Limit object view bounds, or better blur technique in Sketch

Question

Using Sketch, I'm trying to duplicate the blur approach used in this image (source):

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But I can't figure out how to blur properly in Sketch. The closest approach I could find was using background blur.

Instead of a constant blur, I end up with blurred white sides like this, when my result should look like this accidental result that I cannot replicate.

Right now the 2 fixes I see for this are:

• Find a better way to blur in Sketch
• Figure out a way to limit the view bounds of a single object, similar to crop, but it's more of a "view boundary mask"

I am definitely open to other approaches.

Answer 1

My approach to solve this problem:

1. Place layer above your image. Add gradient fill with same color at ends (#000000) set 0% alpha on one endpoint and 100% alfa on another. Make point of gradient be at same place as on picture below. Make this layer as Alpha Mask () Ctrl + ⌘ + M.

2. Add empty layer bigger than layer mask, this will remove white borders. Apply background blur 6px on this layer. This layer is the masked one by the alpha blur layer.

Download sample Sketch file.

Good article on this technique.