[Insight-users] AddPixelAccessor set function confusion

[Luis Ibanez]

Hi Robert,

The test for the AddImageAdaptor
(and indirectly the AddPixelAccessor)
has bee posted to Gerrit at

http://review.source.kitware.com/#change,553


     Thanks


            Luis


-----------------------------------------------
On Sat, Dec 11, 2010 at 9:13 AM, Luis Ibanez <luis.ibanez at kitware.com> wrote:
> Hi Robert,
>
> Thanks for reviewing the other pixel accessors.
>
> In those, you have indeed found a collection of bugs.
>
> I have logged a bug entry here:
> http://public.kitware.com/Bug/view.php?id=11597
>
>
> In Summary:
>
> * AbsImageAdaptor (may not be fixable)
> * AcosImageAdaptor (fixable - within numerical range)
> * AsinImageAdaptor (fixable - within numerical range)
> * AtanImageAdaptor (fixable - within numerical range)
> * ComplexToImaginary (fixable)
> * ComplexToModulus (not fixable)
> * ComplexToPhase (not fixable)
> * ComplexToReal (fixable)
> * CosImageAdaptor (fixable - within numerical range)
> * ExpImageAdaptor (fixable - within numerical range)
> * ExpNegativeImageAdaptor (fixable - withing numerical range)
> * Log10ImageAdaptor (fixable - withig numerical range)
> * LogImageAdaptor (fixable - within numerical range)
> * RGBToLuminanceAdaptor (possible to trick..)
> * SinImageAdaptor (fixable - within numerical range)
> * SqrtImageAdaptor (fixable - within numerical range)
> * TanImageAdaptor (fixable - within numerical range)
>
>
> For example, the Trigonometric image Adaptors,
> have all the problem that you identified. (e.g.
> Sin is computing vcl_sin in both the Set and Get
> operators).
>
> These ones could be fixed by using the inverse
> trigonometric functions, but with the natural
> ambiguity of angles in the circle.
>
>   sin( 150 degrees ) --> sin( 30 degrees )
>
> So SinImageAdaptor should do
>
>   Get(x)  : vcl_sin(x)
>   Set(x)  : vcl_asin(x)
>
> Similar partial matches can be solved for
>
> Exp <----> Log
>
> While the case of RGBToLuminance can be
> tricked by storing an RGB value that results
> in the same luminance.
>
> The ComplexToYYY  are for the most part
> not fixable.
>
> More comments follow below...
>
> -------------------------------------------------------
> On Fri, Dec 10, 2010 at 2:19 PM, robert tamburo
> <robert.tamburo at gmail.com> wrote:
>> Thanks for the response Luis. I'm still confused though because none of the
>> other pixel accessors use the Set() method for inverse operations,
>> e.g., SqrtPixelAccessor, all of the trigonometric accessors, etc. I wrote
>> some code using SqrtPixelAdaptor (AddPixelAccessor will not compile, see
>> below) to test the Set() and Get() methods.
>> For an image set to 100:
>> - Get() returns 10 as expected.
>> - Set(10) sets the pixel to sqrt(10), and followed by Get() returns the
>> sqrt(sqrt(10)), which is what you warned me about. But is this the intended
>> use of Set()?
>> Back to your example with AddPixelAccessor:
>> It is my understanding that image adaptors behave like images. So SetPixel
>> would set the pixel value according to the pixel accessor used. So, by your
>> example, SetPixel(12) would ultimately just set the pixel to "7", which is
>> the value of the input image. It allows Get() to be used correctly, but
>> doesn't seem too useful.
>
> Why not ?
>
> What other use should we expect
> from the Get() / Set() methods ?
>
>> Considering that itkAddPixelAccessor will not compile and there is no test
>> for it,
>
>
> The lack of test is a bug.
>
> I'm fixing that one using the one by starting
> from the file that you kindly provided.
>
>
>> and that its Set() method does not follow the other Accessors, is it
>> possible that the functionality for Set() was changed some time ago
>> and itkAddPixelAccessor  fell through the cracks?
>
>
> That's a plausible theory,...
>
> but experimental inspection reveals that
> this is not the case:
>
> The following command will show you the
> history of these two classes.
>
>  gitk itkAddImageAdaptor.h
>  gitk itkAddPixelAccessor.h
>  gitk itkCosImageAdaptor.h
>
>  git log -- itkAddPixelAccessor.h
>  git log -- itkAddImageAdaptor.h
>  git log -- itkCosImageAdaptor.h
>
> ---
>
>   "Glimpsing at the source,
>    leaves no doubt"
>
>
>      Luis
>
>
> -----------------------------
>> Thanks.
>> ********
>> I attempted to write test code for AddPixelAccessor, but am getting compile
>> errors:
>> typedef itk::AddPixelAccessor<float> AddAccessorType;
>> itkAddPixelAccesor.h: No such file or directory
>> I made a copy of itkAddPixelAccesor.h (itkTestAddPixelAccessor.h), and
>> received the following error:
>> error: expected initializer before'<' token
>> which usually means the header wasn't included...
>> I moved #include "itkTestAddPixelAccessor.h" to the top of my include list
>> and got the following error:
>> itkTestAddPixelAccessor.h:39: error: invalid function declaration
>> Consider me perplexed...
>