Dot is the basic printing unit of continuous tone image. By comparing this image unit with the blank on printed matter, the effect of continuous tone reproduction can be achieved. The point in PS is the value of CMYK color at a certain point. By adding a single color or weakening some colors, you can achieve the desired effect of printed matter. If you want to add some colors, you can use the color balance in PS to add colors. If you just mix colors evenly, the curve should be fine. If you want to adjust one part without affecting other parts, you need to use pen tool, magic wand and lasso tool to select the part to be adjusted. The edge must be feathered and then adjusted.