I have done this job many times, and the adjustment process of each painting is different. As you said, "The background color of the work is very heavy, the brightness is inconsistent from top to bottom, and sometimes the color cast is very strong." When retouching, we need to deal with the specific situation, especially to take care of the overall effect of the whole painting (as close as possible to the normal color effect of Chinese painting, Chinese painting and PS skills are difficult to be familiar with; So it is impossible to write a fixed retouching method.