Epson Perfection 640U Reference Manual page 59

Tone Curve Name list:
Select a tone correction setting from this list. The custom settings
you have saved appear in this list.
Tone Curve editor:
The editor allows you to customize tone correction. Drag points
on the tone curve to adjust the tone value. You can edit up to five
tonal elements.
Output options:
If you select the check box for a specific point, such as 1/4 Tone
or Midtone, you can move that point and it remains where you
leave it; it is not affected by the movement of other points on the
curve. If the check box is cleared, the point becomes affected by
the movement of other points.
Channels options:
You can select the combined red, green, and blue (RGB) channel
to modify all colors, or select these colors separately.
Note:
If Image Type is set to Black & White Photo or Black & White
Document, you can only select the combined RGB channel option.
Save/Delete/OK/Cancel/Help buttons:
After you correct tone, type a name for your custom settings in
the Tone Curve Name list, and then click Save.
To delete a setting, select the name of the setting you want from
the Tone Curve Name list, and then click Delete.
To accept the defining Tone Correction or close the dialog box,
click OK.
To cancel the operation, click Cancel.
Understanding EPSON TWAIN Features
3-13