As the photometric preprocessing I means photometric corrections:
- correction for dark current (dark frame),
- removing of preamplifier offset (bias),
- correct a variable light response of (CCD) detector together with whole optical system (flat-field).
New approach is modeled as following the widely reccomended method in today. A photometrically corrected image Icij is computed for every input image Iij as
Icij = (Iij - t Dij - Bij) / fij,
where i,j is an index of a pixel, Dij is a dark frame t is ratio of exposure times of I and D. Bij is the bias and fij is normalized flat-field frame (to save absolute photometric fluxes):
fij = Fij / 〈Fij〉.
〈Fij〉 means averaged level determined by robust mean.
I think the change does not cause any controversy. More over:
- The older approach is still available when bias is treated as zero.
- From previous point of view, the approach is just primary a new façade for users. More easy user's usage.
- User is not confused. The method is exactly the same as textbooks describes.
- Important parts of algorithms are the same, changes in functional parts are minor.
- Observation time save. A long-exposure dark would be prepared and applied to all shortest exposures (also on longer ones, but the noise can devalue frames).
- Bias exposures are very short, so acquisition of a lot of biases it is not too time consuming.
- Processing tools has improvements in use of previous data products and no temporary reduction of frames are created.