I'm completely new to image editing and visualizers but want to learn and have come across a problem I have no idea to address. I have a small picture that has an alpha/transparency layer and when I add it in front of an object to rotate a (slightly darker tinted) background becomes visible as it rotates. Any idea how to get rid of it? I just want the image to rotate without that effect. Hopefully I explained it right.
Thanks for any help.
Left side of sun
Screenshot 2020-09-07 195702.png (265.21 KiB) Viewed 3114 times
The problem is caused by alpha not being zero in the background of your small picture. It should be zero, but is just very low. This means that the transparency is not 100%, just close to it.
When the small picture's rectangular background overlays a bright area, its low alpha causes a small reduction in brightness. If alpha was truly zero (transparency 100%) there would be no brightness reduction.
A possible quick fix is to add the LumaKey module (Add > Effects2D > LumaKey) after your small picture to make dim areas truly transparent. Try Strength = 0.05, Falloff = 1.00 as initial settings. If strength is too high the dark areas of your wanted image will become transparent. In the unfortunate case that the wanted areas of your small image include regions that are truly black you won't be able to use LumaKey to fix the problem as some wanted areas are darker than some unwanted areas.
A less elegant alternative is to use a soft mask around the small image, fading it gradually to completely transparent outside the wanted area. Soft faint edges tend to disappear. A circular mask with a size to match your sun would be a good start. Scale and blur of the mask will interact, so if you change one you'll probably need to make small changes to the other for best results. See screenshot below.
To initially size/position the masking region, it's helpful to see where it overlays your background sun. Temporarily connect the signal that feeds the 2nd input of the mask module also to the first input of the Magic module and set the blur to 0.
If the small picture is an asset that you will be reusing a lot, consider processing it in a Photoshop-like app to make a truly transparent background.