In your print environment, you may not be overly concerned about absolute press gain or loss—only with relative gain or loss. You may just want to make a given ink print lighter or darker at a given tone (for example, reduce dot gain by 2% at the 50% point).
The aim is to make a curve that makes a slight adjustment to make the output darker or lighter. You have a choice of making a transfer curve or a calibration curve.

Disadvantages of transfer curves

It might appear that the simplest approach would be to create transfer curves for the following reasons:

• You may not have actual current or target data to work from
• You might wish to avoid the effort of having to create three different curves just to end up with one usable curve.

However, you should not use transfer curves, even though the process appears to be less work. There are two main disadvantages of using transfer curves:

• Deviation mode is used to establish transfer curves. This means that after the deviation is applied, the displayed deviation value resets itself to 0% at the correction points, and you have no indication of how much correction was originally applied. For example, you could subtract –2% at the 50% point, and after the correction is applied, you can see visually that the curve dips down at 50%, but you have no way of knowing how much adjustment was applied. Unfortunately, with a transfer curve you have no way of determining the exact correction, because after application, deviation values are reset to 0%.
• If there is a global change in press conditions, you have no way of automatically updating all of your curves to compensate for this change. You must open every transfer curve and manually correct for the changes in current press conditions.

Advantages of calibration curves

There are two advantages to using derived calibration curves instead of transfer curves.

• You have a database that allows you to see what corrections have been applied.
• You have a simple mechanism to make global changes to all curves, if print conditions change.

Optimizing your workflow to create and modify derived calibration curves will be discussed later on in this chapter.