We and many others do personalized engraved gifts. The technique used is laser.

When engrave with laser on for an example a coated tumbler, the laser remove the coating (color) and the metal underneath is revealed.

You want an image to be 100% black to make sure that all coating is removed. This is no problem when it comes to texts etc but if you as a customer upload an image and have customily to convert it to black (image behavior) the result becomes negative.

To make this work, the image must be converted to a negative before converted to black (and remove background)

Would be great if Customily app could manage this step.

See image as an example.