| | 1 | == October 8, 2013 == |
| | 2 | |
| | 3 | Notes on fftP pattern correction/row-to-row bias offset issue. |
| | 4 | |
| | 5 | The mathematical process for fftP is as follows, for an input image I: |
| | 6 | |
| | 7 | * Remove median: |
| | 8 | * R = I - median(I) |
| | 9 | * Clip signals: |
| | 10 | * S = R * (R > 5 * sigma_MAD(R)) |
| | 11 | * R = R - S |
| | 12 | * Taper: |
| | 13 | * R = R * sinc((x - 0.5 xsize)/xsize) * sinc((y - 0.5 ysize)/ysize) |
| | 14 | * FFT: |
| | 15 | * C = FFT(R) |
| | 16 | * Censor: |
| | 17 | * C[abs(u) < Ulimit][abs(v) > Vlimit] = 0.0; |
| | 18 | * IFFT: |
| | 19 | * T = IFFT(C) |
| | 20 | * Untaper: |
| | 21 | * T = T / (sinc(x..) * sinc(y..)) |
| | 22 | * Restore signals: |
| | 23 | * T = T + S |
| | 24 | |
| | 25 | The images below show a set of IPP chip processed mosaics (top panels) and fftP processed raw mosaics (bottom panels) for the OTA/cell combinations listed in the tables. The fftP processed images have not been detrended in any way, and so retain burntool trails, corner glows, etc. The fftP processing has an odd set of NAN value masks that appear due to some error in my quick coding (these mirror the censored locations on the C image, so that's a likely culprit). I do not believe that these impact the rest of the pixels. The overscan region in the fftP frames is set to zero in the initial "R" image, but this is not repeated after the inverse FFT, so residual row-to-row "corrections" are visible in the region. All images have been scaled to the flux range of [-10:50], so the colorbars match. |
| | 26 | |
| | 27 | || o6567g0110o || OTA12 || OTA27 || OTA32 || |
| | 28 | || chip processed cell || xy45 || xy45 || xy45 || |
| | 29 | || chip PATTERN.ROW? || No || No || No (xy3v,xy7v only) || |
| | 30 | || fftP processed raw cell || xy45 || xy45 || xy45 || |
| | 31 | |
| | 32 | [[Image(r2r.jpg)]] |
| | 33 | |
| | 34 | || chip processed cell || xy13 || xy13 || xy13 || |
| | 35 | || chip PATTERN.ROW? || No || Yes || No || |
| | 36 | || fftP processed raw cell || xy45 || xy45 || xy45 || |
| | 37 | |
| | 38 | [[Image(r2r_butterfly.jpg)]] |
| | 39 | |
