Sharpening with precise Gaussian blur

[pierrelabreche]

Is there a Sharpen transformation that uses precise Gaussian blur with masking ?
What is recommended for making a transformation chain that combines sharpening based on precise Gaussian blur and quality upscaling ( resizing ) ?

[jsachs]

While there is no sharpening transformation that uses Precise Gaussian, Multipass Sharpening uses an edge-preserving blur algorithm that works well in most situations without having to create a mask.

If you want to both upscale and sharpen, you might want to take a look at Topaz Photo AI.

[tomczak]

I also think that between the Multipass and Advanced Sharpen - with all their options, edge 'spill barriers', and thresholds - you may have better luck with them in any sharpening, but just for fun you could try sharpening with masked Precise Gaussian Blur using e.g. this workflow:

1) Blur the areas that you want to eventually sharpen in the Original Image with the Precise Gaussian + Masks.

2) Blend in Offset Difference mode the Original Image with the blurred one in 1). The strength slider in this Blend instance controls the strength of sharpening. The output is effectively the High Pass part of the blurred areas of the Original Image with unblurred parts becoming solid 50% gray.

3) Blend again in Soft Light (or Hard Light) mode the Original Image with the High Pass output from 2) to sharpen.

You may need to separate the workflow into 3 branches to generate the intermediate images as the Blend operations are not commutative - i.e. it makes a difference which image is an input and which is an overlay.

[jsachs]

For the next release, I added an Increase Difference operation to the Blend and Composite transformations. If the overlay image is a blurred version of the input image, the output image will be a sharpened version of the input image, so you can use this to sharpen using Precise Gaussian. However, this technique will not have the halo suppression features built into the edge-preserving blur integral to Multipass Sharpen.

[pierrelabreche]

I also think that between the Multipass and Advanced Sharpen - with all their options, edge 'spill barriers', and thresholds - you may have better luck with them in any sharpening, but just for fun you could try sharpening with masked Precise Gaussian Blur using e.g. this workflow:
...

Thank you !

[tomczak]

In Transformations/Test Patterns, there is the Sharpen Test image. It helps me a lot to figure out what effect various settings may have on sharpening or blurring.

The image represents roughly all permutations of edge/background contrast, at 3 edge 'thicknesses' - kind of representing the 'roughness' of details to be sharpened.

Noting where and how edges are affected by a setting can be revealing as to what the algorithm does and how to take advantage of it when processing real images. It's probably the easiest to judge the effects of adjustments in the Show Difference mode in the Sharpen Control Previews.