Darker/whiter toggle for image opacity tool

Hi! First of all, thank you for this amazing tool!

Concerning the image opacity tool (https://omnitools.app/image-generic/change-opacity) I was expecting to obtain a "lighter" image by reducing the opacity value (like in Pixelmator on macOS) but I obtained the reverse: a lower opacity value gives a "darker" image.

Do you think that is possible to add a toggle to choose between a dark or a white opacity? (Or even more color?).

Thank you!

Examples below:

Original image:

Resulting image with omni-tools and 0,6 opacity:

Resulting image with Pixelmator and 60% opacity: