Colour processing of MYC CCD images

The images of NGC891 and M65/66 are assembled from MYC- and black/white images in the following way: On day 1 exposures are made without colour filters. After adding the images and processing with an unsharp masking technique the image L_grey results. On day 2 exposures are made using three colour filters M (Magenta), Y (Yellow) and C (Cyan), combined with an IR-blocking filter. The exposures are added and the resulting M-, Y- and C-images are converted to RGB images using the next formula (pixel by pixel):

R=Y+M-C
G=Y+C-M
B=C+M-Y

A possible background in these images is subtracted and the images are balanced by multiplying the images by certain constants. These constants are determined using exposures of the moon for which the R, G and B-components should be nearly equal. For the MYC filter set I use, and the FTT1010-M CCD chip the following multiplication constants are used:

R: 1.07
G: 1.00 (by definition)
B: 2.26

Next, the for the eye apparent intensity is calculated according to:

L_eye=0.299*R+0.587*G+0.114*B

The L_eye image now gives the intensity component of the colour image and is replaced by L_grey of day 1, by simply (pixel-wise) multiplying the R, G and B values by the ratio L_grey/L_eye. This results in a sharper and of higher quality image with intensity L_grey without affecting its colour.
Optionaly the L_eye image can be taken and processed (filtered and sharpened) giving an optimized L_grey result that likewise can be used to replace the L_eye value. This is used for the photograph of NGC6946.

Finally, these images are combined to a colour image in .BMP format and compressed to a Jpeg-format.