How does the opacity value work?

I am using StretchImage to put a bitmap on the display and there is a parameter on the end called Opacity.

The Microsoft website says this about it.

The bitmap’s degree of opacity. A value of 0 (zero) makes the bitmap completely opaque (not transparent at all); a value of 255 makes the bitmap completely transparent.

If I use 0, nothing is shown. If I use 255, I see the bitmap but the there is a shadow left by something that is drawn in black on a white background. It’s a bit like a burn in effect but it is clearly not that. Pausing the display update and the shadow remains.

Any other value in between and it gets worst for the shadow effect.


This sounds like an issue of setting the opacity of the bitmap without having something else in the background to overlay on top of. While the values seem to work opposite of what Microsoft claims in the API reference, I would try adding an image to a bitmap, and drawing my second image on top of that with the opacity setting, and see if the behavior is the same or not.