Podobny efekt udało mi się ostatniu uzyskać używając nieprawidłowych biasów lub wcale ich nie używając - nie używając darków musisz używac prawidłowych bisaów
http://deepskystacker.free.fr/english/theory.htm
Flat-Field Frame CalibrationEach pixel in the CCD camera has a slightly different sensitivity to light. These sensitivity differences add another noise component to the image (known as flat-fielding error) unless steps are taken to compensate. While flat-fielding correction is important for achieving good quality images, it is absolutely essential for accurate photometric measurements.
With a bright background, any pixel-to-pixel variations in sensitivity are imprinted into the image; the more sensitive pixels show up as brighter dots. There are several common sources of flat-fielding variations. Typical CCD sensors have pixel-to-pixel variations on the order of 1%. Vignetting in the optical system can reduce the light flux at the corners of the sensor. Dust on optical surfaces near the sensor can cast shadows.
To create a flat-field frame, the optical system is illuminated by a uniform light source and an exposure is taken. To avoid non-linearity at the top and noise at the bottom, the exposure is usually chosen to get an average value of 30% to 50% of the saturation level. The flat-field is then renormalized by dividing each pixel into the average value in the array. Any pixel that is more sensitive will be assigned a number slightly below 1; any pixel that is less sensitive will be assigned a number slightly above 1. When this frame is multiplied by a raw image, it removes the sensitivity variations.
Flat-fielding must be done carefully. The entire aperture of the optical system must be evenly illuminated with light – if this is not done very carefully, then the flat-field will be wrong. Light leaks will ruin the calibration by adding unfocussed light that did not pass through the optical system. The flat-field pattern is different for each objective. Some sensors have significant flat-field variation as a function of wavelength (color). Changing the illumination levels usually affects the color temperature of the light source, requiring flat-fields and color balance adjustments to be repeated.
One simple approach for bright field microscopy is to remove the slide, and take images of the bright field. This is a good approach since the CCD sensor is illuminated in a fashion very similar to actual usage.
The flat-field frames themselves must be calibrated to remove bias, and for longer exposures dark correction must also be performed. It is essential that both the flat-field frames and light frames are properly bias corrected; otherwise the flat-field operation will not work correctly (mathematically, subtraction and division are not commutative). You can do this manually first, or just let MicroCCD do it automatically as part of the full calibration procedure.