P: Simulating a center-radiating "linear" gradient

[robkendrew]

Is there any way in LrC to create a linear gradient that radiates out equally from the centre rather than always graduating from the top or bottom?

ON1 Photo RAW has this feature and it was a really useful way to accurately mask a section of the image. I suppose one could replicate it with a very large flat radial gradient but I wondered if there was a keyboard modifier that did this to the LR linear gradient that I'm missing or is this something for the next upgrade?

[JohanElzenga]

No, but what you want does indeed sound like an image-wide radial filter.

[johnrellis]

"I suppose one could replicate it with a very large flat radial gradient"

It's not clear to me how what you're describing differs from a radial-gradient mask?  Are you asking for a quick way to create a radial gradient that's perfectly centered in the photo extending to the edges?  I've attached a preset Centered Radial Gradient that does that.

[Rikk Flohr: Photography]

I think they are looking for something like this, or it's inverse, but in a single 'drag' application.

 

[JohanElzenga]

Maybe (and that is easy to do as well), but that does not "equally radiates out". It only does to the top and the bottom.

[johnrellis · Accepted solution]

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"a linear gradient that radiates out equally from the centre rather than always graduating from the top or bottom"

Here's a preset Symmetric Linear Gradient that implements Rikk's interpretation (which makes most sense to me now):

It's flat to 6 parts out of 10,000 (0.06%).

[robkendrew]

Perfect! This is exactly what I'm after. Thank you!

[Suzanne Mathia]

Brilliant!

[Rikk Flohr: Photography]

@johnrellis  I've been doing this adjustment as a preset for years. I originally built as series of these to simulate the Singh Ray Reverse Graduated filters. Editing the preset by hand allows you to be very precise in your transition between the two constituent linear gradients.  https://singh-ray.com/equipment-technique/nd-filters/the-reverse-graduated-nd-filter/  

[johnrellis]

@Rikk Flohr: Photography, the Symmetric Linear Gradient preset I posted shouldn't require manual editing. You can drag it anywhere and independently adjust the inner lines (where the preset starts to fade out) and the outer lines (where the preset completely fades out). 

I uses a very wide radial gradient that is very nearly linear (6 pixels out of 10,000). It took some careful discovery of the parameters of that gradient, since the LR/ACR rendering engine fails to render extremely wide radial gradients.

[Suzanne Mathia]

Love to know how you created this.

[johnrellis]

"Love to know how you created this."

I saved a radial gradient as a preset and manually edited these fields in the preset's .xmp file:

crs:Top="0.35"
crs:Left="-9.5"
crs:Bottom="0.65"
crs:Right="10.5"
crs:Angle="0"
crs:Midpoint="50"

That makes a radial gradient that's 30% the height of the image and 20 times the width of the image. The top and the bottom lines of the gradient are very nearly flat at that width.

You can make such a mask in Develop by continually dragging the radial to the left and then extending its right edge, but it's quite tedious to do it that way.