Search found 88 matches

by imaggie
2012-01-07T09:56:58-07:00
Forum: Digital Image Processing
Topic: proper scaling of the Jinc filter for EWA use
Replies: 234
Views: 424240

Re: proper scaling of the Jinc filter for EWA use

This is not lens correction, it's motion blur and focussing error. ( If you're interested in that, look at GIMP's lens "distortion" , which can be used with negative values as a lens corrections. IIRC, it's a matrix op rather than convo ). very briefly, motion blur is a convolution with a line segme...
by imaggie
2012-01-07T06:36:54-07:00
Forum: Digital Image Processing
Topic: proper scaling of the Jinc filter for EWA use
Replies: 234
Views: 424240

Re: proper scaling of the Jinc filter for EWA use

lanczos3=" lz=zz/4.0; (abs(lz)<1) ? sinc(zz) / sinc(lz) : white" Just a quick aside. After much head banging I finally realised that to do the same thing in a deblur context, where the jinc or sinc is in the denominator , you need to divide by the window function not multiply. Seems embarrassingly ...
by imaggie
2012-01-04T20:35:04-07:00
Forum: Bugs
Topic: bad error trapping could cause unexpected shell commands
Replies: 8
Views: 14729

Re: bad error trapping could cause unexpected shell commands

$ convert -size $((5*$wid))x$((5*$ht)) xc: -tile (-extract 50%x25%+25%+5% tile.png)\ bash: syntax error near unexpected token `(' $ /tmpd/img $ -draw "rectangle 0,0 $((5*$wid)),$((5*$ht))" \ > output-tile.png There was no spaces on what I posted but you are in essence correct . The shell barfed bec...
by imaggie
2012-01-04T16:13:15-07:00
Forum: Bugs
Topic: FFT phase ?
Replies: 19
Views: 33936

Re: FFT phase ?

Yes magnitude and phase is a polar co-ord system, the complex plane in a cartesian representation. The two are equivalent expressions of the same thing, so a result in one frame cannot confirm a result in the other , it's the same thing. I still believe the fact that I can reproduce the mag/phase im...
by imaggie
2012-01-04T13:35:20-07:00
Forum: Bugs
Topic: FFT phase ?
Replies: 19
Views: 33936

Re: FFT phase ?

But I really don't know how to interpret the phase profile. It seems to have very high frequency oscillations within slower osciallations, the later of which seem to match the cycles in the mag profile. I suspect the hf is spurious, I think the correct phase is a linear ramp. I know that FFTW is a ...
by imaggie
2012-01-04T13:25:16-07:00
Forum: Bugs
Topic: FFT phase ?
Replies: 19
Views: 33936

Re: FFT phase ?

Oh please, don't quote WP as a reference for anything. It's like watching a Hollywood film "based on a true story" and imagining you are learning history. So are you saying that it is wrong. A lot of experts have contributed to Wikipedia. So there must be something to it. I cannot explain to you bu...
by imaggie
2012-01-04T03:39:53-07:00
Forum: Bugs
Topic: FFT phase ?
Replies: 19
Views: 33936

Re: FFT phase ?

http://www.fmwconcepts.com/misc_tests/FFT_v6744/square31_hdri_fft_mp-1.png now If I take a x=0 or y=0 section through that plot , it's about what I would expect: an even cyclic variation of phase. The light / dark discontinuity is in fact the -pi , +pi wrap around. I was expecting something more li...
by imaggie
2012-01-04T02:55:29-07:00
Forum: Bugs
Topic: FFT phase ?
Replies: 19
Views: 33936

Re: FFT phase ?

quote and link in first post. According to what I see and what you confirmed, it seems HDRI and non_HDRI are now scaled the same and it's not 0-2*pi. That is correct. They are both scaled to 0 to quantumrange so that the phase if easily visible without scaling. Internally they are used properly wit...
by imaggie
2012-01-04T02:47:27-07:00
Forum: Bugs
Topic: FFT phase ?
Replies: 19
Views: 33936

Re: FFT phase ?

The other issue I am still puzzled about is how these real and imaginary components relate to the fact that in the 1D (analog) fourier transform, the rect and sinc are transform pairs. No one ever states anything about the imaginary part. See table in http://en.wikipedia.org/wiki/Fourier_transforms...
by imaggie
2012-01-03T18:19:40-07:00
Forum: Bugs
Topic: FFT phase ?
Replies: 19
Views: 33936

Re: FFT phase ?

quote and link in first post. According to what I see and what you confirmed, it seems HDRI and non_HDRI are now scaled the same and it's not 0-2*pi.
by imaggie
2012-01-03T17:47:22-07:00
Forum: Bugs
Topic: FFT phase ?
Replies: 19
Views: 33936

Re: FFT phase ?

What part of the doc is broken -- where specifically? specifically the bit I noted above about non-HDRI being different. In fact non-HDRI seems to be as stated but the implication that HDRI is different has apparently not been the case " for a long time". When I went to the doc the try to understan...
by imaggie
2012-01-03T14:39:42-07:00
Forum: Bugs
Topic: crop and extact to png
Replies: 4
Views: 8357

Re: crop and extact to png

It does indeed. :oops:

IM has a learning curve like the foothills of the Himalayas , looks like I'm getting out of breath !

Many thanks.
by imaggie
2012-01-03T14:31:39-07:00
Forum: Bugs
Topic: FFT phase ?
Replies: 19
Views: 33936

Re: FFT phase ?

No roll is necessary for the image, unless you are using it as the filter function. Then it has to be rolled so as centered at 0,0. In my scripts such as fftconvol fftdeconvol, I do the roll of the spatial filter (only), not the image, internal to the script. So it is not necessary to do the roll e...
by imaggie
2012-01-03T13:20:19-07:00
Forum: Bugs
Topic: crop and extact to png
Replies: 4
Views: 8357

Re: crop and extact to png

many thanks for clearing that up.

How should I have know to do this? I have gone over the doc for -extract and crop many times now and see no indication that there is some residual information nor of the need to "repage".
by imaggie
2012-01-03T11:08:20-07:00
Forum: Bugs
Topic: crop and extact to png
Replies: 4
Views: 8357

crop and extact to png

Image

The above was created by the following command:

Code: Select all

convert -gravity NorthEast -crop "600x600+0+0" biche.jpg biche.png
It seems IM is producing something that has a different meaning to GIMP.

IM bug, GIMP bug or png spec abiguity?

thx