[ITK-users] RandomImageSource is terrible no good not very random?

[Matt McCormick]

Hi Kent,

For A), the seed needs to be changed to get a different output.

HTH,
Matt

On Thu, Oct 27, 2016 at 12:57 PM, Kent Williams
<nkwmailinglists at gmail.com> wrote:
> I realize that itk::RandomImageSource is not meant to be a perfect source of
> randomness.  But it is pretty bad.  I was trying to generate a noise video
> with ITK -- by writing out 2D Images and then combining them using FFMPEG --
> and A) for a given set of dimensions, itk::RandomImageSource generates
> exactly the same image. and B) the resulting image is clearly not that
> random.
>
> I got better results (without much speed penalty) calling drand48 once per
> pixel.
>
> Link to image generated: https://flic.kr/p/Nz1p7w
>
> #include <iostream>
> #include <stdio.h>
> #include <sys/types.h>
> #include <unistd.h>
> #include <itkImage.h>
> #include <itkImageFileWriter.h>
> #include <itkImageRegionIterator.h>
> #include <itkRandomImageSource.h>
> #include <time.h>
> #include <stdlib.h>
> typedef itk::Image<unsigned char,2> ImageType;
> typedef itk::ImageFileWriter<ImageType> ImageFileWriter;
> typedef itk::RandomImageSource<ImageType> RandomImageSource;
> typedef itk::ImageRegionIterator<ImageType> Iterator;
>
> // 1080p
> //const int XSize(1920);
> //const int YSize(1080);
> const int XSize(1280);
> const int YSize(720);
>
> int main(int argc, char **argv) {
>
>
> ImageType::SizeType imageSize;
> imageSize[0] = XSize;
> imageSize[1] = YSize;
> // only used for the first GetBufferPointer method
> ImageType::Pointer image = ImageType::New();
> image->SetRegions(imageSize);
> image->Allocate();
>
> ImageFileWriter::Pointer writer = ImageFileWriter::New();
> for(unsigned i = 0; i < (60*24); ++i) {
> char fname[256];
> sprintf(fname,"%04u.tiff", i);
> writer->SetFileName(fname);
> #if 0
> // fill buffer with lrand48 results
> unsigned char *cp = image->GetBufferPointer();
> unsigned char *end = cp + (XSize * YSize);
> for(; cp < end; ++cp)
> *cp = lrand48();
> writer->SetInput(image);
> #else
> srand48(getpid() + time(NULL));
> RandomImageSource::Pointer rndSource = RandomImageSource::New();
> rndSource->SetSize(imageSize);
> writer->SetInput(rndSource->GetOutput());
> #endif
> writer->Update();
> std::cout << i << std::endl;
> }
> }
>
>
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