[Insight-users] downsampling a 3D volume

[michiel mentink]

>>I think that only changes the spacing of the image artificially and does
not change the image size and its contents.

I think changing the pixel spacing does change the image size. There is no
property attached to an image that gives it
"image size".
The image size is calculated by multiplying pixelspacing with the number of
pixels.

When you use a linear interpolator, you inherently apply a low-pass filter
to your pixels, which makes the picture more
blurry.

Feel free to correct me when I'm wrong.

cheers, Michael

On Tue, Mar 30, 2010 at 11:43 PM, Kishore Mosaliganti <kishoreraom at gmail.com
> wrote:

> I think that only changes the spacing of the image artificially and does
> not change the image size and its contents.
>
> It is best to use a ResampleImageFilter and you can set the output spacing
> and size of the output image:
>
>   ResampleFilterType::Pointer resample = ResampleFilterType::New();
>   resample->SetTransform ( transform ); // identity transform
>   resample->SetInterpolator ( interp ); // linear interpolator
>   resample->SetInput ( reader->GetOutput() );
>   resample->SetSize ( size );
>   resample->SetOutputOrigin ( origin );
>   resample->SetOutputSpacing ( spacing );
>   resample->SetDefaultPixelValue ( 0 );
>   resample->Update();
>
> Kishore
>
>
> On Tue, Mar 30, 2010 at 5:40 PM, michiel mentink <
> michael.mentink at st-hughs.ox.ac.uk> wrote:
>
>> I think the easiest option for you would be just to open an image, and
>> then
>> decrease the pixel size.
>> After opening an image, the pixel size is just a property of the matrix
>> with
>> pixel values.
>>
>> You can get that property with
>>
>>
>>  image=reader->GetOutput(); // open your image
>>
>> ImageType::SpacingType sp = image->GetSpacing();
>>    std::cout << "Spacing = ";
>>    std::cout << sp[0] << ", " << sp[1] << ", " << sp[2] << std::endl;
>>
>> Then, divide all spacing parameters by 1.07:
>>
>> sp[0] = sp[0]/1.07;
>> sp[1] = sp[1]/1.07; // etc.
>>
>> and then set the spacing:
>>
>> image->SetSpacing(sp)
>>
>> After that, you will have changed the dimension of your image without
>> having
>> touched any of your pixels. Ideal.
>>
>> cheers, Michael
>>
>>
>>
>> On 3/30/10, Reda, Fitsum A <fitecx at gmail.com> wrote:
>> > Hi all,
>> >
>> > I wanted to downsample CT volumes using floating point scale , say,
>> > (scale_x, scale_y,scale_z) = (1.07, 1.07, 1.07);
>> > I would really appreciate any help with this. I am kind of getting
>> started
>> > with itk.
>> >
>> > Thanks in advance,
>> > Reda
>> >
>> >
>> >
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