Normal Jpeg files contain red, green and blue information. There is another file type called PNG. This
filetpe contains red, green, blue and alpha information. The alpha channel determins how transparent the image is.
The 3D gray system uses this information to set the background to black for the maximum output when the transparency is 100%.
The parts of the image that are not transparent are then dithered with the selected dither method.
So how do we create these PNG files? You can use a photo editor like photoshop and erase parts of the image by hand and then save
the image as a PNG file or you can use Green Screen Wizard to use a photo with a green background and output a transparent background with
the click of a button.
In Green Screen Wizard, first load an image with a green background:
Then select output transparent background. Where the checkerboard shows that is the transparent area.
Then click on the save button. The Wizard will know you need a png file as it has a transparent background.