These are all the possible values for the IG_ISIS_TAG_BRIGHTNESS tag.
Values:
| IG_ISIS_BRIGHTNESS_AUTO | Set brightness value automatically based on real-time sampling during scanning. |
| IG_ISIS_BRIGHTNESS_DARKEN | Lighten the page relative to IG_ISIS_BRIGHTNESS_NORM. |
| IG_ISIS_BRIGHTNESS_NORM | Select a "normal" brightness. |
| IG_ISIS_BRIGHTNESS_LIGHTEN | Darken the page relative to IG_ISIS_BRIGHTNESS_NORM. |