6. Compensate dot gain with transfer function If the image output device used is improperly calibrated, the dot gain or shrink may occur when the image is transferred to the film. This can be done using the POSTscript transfer function (TRAnSFER FunCTIOn). Compensate. In addition, a transfer function can also be used when it is intended to precisely control the dot gain of different gradation regions of the image.
7. Difference between transfer function and dot gain curve The transfer function is easily confused with the dot gain (DOT GAIn) curve in the color separation parameter setting dialog box. The dot gain curve in the color separation parameter setting is to compensate for the dot gain generated after the printing process conditions, and the transfer function is to compensate for the dot gain generated when outputting the color separation film, that is, the former is suitable for the printing process, and the latter It is used for the platemaking stage. 
8. Compensate dot gain with transfer function Click on the TRAnSFER button in the PAGE SETuP dialog box in PHOTOSHOP to enter the TRAnSFER FunCTIOnS dialog box; calculate the required adjustments and enter them in the appropriate boxes (in percent). For example, if the pixel value is 127, it should have been output as a 50% dot, but the imagesetter will output 58% of the dots, thus knowing that the midtones have an 8% dot gain. In order to compensate for this dot gain, enter 42% (50% to 8%) in the 50% text box of the dialog box. The imagesetter will then output the 50% dots that the user wants. In this correction the image information does not change, but the transfer function is embedded in the file for the RIP software to compensate for the dot gain at output. The transfer function allows the user to define 13 values ​​along the grayscale direction of the image's dominant color channel, creating a custom transfer function curve. As shown in Figure 4, PHOTOSHOP allows the transfer function curve to be defined for each color version. Of course, this is actually an enlargement curve of the photosetter's dot. When entering the transfer function value, keep in mind the density range of the final output device (printer) of the image used. A small high-gloss dot can be generated on a high-precision photo-composing machine, but for a printing press, a small high-gloss dot may be too small to hold ink; in addition, such a small dot may be in the print Lost. Similarly, if a certain density range is exceeded, dark screen dots may fill in the field at the time of printing, thereby losing the details of the dark tone area.
Figure 3 Compensating dot gains using map curves Figure 4 Using transfer function to compensate for dot gains It should be emphasized that:
1 The pressure of digital printing is less than that of traditional printing. In the case of color separation for digital printing, DOT GAIn should be distinguished from general printing.
2 Although 80% or 90% of outlets will increase to 100% after printing. But this is inconsistent with the effect produced when 100% of the dots are printed.
80% of the outlets only reach the field density in 80% of the dot areas, while the expanded 20% have ink, but the ink is thin and the density cannot reach the density in the field. Therefore, 80% of the outlets are not visually 100% of the outlets are thick and bright, so the place where 100% outlets are used must not be ignored. The increase in outlets is an objective fact. The result is that it is difficult to obtain the ideal outlet size on printed matter. For this reason, it is necessary to compensate for dot gains during pre-press computer design and color separation, so as to increase the dot-size increase rule to the required size during printing. (Finish)
7. Difference between transfer function and dot gain curve The transfer function is easily confused with the dot gain (DOT GAIn) curve in the color separation parameter setting dialog box. The dot gain curve in the color separation parameter setting is to compensate for the dot gain generated after the printing process conditions, and the transfer function is to compensate for the dot gain generated when outputting the color separation film, that is, the former is suitable for the printing process, and the latter It is used for the platemaking stage. 
8. Compensate dot gain with transfer function Click on the TRAnSFER button in the PAGE SETuP dialog box in PHOTOSHOP to enter the TRAnSFER FunCTIOnS dialog box; calculate the required adjustments and enter them in the appropriate boxes (in percent). For example, if the pixel value is 127, it should have been output as a 50% dot, but the imagesetter will output 58% of the dots, thus knowing that the midtones have an 8% dot gain. In order to compensate for this dot gain, enter 42% (50% to 8%) in the 50% text box of the dialog box. The imagesetter will then output the 50% dots that the user wants. In this correction the image information does not change, but the transfer function is embedded in the file for the RIP software to compensate for the dot gain at output. The transfer function allows the user to define 13 values ​​along the grayscale direction of the image's dominant color channel, creating a custom transfer function curve. As shown in Figure 4, PHOTOSHOP allows the transfer function curve to be defined for each color version. Of course, this is actually an enlargement curve of the photosetter's dot. When entering the transfer function value, keep in mind the density range of the final output device (printer) of the image used. A small high-gloss dot can be generated on a high-precision photo-composing machine, but for a printing press, a small high-gloss dot may be too small to hold ink; in addition, such a small dot may be in the print Lost. Similarly, if a certain density range is exceeded, dark screen dots may fill in the field at the time of printing, thereby losing the details of the dark tone area.
Figure 3 Compensating dot gains using map curves Figure 4 Using transfer function to compensate for dot gains It should be emphasized that:
1 The pressure of digital printing is less than that of traditional printing. In the case of color separation for digital printing, DOT GAIn should be distinguished from general printing.
2 Although 80% or 90% of outlets will increase to 100% after printing. But this is inconsistent with the effect produced when 100% of the dots are printed.
80% of the outlets only reach the field density in 80% of the dot areas, while the expanded 20% have ink, but the ink is thin and the density cannot reach the density in the field. Therefore, 80% of the outlets are not visually 100% of the outlets are thick and bright, so the place where 100% outlets are used must not be ignored. The increase in outlets is an objective fact. The result is that it is difficult to obtain the ideal outlet size on printed matter. For this reason, it is necessary to compensate for dot gains during pre-press computer design and color separation, so as to increase the dot-size increase rule to the required size during printing. (Finish)