[Insight-users] How to cast from RGB to short?

[Michael Xanadu]

Hi Gaëtan,

thank you for your support. Actually, I thought that there's a difference in
the number of segments between using <long> or colormapper for the output of
watershed filter. It seemed to me that I receive more segments by using a
RGB output. I found out that the problem lies in the viewer I use to watch
the images. It had a wrong color level and showed the image to bright, so
that a lot of segments disapeared.
The clue of watershed is, that it delivers no single segment I'm looking
for, but all segments it can find. To extract a single segment, I want to
use Connected Threshold (with seed) afterwards. That was the reason I asked
for help.

Regards, Michael



2009/8/31 Gaëtan Lehmann <gaetan.lehmann at jouy.inra.fr>

>
> Le 31 août 09 à 15:33, Michael Xanadu a écrit :
>
>
>  Hi,
>>
>> I've got a watershed filtered image processed by a colormapper. So it's an
>> image of type:
>>
>>    typedef itk::RGBPixel<short>   RGBPixelType;
>>    typedef itk::Image<RGBPixelType, 2>    RGBImageType;
>>
>> Now I want to filter that image with a connected threshold filter, because
>> I need it this way.
>> But ConnectedThresholdImageFilter can't process such RGB images.
>> I tryed to convert the image into a short type by using CastImageFilter,
>> too.
>> But I always get:
>>
>>    error C2440: 'static_cast' : cannot convert from
>> 'itk::RGBPixel<TComponent>' to 'short'
>>
>> So how can I cast from RGB to short? Or how to filter a RGB image with a
>> connected threshold filter?
>>
>>
> You can extract one of the channels with
> VectorIndexSelectionCastImageFilter or go to an intensity image with
> RGBToLuminanceImageFilter, but I doubt that's what you want. The color image
> is only a representation of the watershed output easier to read for humans,
> but not for computer. If you want to work on the output of the watershed,
> it's better to not use a color mapper, but directly on the output image of
> the watershed - the image should be of type itk::Image< unsigned long, 2 >.
>
> And even if you don't use a color mapper, it may not be a good idea to
> process the output of the watershed filter (a labeled image) with a filter
> (ConnectedThresholdImageFilter) made to work on a grayscale images.
>
> Can you explain what you want to achieve?
>
> Regards,
>
> Gaëtan
>
> --
> 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  http://www.itk.org
> http://www.mandriva.org  http://www.bepo.fr
>
>
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