[Insight-users] PNGwriter writes wrong scaling information

[Dženan Zukić]

PNG has three following units: meters, radians, and unknown. Currently PNG
reader ignores unit, and writes unknown units.

I guess I Should keep writing unknown units. But when reading PNG with
meter units (eg. 2000 pixels/meter), should I transform it into pixel
spacing 0.5 (assuming customary millimeter) or into 0.0005?


On Tue, Dec 11, 2012 at 3:36 PM, Bill Lorensen <bill.lorensen at gmail.com>wrote:

> No units. ITK considers units an application thing. You can add a unit
> type if the format supports it. It could help applications. For
> example, most medical images use mm's.
>
> On Tue, Dec 11, 2012 at 8:25 AM, Dženan Zukić <dzenanz at gmail.com> wrote:
> > Is ITK still assuming no units, or millimeters are units for pixel
> spacing?
> >
> >
> > On Mon, Dec 10, 2012 at 5:25 PM, Bill Lorensen <bill.lorensen at gmail.com>
> > wrote:
> >>
> >> If you submit a gerrit patch, I'll write or modify a test.
> >>
> >> How will we know if the fix works unless we test it? How will we know
> >> if someone reintroduces the bug if we don't test it?
> >>
> >>
> >> On Mon, Dec 10, 2012 at 10:41 AM, Dženan Zukić <dzenanz at gmail.com>
> wrote:
> >> > But this would be a bug fix, not a patch introducing new features.
> This
> >> > should already be working, and ideally having a test.
> >> >
> >> > I know that many bugs don't get fixed, because they are not important
> >> > enough
> >> > and there is not enough people working on ITK. However a requirement
> to
> >> > write a 20-30 line test for a few lines of fixed code is a great
> >> > deterrence
> >> > for me to contribute bug fixes (such as this one).
> >> >
> >> >
> >> > On Mon, Dec 10, 2012 at 4:26 PM, Bill Lorensen <
> bill.lorensen at gmail.com>
> >> > wrote:
> >> >>
> >> >> Looks like ti should be fixed. But if you submit a gerrit patch, make
> >> >> sure oyu also supply a test or modify an existing test.
> >> >>
> >> >> The lack of a test is why your previous gerrit patch has not been
> >> >> approved.
> >> >>
> >> >> Bill
> >> >>
> >> >> On Mon, Dec 10, 2012 at 8:35 AM, Dženan Zukić <dzenanz at gmail.com>
> >> >> wrote:
> >> >> > Hi everyone,
> >> >> >
> >> >> > I have noticed that ImageFileWriter, when writing png format,
> writes
> >> >> > wrong
> >> >> > pixel size information. It is not completely wrong, but it is not
> in
> >> >> > accordance with png specification.
> >> >> >
> >> >> > When reading such files with OpenCV, I get following warning:
> >> >> > libpng warning: Invalid sCAL ignored: invalid unit
> >> >> > This is not just annoying and clutter-causing, but displaying it
> for
> >> >> > every
> >> >> > single image slows down my OpenCV processing.
> >> >> >
> >> >> > I used XnView to batch-edit the extracted slices and set some
> scaling
> >> >> > which
> >> >> > adheres to the specification to get rid of this warning.
> >> >> >
> >> >> > Now the question: should I correct this bug, or submit a bug
> report?
> >> >> > My
> >> >> > last
> >> >> > bug-fixing ended non-gloriously :(
> >> >> >
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> >> >>
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> >> >
> >> >
> >>
> >>
> >>
> >> --
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> >
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