Artificially specifying a color in CMYK with the help of the Color mixer the sum of whose components exceeds the limit of can lead to setoff on prints. Usually in the black point the total ink should not exceed this can be seen in the Info palette Total Ink. With the color separation settings shown above black should not fall below at the black point. Otherwise the shadows will be weak and the picture will be sluggish not enough contrast. Another important note avoid strong black point adjustments on individual channels. This can lead to an excessive decrease in the percentage of color inks and the black will become flat.
This is almost imperceptible on a monitor e-commerce photo editing especially a nonprofessional one but is very conspicuous when printed. At first glance working with curves in the RGB model is inconvenient it is not clear which of the R G B channels is responsible for the usual Cyan Magenta Yellow. There is no analogue to the Black channel at all. In addition when the content of red R decreases the content of green G and a little blue B also increases. But in fact there is nothing complicated in this model. If the direction of the RGB tone curve axes is set so that the shadows are on the bottom left and the highlights are on the top right then you can work with the curves in a similar way to the CMYK model.
At the same time Red corresponds to Cyan Green Magenta Blue Yellow this is clearly visible on the color wheel. It is easy to get used to this analogy since in all color correction procedures they are arranged in a similar order. Red Cyan Green Magenta Blue of the RGB model is that any point in the image can be seen on the overall RGB tone curve . This cannot be done in the CMYK model probably due to the presence of an ambiguity in the conversion from RGB to CMYK depending on the CMYK Setup color separation settings.