Alpha mask in Twilightrender 2

[RichH]

Is the alpha mask feature working properly?

I used a PNG file to make a FaceMe Tree component in SketchUp 2015. I placed two of them onto a face with grass texture and rendered an eye level view at a Low 800x600 resolution. I saved a PNG of that render. I then rendered an Alpha Mask of the same view and saved that PNG . I applied the Alpha mask PNG as a clipping mask to the full render PNG in two programs. Putting a black rectangle behind the clipped image shows quite an extensive "halo" of white around the perimeter of the "trees." This is much more visible than it is in the original PNG file. I've illustrated it in the image below.

This type of stuff also happened at the 05+ and 07+ presets with 3200x1600 images.

[Chris]

It is recommended that you render your alpha mask at double the render size of your production render. Then in your post-production tool (photoshop, gimp) resize the mask by 1/2 to use in masking your image. This helps reduce edge artifacts.

If that doesn't work well enough, I recommend that you render your image with a background in SketchUp as close in color to your final background as possible. Because anti-aliasing will cause some blurring of the edges of objects with the rendered background (that's just unavoidable), there will probably always be a small amount of color-cast along edges. Best to try to match it to your intended background as close as possible.