Sharpening "A sharp" - what do the numbers mean?

Started by DRWin, June 13, 2021, 03:05:45 PM

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DRWin

June 13, 2021, 03:05:45 PM
Sharpening is often a finely-calibrated process involving some trial and error to get the right amount. 
The "A-sharp" filter on Avidemux is great, but a bit hard to use since to really see the results one must apply the filter and then save the clip so that it can be viewed at a larger size to see details, so as to determine if there is too much or too little sharpening.  This is very time-consuming. 
Absent any way of viewing the clip at larger sizes (default view is the upper left corner of the frame, which when shooting outdoors is usually blank blue sky) it would be beneficial to know what exactly the settings "Threshold" and "Strength" mean as used in the "A-sharp" filter.  Can anyone tell me?
Thanks!

DRWin

#1
June 13, 2021, 03:13:58 PM
Quote from: DRWin on June 13, 2021, 03:05:45 PMSharpening is often a finely-calibrated process involving some trial and error to get the right amount. 
The "A-sharp" filter on Avidemux is great, but a bit hard to use since to really see the results one must apply the filter and then save the clip so that it can be viewed at a larger size to see details, so as to determine if there is too much or too little sharpening.  This is very time-consuming. 
Absent any way of viewing the clip at larger sizes (default view is the upper left corner of the frame, which when shooting outdoors is usually blank blue sky) it would be beneficial to know what exactly the settings "Threshold" and "Strength" mean as used in the "A-sharp" filter.  Can anyone tell me?
Thanks!
Forgot to include: what does "Block adaptive" mean, and what does it do? 

eumagga0x2a

#3
June 13, 2021, 10:27:22 PM
Quote from: DRWin on June 13, 2021, 03:05:45 PMThe "A-sharp" filter on Avidemux is great, but a bit hard to use since to really see the results one must apply the filter and then save the clip so that it can be viewed at a larger size to see details

You can use the trick with the crop filter temporarily added after the Asharp filter. The preview in the filter manager after the crop filter allows you to magnify the remaining part of the picture. This is not exactly comfortable, but presumably much faster than saving the video.

DRWin

#5
June 14, 2021, 02:33:42 PM
Quote from: butterw on June 13, 2021, 05:08:52 PMhttp://avisynth.nl/index.php/ASharp
Thanks for the link.  Questions remain.
1. float  T = 2.0
Unsharp masking threshold.
0 will do nothing, 1 will enhance contrast 1x.
Range is from 0 to 32.
"Enhance contrast 1x" (or 2x or whatever) is very fuzzy - how is "contrast" defined in terms of visibility or clarity?
2. float  D = 4.0
Adaptive sharpening strength to avoid sharpening noise.
If greater than 0, the threshold is adapted for each pixel (bigger for edges) and t acts like a maximum.
"t acts like a maximum": what is "t"?  Is it "T" (upper case) as "float T=2.0"?  If so, why is default "D" set at 4.0 when T is set at 2.0?
So my question remains unanswered in practical terms.

It would be far more helpful to describe these functions and numbers in terms like those commonly used in photo image sharpening: size of effect (expressed as number of pixels) and percentage/intensity of effect.



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