Vignetting coefficients
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Stephan Weber
Jun 28, 2026, 10:01:33 AMJun 28
to PTGui Support
Hi,
x y(wanted)
0.0 1
0.1 0.95
0.2 0.85
0.3 0.8
0.4 0.75
0.5 0.75
0.6 0.75
0.7 0.75
0.8 0.72
0.9 0.65
1.0 0.58
I want to follow or create a certain vignetting compensation:
x y(wanted)
0.0 1
0.1 0.95
0.2 0.85
0.3 0.8
0.4 0.75
0.5 0.75
0.6 0.75
0.7 0.75
0.8 0.72
0.9 0.65
1.0 0.58
So it has a peak left (=middle), then flat, then the usual outer compensation.
If I know the formula, it should be easy with Excel.
But it looks the coeffs are not a simple polynominal. Can you tell me the formula? I am using v12.27.
Bye Stephan
Erik Krause
Jun 28, 2026, 10:23:30 AMJun 28
to pt...@googlegroups.com
Am 28.06.2026 um 16:01 schrieb Stephan Weber:
> But it looks the coeffs are not a simple polynominal.
See here:
> But it looks the coeffs are not a simple polynominal.
https://groups.google.com/g/ptgui/c/0PU_2CX4Ofs/m/-5tniAVPDwAJ
--
Erik Krause
http://www.erik-krause.de
PTGui Support
Jun 28, 2026, 2:20:35 PMJun 28
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Hi Stephan,
If I remember correctly, the first (x^0) coefficient is always 1. So the
curve always starts at 1.0.
The radius is normalized from 0 in the center to 1 at the corners. For
circular fisheye images this means that only the part between 0 and
sqrt(2)/2 is actually used, and PTGui will show only that part of the
curve in the Exposure/HDR tab.
Kind regards,
Joost Nieuwenhuijse
www.ptgui.com
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If I remember correctly, the first (x^0) coefficient is always 1. So the
curve always starts at 1.0.
The radius is normalized from 0 in the center to 1 at the corners. For
circular fisheye images this means that only the part between 0 and
sqrt(2)/2 is actually used, and PTGui will show only that part of the
curve in the Exposure/HDR tab.
Kind regards,
Joost Nieuwenhuijse
www.ptgui.com
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Stephan Weber
Jun 28, 2026, 3:04:43 PMJun 28
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Hi Joost
I wonder what is the full formula?
I manage to adjust by hand some simple cases which I use when the optimizer does not work.
But how can I get these more difficult table?
I need a rounding for app 20% , then flat then a quite standard roll off.
With a 10th polynomial it should be possible to get an overall error well below 0.01 rms.
Bye Stephan
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Stephan Weber
Jul 1, 2026, 12:26:04 PMJul 1
to pt...@googlegroups.com
Hi I assumed the formula is like y=1+a1x^2+a2*x^3 etc but then plotting this in xls and with ptgui I got no real much in complex cases. So I believe it is a bit more than this.
Bye Stephan
PTGui Support
Jul 1, 2026, 2:24:19 PMJul 1
to pt...@googlegroups.com
Hi Stephan,
The x^1 is missing, it should be something like this:
y=1+a1x^1+a2*x^2
> <mailto:ptgui%2Bunsu...@googlegroups.com>
> > <mailto:ptgui+un...@googlegroups.com
> <mailto:ptgui%2Bunsu...@googlegroups.com>>.
> > ptgui/94d2e85b-6acc-4ac5-a117-
> ce9762fd400dn%40googlegroups.com <http://40googlegroups.com>
> <https://
> > groups.google.com/d/msgid/ptgui/94d2e85b-6acc-4ac5-a117-
> <http://groups.google.com/d/msgid/ptgui/94d2e85b-6acc-4ac5-a117->
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> utm_medium=email&utm_source=footer <http://40googlegroups.com?
> groups.google.com/d/msgid/ptgui/40f11a42-dc70-4ec4-
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The x^1 is missing, it should be something like this:
y=1+a1x^1+a2*x^2
On 7/1/26 18:25, Stephan Weber wrote:
> Hi I assumed the formula is like y=1+a1x^2+a2*x^3 etc but then plotting
> this in xls and with ptgui I got no real much in complex cases. So I
> believe it is a bit more than this.
>
> Bye Stephan
>
> Stephan Weber <weberc...@gmail.com <mailto:weberc...@gmail.com>>
> Hi I assumed the formula is like y=1+a1x^2+a2*x^3 etc but then plotting
> this in xls and with ptgui I got no real much in complex cases. So I
> believe it is a bit more than this.
>
> Bye Stephan
>
> schrieb am So., 28. Juni 2026, 21:04:
>
> Hi Joost
>
> I wonder what is the full formula?
> I manage to adjust by hand some simple cases which I use when the
> optimizer does not work.
> But how can I get these more difficult table?
> I need a rounding for app 20% , then flat then a quite standard
> roll off.
> With a 10th polynomial it should be possible to get an overall error
> well below 0.01 rms.
> Bye Stephan
>
> 'PTGui Support' via PTGui Support <pt...@googlegroups.com
>
> Hi Joost
>
> I wonder what is the full formula?
> I manage to adjust by hand some simple cases which I use when the
> optimizer does not work.
> But how can I get these more difficult table?
> I need a rounding for app 20% , then flat then a quite standard
> roll off.
> With a 10th polynomial it should be possible to get an overall error
> well below 0.01 rms.
> Bye Stephan
>
> 'PTGui Support' via PTGui Support <pt...@googlegroups.com
> <mailto:pt...@googlegroups.com>> schrieb am So., 28. Juni 2026, 20:20:
>
> Hi Stephan,
>
> If I remember correctly, the first (x^0) coefficient is always
> 1. So the
> curve always starts at 1.0.
>
> The radius is normalized from 0 in the center to 1 at the
> corners. For
> circular fisheye images this means that only the part between 0 and
> sqrt(2)/2 is actually used, and PTGui will show only that part
> of the
> curve in the Exposure/HDR tab.
>
> Kind regards,
>
> Joost Nieuwenhuijse
> www.ptgui.com <http://www.ptgui.com>
>
> Hi Stephan,
>
> If I remember correctly, the first (x^0) coefficient is always
> 1. So the
> curve always starts at 1.0.
>
> The radius is normalized from 0 in the center to 1 at the
> corners. For
> circular fisheye images this means that only the part between 0 and
> sqrt(2)/2 is actually used, and PTGui will show only that part
> of the
> curve in the Exposure/HDR tab.
>
> Kind regards,
>
> Joost Nieuwenhuijse
> > <mailto:ptgui+un...@googlegroups.com
> <mailto:ptgui%2Bunsu...@googlegroups.com>>.
> > To view this discussion visit https://groups.google.com/d/
> msgid/ <https://groups.google.com/d/msgid/>
> > ptgui/94d2e85b-6acc-4ac5-a117-
> ce9762fd400dn%40googlegroups.com <http://40googlegroups.com>
> <https://
> > groups.google.com/d/msgid/ptgui/94d2e85b-6acc-4ac5-a117-
> <http://groups.google.com/d/msgid/ptgui/94d2e85b-6acc-4ac5-a117->
> > ce9762fd400dn%40googlegroups.com?
> utm_medium=email&utm_source=footer <http://40googlegroups.com?
> utm_medium=email&utm_source=footer>>.
>
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Stephan Weber
Jul 1, 2026, 3:13:40 PMJul 1
to PTGui Support
Hi, I attached 3 pictures (srinked to 50%) which have initially little vignetting. Then I added a strong artificial vignette with strong bright peak in the middle and usual dark roll-off in the edges. So the fitting result by PTGUI should hit that artificial S-curve by doing an optimization. 
Basically it works , but not well, the center behavior is far too soft! And the outer roll-off too weak (see the attached dark picture). So the optimizer makes no real good job (last screenshot).
Can PTGUI team check this, and may improve the optimizer?
Note: Such strange vignetting is very real for many lenses used for IR photography.
See last photo:
Bye Stephan
PTGui Support
Jul 1, 2026, 4:45:44 PMJul 1
to pt...@googlegroups.com
Hi Stephan,
I'm sorry, I don't think it's a good idea to try to optimize PTGui for
artificially deteriorated images. It also looks unnatural, very
different from the natural vignetting in your _50p image.
If you have real life images where PTGui does a bad job I'd be happy to
investigate.
On 7/1/26 21:13, Stephan Weber wrote:
> DSC00317V.JPGDSC00318V.JPGDSC00319V.JPG
> > www.ptgui.com <http://www.ptgui.com> <http://www.ptgui.com
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> groups.google.com/d/msgid/ptgui/3d764633-43d7-4eb7-
> ae01-12436884b6aen%40googlegroups.com?utm_medium=email&utm_source=footer>.
I'm sorry, I don't think it's a good idea to try to optimize PTGui for
artificially deteriorated images. It also looks unnatural, very
different from the natural vignetting in your _50p image.
If you have real life images where PTGui does a bad job I'd be happy to
investigate.
On 7/1/26 21:13, Stephan Weber wrote:
> DSC00317V.JPGDSC00318V.JPGDSC00319V.JPG
>
> Hi, I attached 3 pictures (srinked to 50%) which have initially little
> vignetting. Then I added a strong artificial vignette with strong bright
> peak in the middle and usual dark roll-off in the edges. So the fitting
> result by PTGUI should hit that artificial S-curve by doing an
> optimization. Gray127_Vigm25_centerPeak24M_boosted_50p.JPGptguivig.PNG
> Hi, I attached 3 pictures (srinked to 50%) which have initially little
> vignetting. Then I added a strong artificial vignette with strong bright
> peak in the middle and usual dark roll-off in the edges. So the fitting
> result by PTGUI should hit that artificial S-curve by doing an
> Basically it works , but not well, the center behavior is far too
> soft! And the outer roll-off too aweak (see the attached dark picture).
> So the optimizer makes no real good job (last screenshot).
>
> Can PTGUI team check this, and may improve the optimizer?
>
> Note: Such strange vignetting is very real for many lenses used for IR
> photography.
>
> See last photo:
>
> Can PTGUI team check this, and may improve the optimizer?
>
> Note: Such strange vignetting is very real for many lenses used for IR
> photography.
>
> See last photo:
> DSC00934_50p.JPG
>
> Bye Stephan
>
> PTGui Support schrieb am Mittwoch, 1. Juli 2026 um 20:24:19 UTC+2:
>
> Hi Stephan,
>
> The x^1 is missing, it should be something like this:
> y=1+a1x^1+a2*x^2
>
> Kind regards,
>
> Joost Nieuwenhuijse
> www.ptgui.com <http://www.ptgui.com>
>
> Bye Stephan
>
> PTGui Support schrieb am Mittwoch, 1. Juli 2026 um 20:24:19 UTC+2:
>
> Hi Stephan,
>
> The x^1 is missing, it should be something like this:
> y=1+a1x^1+a2*x^2
>
> Kind regards,
>
> Joost Nieuwenhuijse
> groups.google.com/d/msgid/>>
> > > ptgui/94d2e85b-6acc-4ac5-a117-
> > ce9762fd400dn%40googlegroups.com <http://40googlegroups.com>
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