Gaussian Blur Export to Tiff - correct amount not applied

[GFS]

I have a gaussian blur layer, which when exported to tiff, is not applied to the same level (amount) as the screen preview in AFP 1.7.3.

In order to have the same amount of blur in the exported tiff, I have to increase the blur radius from 0.9 to 3.8px 

[walt.farrell]

When you previewed it in 1.7.3, were you at 100% zoom? If not, perhaps the on-screen rendering of the blur was not accurate.

[GFS]

Thanks Walt.

You're correct.. and there I was thinking that zoom to 100% to see if, e.g. banding is really there, days we're over.  Ho hum.

*However*

This remains an issue.  I need to be able to see my entire image on-screen, in order to judge how much blur I want to apply.  Zooming in to 100% on a ~100 megapixel image is completely unworkable in this regard.

So at the moment, in order to see how much blur I want, I have to make a guess in AFP, Export to tiff, look at that, go back, adjust, Export to tiff, look at that, go back adjust, Export to tiff, look at that ... I think we call this a problem.  The AFP preview (on-screen image)  needs to be accurate.

[GFS]

I wonder if this isn't a decision about speed by Serif.  I expect that AFP has a pyramid of internal jpegs for display and adjusts on the fly for in-betweens.  Blur is slow to calculate and can bring AFP to it's knees in processing ... although this has improved significantly with 1.7x.  Perhaps it would be enough to simply offer a checkbox to use 'accurate' previews, when desired.  My old favourite imaging app had this waaaayyy back in the mid90s.  A simple toggle between speed and accuracy.

[walt.farrell]

2 hours ago, GFS said:

A simple toggle between speed and accuracy.

You could create a feature request for that; it does sound useful.

[Chris B]

Hi GFS,

This is just the way we render what's on-screen and is called mipmapping. I appreciate what you're saying so feel free to make the feature request in the correct forum. 

[GFS]

Thank you Chris B.

Can you tell me what the advantages of mipmapping are in this respect?  Is it just a question of speed?

[Chris B]

It's just the way we render the screen. At 100% view, the image and screen pixels match 1:1. When you view the image less than 100%, the image must be resampled which affects filters and adjustments.