[magick-users] bug in depolar options?

[Anthony Thyssen]

On Fri, 1 May 2009 11:36:07 +0200
Jan Martin <janmartin3 at googlemail.com> wrote:

| Hello Anthony,
| 
| this is what I call really excellent support!
| 
| I looked at
| http://www.imagemagick.org/script/changelog.php
| and couldn't find anything regarding your changes.
| 
| Where to find the most up-to-date changelog and source?
| Where to download?
| 

It is the SVN repository. However be warned that sometimes
people upload something that is not quite complete, and upload
a fix or other changes a few minutes later.

See  http://www.imagemagick.org/script/subversion.php



| Where to download for 32 bit Ubuntu 9.04 Linux?
| I case I need to install from source, what files to download exactly?
| 
| Then to follow "Install from Unix source"?
| http://www.imagemagick.org/script/install-source.php
| 
As you are using ubuntu you may need to install from either SVN download
or a tar file.

I know how to generate Source RPM's from the source directory and
from that the normal RPM's 
  http://www.imagemagick.org/Usage/api/#building

But I have no instructions or idea how to generate DEB packages such
as used by Ubuntu.  It would be nice to know, and record, but I don't
know.

There is still a bug in the handling of the 'angles' for depolar,
which my last example...
| >  convert testimage2_diagram.jpg  -virtual-pixel black \
| >          -write show: \
| >          +distort depolar '212,35 212.5,212.5 135,225' \
| >          -write show: \
| >          +distort  polar  '212,35 212.5,212.5 135,225' \
| >          show:
| >

Can demonstrate (when you get the updates): the lake is extracted and
when 'polar' distorted it goes to the top as specified.  That is the
depolar gets the angles wrong, though it does get it right for -180,180
(the default).

I will work on that another time.


| Regarding your questions:
| 
| Not sure if you added a picture after
| > "convert testimage2_diagram.jpg +distort depolar '212.5,35' -rotate 180
| show:"
| At least I did not receive one using gmail online interface.
| 
No I did not send one.  The mailing list will not carry images in any
case.

If I can find a smaller image with better indications for angles (more
differences around the ring), then I will add examples to IM Examples for
using Rmin and angles.


| > QUESTION:   Are prople happy with 0 angle being straight down,
| > and the default 'cut point' for the ring being straight up?
| > Or would they prefer a different set of angles?
| 
| Don't know, I am just doing this for 3 days altogether.
| My best guess is to look how its done in other commands, and stay with that
| way to have it all work the same way. Maybe there are standards to follow?
| 
I think the angles were chosen to fit 'polar' distort better,

For example

   convert -pointsize 20 label:Anthony -virtual-pixel gray \
           +distort polar '100,80 0,0 -45,45' \
           -trim  +repage show:

will produce a 'smile like arc' on a grey background.


| Other thing is to make sure nothing breaks in  MagickWand, MagickCore,
| PerlMagick, Magick++ or peoples scripts etc.
| 
| My best gues is to just leave it as it is now.
| 
It shouldn't those just pass arguments to the DistortImages() function,
exactly as the command line API does.  I doubt it will break until
I start adding trianglular and grid mesh distortions.


| > WARNING:  this test image is NOT perfectly centered!
| >
| > It is also NOT a polar distortion, but a spherical image.
| >
| > The depolar image would need some serious cylindrical de-distorting to
| > remove the vertical compression at the top and bottom of the image, so as
| > to have it look reasonally 'normal'
| 
| 
| I am new to this. Please point me into the right direction.
| 
That image was taking with a 320 degree fish eye lens to get an image in just
about every direction all at once.  It is spherical.   Polar distorted image
is really a cone shaped image, not spherical.

It is hard to describe actually.


| Given that I know roughly where the doughnut hole is, is there a way to get
| the EXACT center of the doughnut automatically by analysing the black
| doughnut hole?
| Or whatever method?
| 
No idea actually.

| How would you approach the "serious cylindrical de-distorting"?
| Use another command instead of depolar? If  so, which?
| Or how to "de-distorting"?
| 
There is a major discussion of cylindrical distortions (wrapping a image
onto a cylinder such as a can).  In the IM discussion forum.




  Anthony Thyssen ( System Programmer )    <A.Thyssen at griffith.edu.au>
 -----------------------------------------------------------------------------
   Science, technology, and biology all use the woven rope of reality.
   Magic, on the other hand, functions by reweaving the fabric of reality.
                               -- Margret Weis & Tracy Hickman - "Dragon Wing"
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     Anthony's Home is his Castle     http://www.cit.gu.edu.au/~anthony/