[Insight-users] PNGwriter writes wrong scaling information

[Bill Lorensen]

I think you should not convert the units. Just pass them in as they
are. For example, someone in astronomy may have different units that
someone in microscopy.


On Tue, Dec 11, 2012 at 9:42 AM, Dženan Zukić <dzenanz at gmail.com> wrote:
> 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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