点大小不一定一样大，为了避免这样的工艺缺陷，我们通过对原稿图像加网，通过网点中圆点大小来表示图像颜色的深浅。

Because it occupies a space position of the same size, although the image dot size is not necessarily the same, in order to avoid such process defects, we screen the original image and express the color depth of the image through the dot size in the dot.

网点的空间位置和网点大小决定了产品的层次感，当挂网数量更高，网点所占据的空间位置则越小，反之所占据的位置就越大，所能描述的层次就会减少，印刷成品就越粗糙。事实上，印务前原稿的色彩与层次都是通过这样的形式挂网后被再现出来的。

The spatial position and size of the outlets determine the sense of hierarchy of the product. When the number of screens is higher, the smaller the spatial position occupied by the outlets. On the contrary, the larger the position occupied, the fewer levels that can be described, and the coarser the printed products. In fact, the color and level of the original before printing are reproduced after hanging the net in this form.