| | 1 | == July 25, 2012 == |
| | 2 | |
| | 3 | I looked into Fourier transforms of bias data, based on reports (see [http://asd.gsfc.nasa.gov/Bernard.Rauscher/Research/Publications_files/article.pdf]) that the read noise can be improved via a Fourier process. The method described assumes that the correlated noise arises due to a time dependent component that is difficult to detect. Therefore, in order to examine this, I asked Sidik for the read out times that could be used to flag each pixel with a given time. Sidik responded that the pixels are read out as |
| | 4 | |
| | 5 | {{{ |
| | 6 | T(x,y) = x * dt + y * (dt2 + e2 + delta2) |
| | 7 | }}} |
| | 8 | |
| | 9 | where x and y are the pixel coordinates on a cell, dt is the readout time for a pixel (dt = 2030ns), dt2 is the time to shift rows down (dt2 = 89880ns), e2 is a constant unknown error in dt2 (e2 <= 100ns), and delta2 is a jitter component (delta2 = +/- 10-20ns). As e2 and delta2 are small relative to dt2, they were ignored entirely. |
| | 10 | |
| | 11 | To prepare the pixel data to allow for an FFT, the image mean was subtracted (to zero the DC component), and the pixels were indexed based on dt, such that |
| | 12 | {{{ |
| | 13 | i(x,y) = x + int(y * 89880 / 2030) / y |
| | 14 | }}} |
| | 15 | with all unpopulated values of i zero-padded. |
| | 16 | |
