Using transfer function to compensate for dot correction in film

When using a CMYK color profile, you cannot customize the dot correction settings. However, it is possible to compensate the dot correction by a mis-aligned imagesetter through a transfer function.

The transfer function compensates for dot corrections between images and film. For example, the transfer function makes 50% dots in the image print as 50% dots on the film. Similar to the dot correction curve, the transfer function can specify up to 13 values ​​along the grayscale to create a custom transfer function. Unlike the dot correction curve, the transfer function is only suitable for printing - they do not affect the image's color data.

Use the following principles to determine the best way to solve network point corrections:

If you are using a custom CMYK profile, use the dot correction settings in the custom CMYK dialog box to adjust the dot correction to match the print effect.
If you are using an ICC profile and the dot correction value does not match the printing effect, try to get a new profile with a matching value.
The transfer function is only used when the first two methods are not options.
To adjust the transfer function value:

Density values ​​are recorded using a projected densitometer on the film image with appropriate steps.
Choose File > Print Preview.
Select "Show other options" and choose "Output" from the pop-up menu.
Click the "Transfer" button.
Calculate the desired adjustment and enter the value (in percentage) in the Transfer Function dialog box.
For example, if 50% of the dots are specified and the imagesetter prints it at 58%, the halftone has an 8% dot correction. To compensate for this correction, enter 42% (50% - 8%) in the 50% text box in the Transfer Function dialog box. The imagesetter then prints the 50% of your desired dot.

When entering the transfer function value, remember the imager's density range. On a given imagesetter, a small high-gloss dot may be too small to allow ink to adhere. When a certain density level is exceeded, the shaded dot may be filled with pure black and all details of the shaded area will be lost.

Note: To retain the transfer function of the exported EPS file, select Override Printer Default Function in the Transfer Function dialog box, then select Include Transfer Function from the EPS Format dialog and export the file. (See Storing Files in Photoshop EPS Format (Photoshop).)

To save the current transfer function settings as default:

Hold down Alt (Windows) or Option (Mac OS) to change the Store button to> "Default" and click this button.

To load the default transfer function settings:

Hold down Alt (Windows) or Option (Mac OS) to change the Load button to <From Default and click this button.

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