On Wed, Oct 09, 2013 at 08:16:41PM -0400, Matthew Hunt wrote: > To show the effects of pixel fill factor on aliasing, I coded up a > small simulation. This 1000x1000 starting image:
Awesome! > > https://dl.dropboxusercontent.com/u/20239870/Aliasing/micro-auto-focus-test-2.png > (from http://www.komar.org/faq/camera/auto-focus-test/ ) > > represents the image falling onto a 111x111 monochromatic pixel > sensor. Since each sensor pixel sees 9x9 pixels of the original image, > we can create 9x9 downsampling kernels to simulate various sensor > pixel fill factors. > > Here is the resulting image from a kernel using only a 1x1 portion of > the 9x9 kernel (1% fill factor, approximating "instantaneous" or > infinitesimal point sampling): > https://dl.dropboxusercontent.com/u/20239870/Aliasing/kernel_1.png > > A 3x3 kernel (11% fill factor): > https://dl.dropboxusercontent.com/u/20239870/Aliasing/kernel_3.png > > A 5x5 kernel (31% fill factor): > https://dl.dropboxusercontent.com/u/20239870/Aliasing/kernel_5.png > > A 7x7 kernel (61% fill factor): > https://dl.dropboxusercontent.com/u/20239870/Aliasing/kernel_7.png > > A 9x9 kernel (100% fill factor--no insensitive gap between pixels): > https://dl.dropboxusercontent.com/u/20239870/Aliasing/kernel_9.png > > And finally the code: > https://dl.dropboxusercontent.com/u/20239870/Aliasing/FillFactor.py > > You can see that the sensor pixel fill factor has a considerable > effect on the amount of aliasing in the output image. Very interesting. It would be a lot easier to see if you could have each point of your output be 9x9 pixels, then the resulting image would be the same size as the original (which is giving me aliasing on my display BTW). I suspect that if you sampled 18x18 pixels surrounding each pixel to create a new "original" that had been sent through a low pass filter, you would end up with no aliasing on any of the points. Many thanks for doing this, I think I just had a small nerdgasm. If I were to have time to hack it (unlikely, but...) would I just type /usr/bin/python FillFactor.py on the commmand line? > > On Wed, Oct 9, 2013 at 12:08 PM, Larry Colen <l...@red4est.com> wrote: > > It seems to me that if you had a rear illuminated sensor, with no space > > between the pixels, and it had no bayer filter, then aliasing/moire would > > not happen, because the light value would be averaged over the whole sample. > > > > It's the discontinuous aspect of what is effectively three overlayed photos > > that is causing the aliasing. > > > > Is this correct? > > > > -- > > Larry Colen l...@red4est.com http://red4est.com/lrc > > > > > > -- > > PDML Pentax-Discuss Mail List > > PDML@pdml.net > > http://pdml.net/mailman/listinfo/pdml_pdml.net > > to UNSUBSCRIBE from the PDML, please visit the link directly above and > > follow the directions. > > -- > PDML Pentax-Discuss Mail List > PDML@pdml.net > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and follow > the directions. -- Larry Colen l...@red4est.com http://red4est.com/lrc -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
