Robin, I am very pleased that you have been so attentive to my troubles. And for that I take the opportunity to learn more. I only point out that the PVs in my graph are extracted from the G-band of white surface images. With RAW I cannot operate, I have to learn how to do it. Now your graphic result unbalances me quite a bit. It is exactly what I would like to have with my nikon. For the last 5 years I have been observing the colours of sunrise and sunset by mathematically processing RGB images, but without the need to do photometry. Now, I intend to start systematic observations of the brightness of the sky at zenith in the 3 RG&B bands. This is why I need the numerical pixel values. Unfortunately, my problem is also English, which I know very little. Reading and understanding just a few pages of a manual is a real feat; if it is American English, I often have to give up. The translation into English of articles I write in Italian I always entrust to a professional translator, which is not easy to find here in Italy. My wife could help me, but you know how women are, especially wives lose patience immediately. Which is obviously not allowed to me, when there are jobs (especially difficult and heavy ones) to be done around the house: immediately and done right! Anyway, I will follow your instructions very carefully.
Sincerely regards
British Astronomical Association
Supporting amateur astronomers since 1890