[Insight-users] Re: Re: Histogram bug with maximum possible value ?

[Gaetan Lehmann]

Hi,

I have created a new bug report
http://www.itk.org/Bug/bug.php?op=show&bugid=3351&pos=4

Regards,

Gaetan


On Thu, 08 Jun 2006 08:33:29 +0200, Dr. Uwe Köhler <U.Koehler at gmx.de>  
wrote:

> Dear Karthik,
>
> I can confirm that there is a problem with the histogram class. From my
> earlier posting:
>
> I hope somebody can help me out with a (hopefully) easy, but important
> question. When using the ImageHistogram1 example to look at a grayscale  
> image
> with 15 gray values in the range from 0 to 255, I get all the gray values
> listed correctly appart from the ones valued 255. My guess is that this  
> has
> to do with the fact that the histogram size is given as 255 for 256  
> possible
> gray value, but I am not sure. I tried a size of 256, but it leads to an
> unsigned char overflow and the results are wrong.
>
> I had to write my own histogram class to avoid the problem for now.
>
> Cheers
>
> Uwe
>
>> Message: 5
>> Date: Wed, 07 Jun 2006 17:53:37 -0400
>> From: Karthik Krishnan <Karthik.Krishnan at kitware.com>
>> Subject: Re: [Insight-users] Histogram bug with maximum possible value
>> 	?
>> To: Gaetan Lehmann <gaetan.lehmann at jouy.inra.fr>
>> Cc: "insight-users at itk.org" <insight-users at itk.org>,
>> 	"Insight-developers \(E-mail\)" <insight-developers at itk.org>
>> Message-ID: <44874AE1.5090407 at kitware.com>
>> Content-Type: text/plain; charset=ISO-8859-15; format=flowed
>>
>> The histogram class is a widely used class. Please file a bug report and
>> assign it to me with a high priority.
>>
>> -----
>>
>> That said, I am surprised, it does not handle pixels with intensity 255.
>> See lines 90-102 of
>> http://www.itk.org/cgi-bin/viewcvs.cgi/Code/Numerics/Statistics/itkListSamp
>> leToHistogramGenerator.txx?annotate=1.14&root=Insight
>>
>>         h_upper[i] = ((THistogramMeasurement) upper[i]) +
>>           NumericTraits< THistogramMeasurement >::One ;
>>         if(h_upper[i] <= upper[i])
>>           {
>>           // an overflow has occurred therefore set upper to upper
>>           h_upper[i] = upper[i];
>>           // Histogram measurement type would force the clipping the max
>> value.
>>           // Therefore we must call the following to include the max  
>> value:
>>           m_Histogram->SetClipBinsAtEnds(false);
>>           }
>>
>> If pixel type is UCHAR, it should go into that if block and do the
>> SetClipBinsAtEnds(false) thing. That would mean that the bins at the
>> edges of the histogram extend to infinity, so really 255 should be
>> considered.   [ In the default case, the ends are clipped, See
>> constructor of itk::Histogram with sets ClipBinsAtEnds to true (so 255
>> won't be considered), but that's not the case with you since you are
>> using the ScalarImageToHistogramGenerator.  ]
>>
>>
>> Thanks for reporting this.
>> -karthik
>>
>> Gaetan Lehmann wrote:
>> > Hi,
>> >
>> > I am the only one to have this problem ?
>> > Should I file a bug report ?
>> >
>> > Gaetan
>> >
>> >
>> > On Fri, 02 Jun 2006 17:11:45 +0200, Gaetan Lehmann
>> >
>> > <gaetan.lehmann at jouy.inra.fr> wrote:
>> >> I forgot to say I'm using ITK 2.6.0 with gcc 4.0
>> >>
>> >> On Fri, 02 Jun 2006 16:23:25 +0200, Gaetan Lehmann
>> >>
>> >> <gaetan.lehmann at jouy.inra.fr> wrote:
>> >>> Hi,
>> >>>
>> >>> I'm trying to manipulate histograms, with itk::Histogram. I'm
>> >>> generating
>> >>> the histogram from an image with the ScalarImageToHistogramGenerator
>> >>> class. The pixel type of the input image is unsigned char.
>> >>> Everything seems to work, as long as there is no pixel value = 255
>> >>> in  the
>> >>> image.
>> >>> All the pixels with an intensity of 255 are not counted in the
>> >>> histogram.
>> >>> For example, the attached image (a 10x10 black image with 4 white  
>> (255)
>> >>> pixels) produce an histogram with 96 pixels according to the
>> >>> GetTotalFrequency() result.
>> >>>
>> >>> Is it a bug ?
>> >>> Or I have missed something ?
>> >>>
>> >>> Regards,
>> >>>
>> >>> Gaetan
>>
>
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-- 
Gaëtan Lehmann
Biologie du Développement et de la Reproduction
INRA de Jouy-en-Josas (France)
tel: +33 1 34 65 29 66    fax: 01 34 65 29 09
http://voxel.jouy.inra.fr