Field/Iris blur bug?

Question

If I create a generic solid black shape on a new transparent layer, and then apply say 20px field blur and 20px iris blur, then I start to see a white glow from the object. (no bokeh is on by the way)
It's as if photoshop is pretending as if the shape is on a white layer instead of a transparent one.
Is this a bug or am I misunderstanding what field blur and iris blur actually do?

Answer 1

anistropic wrote:
It's as if photoshop is pretending as if the shape is on a white layer instead of a transparent one.
The raster shape really is surrounded by white fully transparent pixels and the Blur Gallery filter is blending the white with the colour of the shape.
After you initially create the shape pixel layer, do Layer > Layer Mask > From Transparency to make the pixels fully opaque and extract the transparency into a mask. Disable the mask to see the white surrounding the shape. Fill the entire layer with the shape's colour. Enable the mask or apply the mask to make coloured fully transparent pixels. Now the Blur Gallery will not make a white halo.
Realize that if you apply a mask rather than just enable it, and save the document, then the next time Photoshop opens the document, the fully transparent pixels will contain white.
Is this a bug or am I misunderstanding what field blur and iris blur actually do?
You are not misunderstanding these filters. The Gaussian Blur filter, for example, cleverly avoids the white halo problem, so hopefully the developers will implement a similar improvement to the Blur Gallery.